Astronomers using observations from NASA's Kepler and Swift missions have discovered a batch of rapidly spinning stars that produce X-rays at more than 100 times the peak levels ever seen from the sun. The stars, which spin so fast they've been squashed into pumpkin-like shapes, are thought to be the result of close binary systems where two sun-like stars merge.

"These 18 stars rotate in just a few days on average, while the sun takes nearly a month," said Steve Howell, a senior research scientist at NASA's Ames Research Center in Moffett Field, California, and leader of the team. "The rapid rotation amplifies the same kind of activity we see on the sun, such as sunspots and solar flares, and essentially sends it into overdrive."

The most extreme member of the group, a K-type orange giant dubbed KSw 71, is more than 10 times larger than the sun, rotates in just 5.5 days, and produces X-ray emission 4,000 times greater than the sun does at solar maximum.

This artist's concept illustrates how the most extreme "pumpkin star" found by Kepler and Swift compares with the sun. Both stars are shown to scale. KSw 71 is larger, cooler and redder than the sun and rotates four times faster. Rapid spin causes the star to flatten into a pumpkin shape, which results in brighter poles and a darker equator. Rapid rotation also drives increased levels of stellar activity such as starspots, flares and prominences, producing X-ray emission over 4,000 times more intense than the peak emission from the sun. KSw 71 is thought to have recently formed following the merger of two sun-like stars in a close binary system.

Credits: NASA's Goddard Space Flight Center/Francis Reddy

These rare stars were found as part of an X-ray survey of the original Kepler field of view, a patch of the sky comprising parts of the constellations Cygnus and Lyra. From May 2009 to May 2013, Kepler measured the brightness of more than 150,000 stars in this region to detect the regular dimming from planets passing in front of their host stars. The mission was immensely successful, netting more than 2,300 confirmed exoplanets and nearly 5,000 candidates to date. An ongoing extended mission, called K2, continues this work in areas of the sky located along the ecliptic, the plane of Earth's orbit around the sun.

"A side benefit of the Kepler mission is that its initial field of view is now one of the best-studied parts of the sky," said team member Padi Boyd, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who designed the Swift survey. For example, the entire area was observed in infrared light by NASA's Wide-field Infrared Survey Explorer, and NASA's Galaxy Evolution Explorer observed many parts of it in the ultraviolet. "Our group was looking for variable X-ray sources with optical counterparts seen by Kepler, especially active galaxies, where a central black hole drives the emissions," she explained.

Using the X-ray and ultraviolet/optical telescopes aboard Swift, the researchers conducted the Kepler–Swift Active Galaxies and Stars Survey (KSwAGS), imaging about six square degrees, or 12 times the apparent size of a full moon, in the Kepler field.

"With KSwAGS we found 93 new X-ray sources, about evenly split between active galaxies and various types of X-ray stars," said team member Krista Lynne Smith, a graduate student at the University of Maryland, College Park who led the analysis of Swift data. "Many of these sources have never been observed before in X-rays or ultraviolet light."

For the brightest sources, the team obtained spectra using the 200-inch telescope at Palomar Observatory in California. These spectra provide detailed chemical portraits of the stars and show clear evidence of enhanced stellar activity, particularly strong diagnostic lines of calcium and hydrogen.

The researchers used Kepler measurements to determine the rotation periods and sizes for 10 of the stars, which range from 2.9 to 10.5 times larger than the sun. Their surface temperatures range from somewhat hotter to slightly cooler than the sun, mostly spanning spectral types F through K. Astronomers classify the stars as subgiants and giants, which are more advanced evolutionary phases than the sun's caused by greater depletion of their primary fuel source, hydrogen. All of them eventually will become much larger red giant stars.

A paper detailing the findings will be published in the Nov. 1 edition of the Astrophysical Journal and is now available online.

Forty years ago, Ronald Webbink at the University of Illinois, Urbana-Champaign noted that close binary systems cannot survive once the fuel supply of one star dwindles and it starts to enlarge. The stars coalesce to form a single rapidly spinning star initially residing in a so-called "excretion" disk formed by gas thrown out during the merger. The disk dissipates over the next 100 million years, leaving behind a very active, rapidly spinning star.

Howell and his colleagues suggest that their 18 KSwAGS stars formed by this scenario and have only recently dissipated their disks. To identify so many stars passing through such a cosmically brief phase of development is a real boon to stellar astronomers.

"Webbink's model suggests we should find about 160 of these stars in the entire Kepler field," said co-author Elena Mason, a researcher at the Italian National Institute for Astrophysics Astronomical Observatory of Trieste. "What we have found is in line with theoretical expectations when we account for the small portion of the field we observed with Swift."

The team has already extended their Swift observations to additional fields mapped by the K2 mission.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

Goddard manages the Swift mission in collaboration with Pennsylvania State University in University Park, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.

Related Links

• NASA's Kepler and K2 mission website
• NASA's Swift mission website

This artist's concept depicts "heartbeat stars," which have been detected by NASA's Kepler Space Telescope and others.

Credits: NASA/JPL-Caltech

Full image and caption

Matters of the heart can be puzzling and mysterious -- so too with unusual astronomical objects called heartbeat stars.

Heartbeat stars, discovered in large numbers by NASA's Kepler space telescope, are binary stars (systems of two stars orbiting each other) that got their name because if you were to map out their brightness over time, the result would look like an electrocardiogram, a graph of the electrical activity of the heart. Scientists are interested in them because they are binary systems in elongated elliptical orbits. This makes them natural laboratories for studying the gravitational effects of stars on each other.

In a heartbeat star system, the distance between the two stars varies drastically as they orbit each other. Heartbeat stars can get as close as a few stellar radii to each other, and as far as 10 times that distance during the course of one orbit.

At the point of their closest encounter, the stars’ mutual gravitational pull causes them to become slightly ellipsoidal in shape, which is one of the reasons their light is so variable. This is the same type of "tidal force" that causes ocean tides on Earth. By studying heartbeat stars, astronomers can gain a better understanding of how this phenomenon works for different kinds of stars.

Tidal forces also cause heartbeat stars to vibrate or "ring" -- in other words, the diameters of the stars rapidly fluctuate as they orbit each other. This effect is most noticeable at the point of closest approach.

“You can think about the stars as bells, and once every orbital revolution, when the stars reach their closest approach, it's as if they hit each other with a hammer,” said Avi Shporer, NASA Sagan postdoctoral fellow at NASA's Jet Propulsion Laboratory, Pasadena, California, and lead author of a recent study on heartbeat stars. "One or both stars vibrate throughout their orbits, and when they get nearer to each other, it's as though they are ringing very loudly."     

Kepler, now in its K2 Mission, discovered large numbers of heartbeat stars just in the last several years. A 2011 study discussed a star called KOI-54 that shows an increase in brightness every 41.8 days. In 2012, a subsequent study characterized 17 additional objects in the Kepler data and dubbed them "heartbeat stars." To characterize these unique systems, further data and research were required.

Shporer's study, published in the Astrophysical Journal, measured the orbits of 19 heartbeat star systems -- the largest batch ever characterized in a single study. The authors followed up on known heartbeat stars, previously identified by the Kepler mission. Specifically, they used an instrument on the W.M. Keck Observatory telescope in Hawaii called the High Resolution Echelle Spectrometer (HIRES), which measures the wavelengths of incoming light, which are stretched out when a star is moving away from us and shorter in motion toward us. This information allows astronomers to calculate the speed of the objects along the line of sight, and measure the shape of the orbit.

"We found that the heartbeat stars in our sample tend to be hotter than the sun and bigger than the sun," Shporer said. "But it is possible that there are others with different temperature ranges that we did not yet measure."

Study authors also postulate that some binary systems of heartbeat stars could have a third star in the system that has not yet been detected, or even a fourth star.

“The mere existence of heartbeat stars is a bit of a puzzle," said Susan Mullally (formerly Thompson), a SETI Institute scientist working for the Kepler Mission at NASA's Ames Research Center in Moffett Field, California, and co-author of the study. "All the tidal stretching of these heartbeat stars should have quickly caused the system to evolve into a circular orbit. A third star in the system is one way to create the highly stretched-out, elliptical orbits we observe."

Researchers are currently pursuing follow-up studies to search for third-star components in heartbeat star systems.

"We look forward to continued collaboration between ground and space observatories to better understand the complex inner workings of heartbeat stars," Shporer said.

NASA Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. JPL managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. Work on this study was performed in part under contract with JPL funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute.

For more information about the Kepler and K2 missions, visit:

http://www.nasa.gov/kepler

This illustration represents how hot Jupiters of different temperatures and different cloud compositions might appear to a person flying over the dayside of these planets on a spaceship, based on computer modeling.

Credits: NASA/JPL-Caltech/University of Arizona/V. Parmentier

Full image and caption

The weather forecast for faraway, blistering planets called "hot Jupiters" might go something like this: Cloudy nights and sunny days, with a high of 2,400 degrees Fahrenheit (about 1,300 degrees Celsius, or 1,600 Kelvin).

These mysterious worlds are too far away for us to see clouds in their atmospheres. But a recent study using NASA's Kepler space telescope and computer modeling techniques finds clues to where such clouds might gather and what they're likely made of. The study was published in the Astrophysical Journal and is also available on the arXiv.

Hot Jupiters, among the first of the thousands of exoplanets (planets outside our solar system) discovered in our galaxy so far, orbit their stars so tightly that they are perpetually charbroiled. And while that might discourage galactic vacationers, the study represents a significant advance in understanding the structure of alien atmospheres.

Endless days, endless nights

Hot Jupiters are tidally locked, meaning one side of the planet always faces its sun and the other is in permanent darkness. In most cases, the "dayside" would be largely cloud-free and the "nightside" heavily clouded, leaving partly cloudy skies for the zone in between, the study shows.

"The cloud formation is very different from what we know in the solar system," said Vivien Parmentier, a NASA Sagan Fellow and postdoctoral researcher at the University of Arizona, Tucson, who was the lead author of the study.

A "year" on such a planet can be only a few Earth days long, the time the planet takes to whip once around its star. On a "cooler" hot Jupiter, temperatures of, say, 2,400 degrees Fahrenheit might prevail.

But the extreme conditions on hot Jupiters worked to the scientists’ advantage.

"The day-night radiation contrast is, in fact, easy to model," Parmentier said. “[The hot Jupiters] are much easier to model than Jupiter itself."

An eclipse, then blips

The scientists first created a variety of idealized hot Jupiters using global circulation models -- simpler versions of the type of computer models used to simulate Earth’s climate.

Then they compared the models to the light Kepler detected from real hot Jupiters. Kepler, which is now operating in its K2 mission, was designed to register the extremely tiny dip in starlight when a planet passes in front of its star, which is called a "transit." But in this case, researchers focused on the planets' "phase curves," or changes in light as the planet passes through phases, like Earth’s moon.

Matching the modeled hot Jupiters to phase curves from real hot Jupiters revealed which curves were caused by the planet’s heat, and which by light reflected by clouds in its atmosphere. By combining Kepler data with computer models, scientists were able to infer global cloud patterns on these distant worlds for the first time.

The new cloud view allowed the team to draw conclusions about wind and temperature differences on the hot Jupiters they studied. Just before the hotter planets passed behind their stars -- in a kind of eclipse -- a blip in the planet’s optical light curve revealed a "hot spot" on the planet’s eastern side.

And on cooler eclipsing planets, a blip was seen just after the planet re-emerged on the other side of the star, this time on the planet’s western side.

The early blip on hotter worlds reveals that powerful winds were pushing the hottest, cloud-free part of the atmosphere, normally found directly beneath its sun, to the east. Meanwhile, on cooler worlds, clouds could bunch up and reflect more light on the "colder," western side of the planet, causing the post-eclipse blip.

"We’re claiming that the west side of the planet’s dayside is more cloudy than the east side," Parmentier said.

While the puzzling pattern has been seen before, this research was the first to study all the hot Jupiters showing this behavior.

This led to another first. By figuring out how clouds are distributed, which is intimately tied to the planet’s overall temperature, scientists were able to determine what the clouds were probably made of.

Just add manganese, and stir

Hot Jupiters are far too hot for water-vapor clouds like those on Earth. Instead, clouds on these planets are likely formed as exotic vapors condense to form minerals, chemical compounds like aluminum oxide, or even metals, like iron.

The science team found that manganese sulfide clouds probably dominate on "cooler" hot Jupiters, while silicate clouds prevail at higher temperatures. On these planets, the silicates likely "rain out" into the planet’s interior, vanishing from the observable atmosphere.

In other words, a planet’s average temperature, which depends on its distance from its star, governs the kinds of clouds that can form. That leads to different planets forming different types of clouds.

"Cloud composition changes with planet temperature," Parmentier said. "The offsetting light curves tell the tale of cloud composition. It’s super interesting, because cloud composition is very hard to get otherwise."

The new results also show that clouds are not evenly distributed on hot Jupiters, echoing previous findings from NASA’s Spitzer Space Telescope suggesting that different parts of hot Jupiters have vastly different temperatures.

The new findings come as we mark the 21st anniversary of exoplanet hunting. On Oct. 6, 1995, a Swiss team announced the discovery of 51 Pegasi b, a hot Jupiter that was the first planet to be confirmed in orbit around a sun-like star. Parmentier and his team hope their revelations about the clouds on hot Jupiters could bring more detailed understanding of hot Jupiter atmospheres and their chemistry, a major goal of exoplanet atmospheric studies.

NASA Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder. This work was performed in part under contract with JPL, funded by NASA through the Sagan Fellowship Program, executed by the NASA Exoplanet Science Institute.

For more information on the Kepler and the K2 mission, visit:

http://www.nasa.gov/kepler

For more information about exoplanets, visit:

https://exoplanets.nasa.gov/

Great balls of fire! NASA's Hubble Space Telescope has detected superhot blobs of gas, each twice as massive as the planet Mars, being ejected near a dying star. The plasma balls are zooming so fast through space it would take only 30 minutes for them to travel from Earth to the moon. This stellar "cannon fire" has continued once every 8.5 years for at least the past 400 years, astronomers estimate.

The fireballs present a puzzle to astronomers, because the ejected material could not have been shot out by the host star, called V Hydrae. The star is a bloated red giant, residing 1,200 light-years away, which has probably shed at least half of its mass into space during its death throes. Red giants are dying stars in the late stages of life that are exhausting their nuclear fuel that makes them shine. They have expanded in size and are shedding their outer layers into space.

This four-panel graphic illustrates how the binary-star system V Hydrae is launching balls of plasma into space. Panel 1 shows the two stars orbiting each other. One of the stars is nearing the end of its life and has swelled in size, becoming a red giant. In panel 2, the smaller star's orbit carries the star into the red giant's expanded atmosphere. As the star moves through the atmosphere, it gobbles up material from the red giant, which settles into a disk around the star. The buildup of material reaches a tipping point and is eventually ejected as blobs of hot plasma along the star's spin axis, shown in panel 3. This ejection process is repeated every eight years, the time it takes for the orbiting star to make another pass through the bloated red giant's envelope, shown in panel 4.

Credits: NASA, ESA, and A. Feild (STScI)

The current best explanation suggests the plasma balls were launched by an unseen companion star. According to this theory, the companion would have to be in an elliptical orbit that carries it close to the red giant's puffed-up atmosphere every 8.5 years. As the companion enters the bloated star's outer atmosphere, it gobbles up material. This material then settles into a disk around the companion, and serves as the launching pad for blobs of plasma, which travel at roughly a half-million miles per hour.

This star system could be the archetype to explain a dazzling variety of glowing shapes uncovered by Hubble that are seen around dying stars, called planetary nebulae, researchers say. A planetary nebula is an expanding shell of glowing gas expelled by a star late in its life.

"We knew this object had a high-speed outflow from previous data, but this is the first time we are seeing this process in action," said Raghvendra Sahai of NASA's Jet Propulsion Laboratory in Pasadena, California, lead author of the study. "We suggest that these gaseous blobs produced during this late phase of a star's life help make the structures seen in planetary nebulae."

Hubble observations over the past two decades have revealed an enormous complexity and diversity of structure in planetary nebulae. The telescope's high resolution captured knots of material in the glowing gas clouds surrounding the dying stars. Astronomers speculated that these knots were actually jets ejected by disks of material around companion stars that were not visible in the Hubble images. Most stars in our Milky Way galaxy are members of binary systems. But the details of how these jets were produced remained a mystery.

"We want to identify the process that causes these amazing transformations from a puffed-up red giant to a beautiful, glowing planetary nebula," Sahai said. "These dramatic changes occur over roughly 200 to 1,000 years, which is the blink of an eye in cosmic time."

Sahai's team used Hubble's Space Telescope Imaging Spectrograph (STIS) to conduct observations of V Hydrae and its surrounding region over an 11-year period, first from 2002 to 2004, and then from 2011 to 2013. Spectroscopy decodes light from an object, revealing information on its velocity, temperature, location, and motion.

The data showed a string of monstrous, super-hot blobs, each with a temperature of more than 17,000 degrees Fahrenheit - almost twice as hot as the surface of the sun.

The researchers compiled a detailed map of the blobs' location, allowing them to trace the first behemoth clumps back to 1986. "The observations show the blobs moving over time," Sahai said. "The STIS data show blobs that have just been ejected, blobs that have moved a little farther away, and blobs that are even farther away." STIS detected the giant structures as far away as 37 billion miles away from V Hydrae, more than eight times farther away than the Kuiper Belt of icy debris at the edge of our solar system is from the sun.

The blobs expand and cool as they move farther away, and are then not detectable in visible light. But observations taken at longer sub-millimeter wavelengths in 2004, by the Submillimeter Array in Hawaii, revealed fuzzy, knotty structures that may be blobs launched 400 years ago, the researchers said.

Based on the observations, Sahai and his colleagues Mark Morris of the University of California, Los Angeles, and Samantha Scibelli of the State University of New York at Stony Brook developed a model of a companion star with an accretion disk to explain the ejection process.

"This model provides the most plausible explanation because we know that the engines that produce jets are accretion disks," Sahai explained. "Red giants don't have accretion disks, but many most likely have companion stars, which presumably have lower masses because they are evolving more slowly. The model we propose can help explain the presence of bipolar planetary nebulae, the presence of knotty jet-like structures in many of these objects, and even multipolar planetary nebulae. We think this model has very wide applicability."

A surprise from the STIS observation was that the disk does not fire the monster clumps in exactly the same direction every 8.5 years. The direction flip-flops slightly from side-to-side to back-and-forth due to a possible wobble in the accretion disk. "This discovery was quite surprising, but it is very pleasing as well because it helped explain some other mysterious things that had been observed about this star by others," Sahai said.

Astronomers have noted that V Hydrae is obscured every 17 years, as if something is blocking its light. Sahai and his colleagues suggest that due to the back-and-forth wobble of the jet direction, the blobs alternate between passing behind and in front of V Hydrae. When a blob passes in front of V Hydrae, it shields the red giant from view.

"This accretion disk engine is very stable because it has been able to launch these structures for hundreds of years without falling apart," Sahai said. "In many of these systems, the gravitational attraction can cause the companion to actually spiral into the core of the red giant star. Eventually, though, the orbit of V Hydrae's companion will continue to decay because it is losing energy in this frictional interaction. However, we do not know the ultimate fate of this companion."

The team hopes to use Hubble to conduct further observations of the V Hydrae system, including the most recent blob ejected in 2011. The astronomers also plan to use the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study blobs launched over the past few hundred years that are now too cool to be detected with Hubble.

The team's results appeared in the August 20, 2016, issue of The Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt,

Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

For images and more information about V Hydrae and Hubble, visit:

http://hubblesite.org/news/2016/34

www.nasa.gov/hubble

Artist concept of Transiting Exoplanet Survey Satellite.

Credits: NASA's Goddard Space Flight Center/Chris Meaney

NASA's search for planets outside of our solar system has mostly involved very distant, faint stars. NASA’s upcoming Transiting Exoplanet Survey Satellite (TESS), by contrast, will look at the brightest stars in our solar neighborhood.

After TESS launches, it will quickly start discovering new exoplanets that ground-based observatories, the Hubble Space Telescope and, later, the James Webb Space Telescope, will target for follow-up studies. TESS is scheduled to launch no later than June 2018. Astronomers are eagerly anticipating the possibility that, in the near future, all three space missions could be studying the sky at the same time.

“The problem is that we’ve had very few exoplanet targets that are good for follow-up,” said TESS Project Scientist Stephen Rinehart at NASA's Goddard Space Flight Center in Greenbelt, Maryland. “TESS will change that.”

Planets around closer, brighter stars are ideal for follow-up study because they'll produce stronger signals than planets around more distant stars. These planets have a higher signal-to-noise ratio, which measures the ratio of useful information — the signal — to non-useful information — the noise — that a telescope receives. These signals might also include a chemical sampling of an exoplanet's atmosphere, which is an exciting prospect for scientists hoping to search for signs of life on distant worlds.

TESS will do the initial roundup of exoplanets, with the potential to identify thousands during its projected two-year mission. One of TESS’ main science goals is to identify 50 rocky worlds, like Earth or Venus, whose masses can be measured.

“The search for exoplanets is a bit like a funnel where you pour in lots of stars,” said TESS Deputy Science Director Sara Seager at the Massachusetts Institute of Technology (MIT), Cambridge. “At the end of the day, you have loads of planets, and from there you need to find the rocky ones.”

The TESS Science Center will help identify and prioritize the TESS Objects of Interest (TOI) for follow-up. TOI are objects that scientists believe could be exoplanets based on TESS data. Ground-based telescopes will confirm which TOI are exoplanets, and from there will help determine which are rocky. The center is a partnership between MIT's Physics Department and Kavli Institute for Astrophysics and Space Research — where TESS Principle Investigator George Ricker resides — the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, and NASA’s Ames Research Center in Moffett Field, California.

The main thing space- and ground-based telescopes hope to find out about the TESS targets with follow-up observations is what these exoplanet atmospheres are like. Exoplanet atmosphere exploration is one of the Webb telescope's four main science goals.

NASA's Webb telescope and ground-based telescopes will determine the atmospheres of exoplanets using spectroscopy. In this process, telescopes look at the chemical signatures of the light passing through exoplanet atmospheres. This signature can tells scientists what chemicals are in the planetary atmosphere, and how much of each there are. It can also help scientists determine whether a planet could be habitable.

“There are a couple of things we like to see as a potential for habitability – one of them is water, which is probably the single most important, because as far as we know, all life that we’re familiar with depends on water in some way,” Rinehart said. “The other is methane, which on our Earth is produced almost entirely biologically. When you start seeing certain combinations of all of these things appearing together – water, methane, ozone, oxygen – it gives you a hint that the chemistry is out of equilibrium. Naturally, planets tend to be chemically stable. The presence of life throws off this balance.”

Exoplanets aren’t the only science that will come out of the TESS all-sky survey, however. While scientists expect to spot a transit signal that could reveal exoplanets around only about one out of 100 stars, virtually every star in the sky will be monitored carefully and continuously for at least 27 days, resulting in a wide variety of variability to be explored.

The TESS Guest Investigator (GI) Program will allow for deeper investigations of astronomically interesting objects, either through TESS data alone, or by identifying interesting variables for further study with the Webb telescope, Hubble and other ground- and space-based telescopes. The GI Program will look at variable objects, such as flare stars, active galaxies and supernovae, and may even discover optical counterparts to distant transient events, such as gamma-ray bursts. Only the number and type of exciting proposed ideas the program receives limit what TESS will find through the GI Program. 

Between the mission’s exoplanet survey and the GI Program, TESS will provide the best follow-up targets for many missions to come.

“TESS not only will provide targets for the Webb telescope, but for every telescope we plan to build on the ground and in space over the next two decades,” said Mark Clampin, director of the Astrophysics Science Division at Goddard. With such an exciting future, scientists from around the world are watching the progress of the TESS mission, and anxiously awaiting its launch.

Related Links

• NASA's TESS website
• TESS project website

Using data from NASA's Fermi Gamma-ray Space Telescope and other facilities, an international team of scientists has found the first gamma-ray binary in another galaxy and the most luminous one ever seen. The dual-star system, dubbed LMC P3, contains a massive star and a crushed stellar core that interact to produce a cyclic flood of gamma rays, the highest-energy form of light.

"Fermi has detected only five of these systems in our own galaxy, so finding one so luminous and distant is quite exciting," said lead researcher Robin Corbet at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Gamma-ray binaries are prized because the gamma-ray output changes significantly during each orbit and sometimes over longer time scales. This variation lets us study many of the emission processes common to other gamma-ray sources in unique detail."

These rare systems contain either a neutron star or a black hole and radiate most of their energy in the form of gamma rays. Remarkably, LMC P3 is the most luminous such system known in gamma rays, X-rays, radio waves and visible light, and it's only the second one discovered with Fermi.

A paper describing the discovery will appear in the Oct. 1 issue of The Astrophysical Journal and is now available online.

LMC P3 lies within the expanding debris of a supernova explosion located in the Large Magellanic Cloud (LMC), a small nearby galaxy about 163,000 light-years away. In 2012, scientists using NASA's Chandra X-ray Observatory found a strong X-ray source within the supernova remnant and showed that it was orbiting a hot, young star many times the sun's mass. The researchers concluded the compact object was either a neutron star or a black hole and classified the system as a high-mass X-ray binary (HMXB).

In 2015, Corbet's team began looking for new gamma-ray binaries in Fermi data by searching for the periodic changes characteristic of these systems. The scientists discovered a 10.3-day cyclic change centered near one of several gamma-ray point sources recently identified in the LMC. One of them, called P3, was not linked to objects seen at any other wavelengths but was located near the HMXB. Were they the same object?

Observations from Fermi's Large Area Telescope (magenta line) show that gamma rays from LMC P3 rise and fall over the course of 10.3 days. The companion is thought to be a neutron star. Illustrations across the top show how the changing position of the neutron star relates to the gamma-ray cycle.

Credits: NASA's Goddard Space Flight Center

To find out, Corbet's team observed the binary in X-rays using NASA's Swift satellite, at radio wavelengths with the Australia Telescope Compact Array near Narrabri and in visible light using the 4.1-meter Southern Astrophysical Research Telescope on Cerro Pachón in Chile and the 1.9-meter telescope at the South African Astronomical Observatory near Cape Town.

The Swift observations clearly reveal the same 10.3-day emission cycle seen in gamma rays by Fermi. They also indicate that the brightest X-ray emission occurs opposite the gamma-ray peak, so when one reaches maximum the other is at minimum. Radio data exhibit the same period and out-of-phase relationship with the gamma-ray peak, confirming that LMC P3 is indeed the same system investigated by Chandra.

"The optical observations show changes due to binary orbital motion, but because we don't know how the orbit is tilted into our line of sight, we can only estimate the individual masses," said team member Jay Strader, an astrophysicist at Michigan State University in East Lansing. "The star is between 25 and 40 times the sun's mass, and if we're viewing the system at an angle midway between face-on and edge-on, which seems most likely, its companion is a neutron star about twice the sun's mass." If, however, we view the binary nearly face-on, then the companion must be significantly more massive and a black hole.

LMC P3 (circled) is located in a supernova remnant called DEM L241 in the Large Magellanic Cloud, a small galaxy about 163,000 light-years away. The system is the first gamma-ray binary discovered in another galaxy and is the most luminous known in gamma rays, X-rays, radio waves and visible light.

Unlabeled image

Both objects form when a massive star runs out of fuel, collapses under its own weight and explodes as a supernova. The star's crushed core may become a neutron star, with the mass of half a million Earths squeezed into a ball no larger than Washington, D.C. Or it may be further compacted into a black hole, with a gravitational field so strong not even light can escape it.

The surface of the star at the heart of LMC P3 has a temperature exceeding 60,000 degrees Fahrenheit (33,000 degrees Celsius), or more than six times hotter than the sun's. The star is so luminous that pressure from the light it emits actually drives material from the surface, creating particle outflows with speeds of several million miles an hour.

In gamma-ray binaries, the compact companion is thought to produce a "wind" of its own, one consisting of electrons accelerated to near the speed of light. The interacting outflows produce X-rays and radio waves throughout the orbit, but these emissions are detected most strongly when the compact companion travels along the part of its orbit closest to Earth.  

Through a different mechanism, the electron wind also emits gamma rays. When light from the star collides with high-energy electrons, it receives a boost to gamma-ray levels. Called inverse Compton scattering, this process produces more gamma rays when the compact companion passes near the star on the far side of its orbit as seen from our perspective.

Prior to Fermi's launch, gamma-ray binaries were expected to be more numerous than they've turned out to be. Hundreds of HMXBs are cataloged, and these systems are thought to have originated as gamma-ray binaries following the supernova that formed the compact object.

"It is certainly a surprise to detect a gamma-ray binary in another galaxy before we find more of them in our own," said Guillaume Dubus, a team member at the Institute of Planetology and Astrophysics of Grenoble in France. "One possibility is that the gamma-ray binaries Fermi has found are rare cases where a supernova formed a neutron star with exceptionally rapid spin, which would enhance how it produces accelerated particles and gamma rays."

NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

Two's company, but three might not always be a crowd — at least in space.

Astronomers using NASA's Hubble Space Telescope, and a trick of nature, have confirmed the existence of a planet orbiting two stars in the system OGLE-2007-BLG-349, located 8,000 light-years away towards the center of our galaxy.

The planet orbits roughly 300 million miles from the stellar duo, about the distance from the asteroid belt to our sun. It completes an orbit around both stars roughly every seven years. The two red dwarf stars are a mere 7 million miles apart, or 14 times the diameter of the moon's orbit around Earth.

This artist's illustration shows a gas giant planet circling a pair of red dwarf stars in the system OGLE-2007-BLG-349, located 8,000 light-years away. The Saturn-mass planet orbits roughly 300 million miles from the stellar duo. The two red dwarf stars are 7 million miles apart.

Credits: NASA, ESA, and G. Bacon (STScI)

The Hubble observations represent the first time such a three-body system has been confirmed using the gravitational microlensing technique. Gravitational microlensing occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.

The three objects were discovered in 2007 by an international collaboration of five different groups: Microlensing Observations in Astrophysics (MOA), the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing Lensing Anomalies Network (PLANET), and the Robonet Collaboration. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify.

"The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star," explained David Bennett of the NASA Goddard Space Flight Center in Greenbelt, Maryland, the paper's first author.

The sharpness of the Hubble images allowed the research team to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun. "So, the model with two stars and one planet is the only one consistent with the Hubble data," Bennett said.

Bennett's team conducted the follow-up observations with Hubble's Wide Field Planetary Camera 2. "We were helped in the analysis by the almost perfect alignment of the foreground binary stars with the background star, which greatly magnified the light and allowed us to see the signal of the two stars," Bennett explained.

Kepler has discovered 10 other planets orbiting tight binary stars, but these are all much closer to their stars than the one studied by Hubble.

Now that the team has shown that microlensing can successfully detect planets orbiting double-star systems, Hubble could provide an essential role in this new realm in the continued search for exoplanets.

The team's results have been accepted for publication in The Astronomical Journal.

When it comes to exoplanets, astronomers have realized that they only know the properties of the planets they discover as well as they know the properties of the stars being orbited. For a planet's size, precisely characterizing the host star can mean the difference in our understanding of whether a distant world is small like Earth or huge like Jupiter.

For astronomers to determine the size of an exoplanet—planets outside the solar system—depends critically on knowing not only the radius of its host star but also whether that star is single or has a close companion. Consider that about half of the stars in the sky are not one but two stars orbiting around each other, this makes knowing the binary property of a star paramount.

One particularly interesting and relatively nearby star, named TRAPPIST-1, recently caught the attention of a team of researchers. They wanted to determine if TRAPPIST-1, which is home to three small, potentially rocky planets—one of which orbits in the temperate habitable zone where liquid water might pool on the surface—was a single star like the sun, or if it had a companion star. If TRAPPIST-1 did have a companion star, the discovered planets will have larger sizes, possibly large enough to be ice giants similar to Neptune.

If an exoplanet orbits a star in a binary system but astronomers believe the starlight captured by the telescope is from a single star, the real radius of the planet will be larger than measured. The difference in the measured size of the exoplanet can be small ranging from 10 percent to more than a factor of two in size, depending on the brightness of the companion star in the system.

To confirm or deny the single star nature of TRAPPIST-1, Steve Howell, senior research scientist at NASA's Ames Research Center at Moffett Field, California, led an investigation of the star. Using a specially designed camera, called the Differential Speckle Survey Instrument or DSSI, Howell and his team measured the rapid disturbances in the light emitted by the star caused by the Earth’s atmosphere and corrected for them. The resultant high-resolution image revealed that the light coming from the TRAPPIST-1 system is from a single star.

With the confirmation that no other companion star resides in the vicinity of TRAPPIST-1, the research team's result validates not only that transiting planets are responsible for the periodic dips seen in the star’s brightness but that they are indeed Earth-size and may likely to be rocky worlds.

"Knowing that a terrestrial-size potentially rocky planet orbits in the habitable zone of a star only 40 light-years from the Earth is an awesome finding," said Howell. “The TRAPPIST-1 system will continue to be studied in great detail as these transiting exoplanets offer one of the best chances to characterize the atmosphere of an alien world."

Mounted on the 8-meter Gemini Observatory South telescope in Chile, the DSSI provided astronomers with the highest resolution images available today from a single ground-based telescope. The nearness of TRAPPIST-1 allowed astronomers to peer deep into the system, looking closer than Mercury's orbit to our sun.

The paper the result is based on is published in the September 13th issue of The Astrophysical Journal Letters.

Interest in the recently-discovered TRAPPIST-1 with its three Earth-size planets is high. Astronomically speaking, at 40 light-years from Earth, the system is a hop, skip and a jump away. The star itself is a dim M-type star, which, relative to most stars, is very small and cool, but making transit detection of small planets easier.

Further detailed measurement of the planetary transits seen in TRAPPIST-1 will begin later this year when NASA's Kepler space telescope in its K2 mission will precisely monitor minute changes in the light emitted from the star for a period of about 75 days.

The space-based observations from the Kepler spacecraft will provide extremely precise measurements of the planet transit shapes allowing for more refined radius and orbital period determination. Noting variations in the mid-time of the transit events can also help astronomers determine the planet masses. Additionally, the new observations will be searched for more transiting planets in the TRAPPIST-1 system.

Speckle interferometry, the imaging technique used by the DSSI, is a powerful asset in the astronomer's toolkit as it provides a unique capability to characterize the environment around distant stars. The technique provides ultra high-resolution images by taking multiple extremely short (40-60 millisecond) exposures of a star to capture fine detail in the received light and “freeze” the turbulence caused by Earth’s atmosphere.

By combining the many thousands of exposures and using mathematical techniques to remove the momentary distortions caused by Earth’s atmosphere, the final result provides a resolution equal to the theoretical limit of what the 8-meter Gemini telescope would produce if no atmosphere were present.

The four-panel graphic illustrates the difference of measured starlight when seen through a ground-based telescope with (top left corner) and without the blurring effects caused by Earth's atmosphere. The technique to neutralize Earth's atmospheric blur is called speckle interferometry. All four images are shown at the same scale.

Credits: Gemini Observatory/AURA and NASA/Ames/W. Stenzel

Howell and his team at NASA Ames are currently undertaking the construction of two new speckle interferometric instruments. One of the new instruments will be delivered this fall to the 3.5-meter WIYN telescope located at Kitt Peak National Observatory outside of Tucson, Arizona, where it will be used by the NN_EXPLORE guest observer research program. The other is being developed for the Gemini Observatory North telescope located on Mauna Kea in Hawaii.

NASA Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.

To learn more about the result from the Gemini Observatory, visit: http://www.gemini.edu/node/12567.

For more information on the Kepler and the K2 mission, visit: http://www.nasa.gov/kepler. 

An age-defying star designated as IRAS 19312+1950 (arrow) exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA’s Spitzer Space Telescope. A NASA-led team of scientists thinks the star – which is about 10 times as massive as our sun and emits about 20,000 times as much energy – is a newly forming protostar. That was a big surprise because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea.

Credits: NASA/JPL-Caltech

For an unannotated version of this image, click here.

For years, astronomers have puzzled over a massive star lodged deep in the Milky Way that shows conflicting signs of being extremely old and extremely young.

Researchers initially classified the star as elderly, perhaps a red supergiant. But a new study by a NASA-led team of researchers suggests that the object, labeled IRAS 19312+1950, might be something quite different – a protostar, a star still in the making.

“Astronomers recognized this object as noteworthy around the year 2000 and have been trying ever since to decide how far along its development is,” said Martin Cordiner, an astrochemist working at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He is the lead author of a paper in the Astrophysical Journal describing the team’s findings, from observations made using NASA’s Spitzer Space Telescope and ESA’s Herschel Space Observatory.

Located more than 12,000 light-years from Earth, the object first stood out as peculiar when it was observed at particular radio frequencies. Several teams of astronomers studied it using ground-based telescopes and concluded that it is an oxygen-rich star about 10 times as massive as the sun. The question was: What kind of star?

Some researchers favor the idea that the star is evolved – past the peak of its life cycle and on the decline. For most of their lives, stars obtain their energy by fusing hydrogen in their cores, as the sun does now. But older stars have used up most of their hydrogen and must rely on heavier fuels that don't last as long, leading to rapid deterioration.

Two early clues – intense radio sources called masers – suggested the star was old. In astronomy, masers occur when the molecules in certain kinds of gases get revved up and emit a lot of radiation over a very limited range of frequencies. The result is a powerful radio beacon – the microwave equivalent of a laser.

One maser observed with IRAS 19312+1950 is almost exclusively associated with late-stage stars. This is the silicon oxide maser, produced by molecules made of one silicon atom and one oxygen atom. Researchers don’t know why this maser is nearly always restricted to elderly stars, but of thousands of known silicon oxide masers, only a few exceptions to this rule have been noted.

Also spotted with the star was a hydroxyl maser, produced by molecules comprised of one oxygen atom and one hydrogen atom. Hydroxyl masers can occur in various kinds of astronomical objects, but when one occurs with an elderly star, the radio signal has a distinctive pattern – it’s especially strong at a frequency of 1612 megahertz. That’s the pattern researchers found in this case.

Even so, the object didn’t entirely fit with evolved stars. Especially puzzling was the smorgasbord of chemicals found in the large cloud of material surrounding the star. A chemical-rich cloud like this is typical of the regions where new stars are born, but no such stellar nursery had been identified near this star.

Scientists initially proposed that the object was an old star surrounded by a surprising cloud typical of the kind that usually accompanies young stars. Another idea was that the observations might somehow be capturing two objects: a very old star and an embryonic cloud of star-making material in the same field.

Cordiner and his colleagues began to reconsider the object, conducting observations using ESA’s Herschel Space Observatory and analyzing data gathered earlier with NASA’s Spitzer Space Telescope. Both telescopes operate at infrared wavelengths, which gave the team new insight into the gases, dust and ices in the cloud surrounding the star.

The additional information leads Cordiner and colleagues to think the star is in a very early stage of formation. The object is much brighter than it first appeared, they say, emitting about 20,000 times the energy of our sun. The team found large quantities of ices made from water and carbon dioxide in the cloud around the object. These ices are located on dust grains relatively close to the star, and all this dust and ice blocks out starlight making the star seem dimmer than it really is.

In addition, the dense cloud around the object appears to be collapsing, which happens when a growing star pulls in material. In contrast, the material around an evolved star is expanding and is in the process of escaping to the interstellar medium. The entire envelope of material has an estimated mass of 500 to 700 suns, which is much more than could have been produced by an elderly or dying star.

“We think the star is probably in an embryonic stage, getting near the end of its accretion stage – the period when it pulls in new material to fuel its growth,” said Cordiner.

Also supporting the idea of a young star are the very fast wind speeds measured in two jets of gas streaming away from opposite poles of the star. Such jets of material, known as a bipolar outflow, can be seen emanating from young or old stars. However, fast, narrowly focused jets are rarely observed in evolved stars. In this case, the team measured winds at the breakneck speed of at least 200,000 miles per hour (90 kilometers per second) – a common characteristic of a protostar.

Still, the researchers acknowledge that the object is not a typical protostar. For reasons they can’t explain yet, the star has spectacular features of both a very young and a very old star.

“No matter how one looks at this object, it’s fascinating, and it has something new to tell us about the life cycles of stars,” said Steven Charnley, a Goddard astrochemist and co-author of the paper.

NASA's Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission, whose science operations are conducted at the Spitzer Science Center. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado.

Herschel is an ESA space observatory with science instruments provided by European-led principal investigator consortia and with important participation from NASA.

For more information, visit:

• www.nasa.gov/spitzer

Or contact:

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov

This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system. The double star Alpha Centauri AB also appears in the image. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface.

Credits: ESO/M. Kornmesser

A newly discovered, roughly Earth-sized planet orbiting our nearest neighboring star might be habitable, according to a team of astronomers using the European Southern Observatory's 3.6-meter telescope at La Silla, Chile, along with other telescopes around the world.

The exoplanet is at a distance from its star that allows temperatures mild enough for liquid water to pool on its surface.

"NASA congratulates ESO on the discovery of this intriguing planet that has captured the hopes and the imagination of the world," says Paul Hertz, Astrophysics Division Director at NASA Headquarters, Washington. "We look forward to learning more about the planet, whether it holds ingredients that could make it suitable for life." 

The new planet circles Proxima Centauri, the smallest member of a triple star system known to science fiction fans everywhere as Alpha Centauri. Just over 4 light-years away, Proxima is the closest star to Earth, besides our own sun. 

"This is really a game-changer in our field," said Olivier Guyon, a planet-hunting affiliate at NASA's Jet Propulsion Laboratory, Pasadena, California, and associate professor at the University of Arizona, Tucson. "The closest star to us has a possible rocky planet in the habitable zone. That's a huge deal. It also boosts the already existing, mounting body of evidence that such planets are near, and that several of them are probably sitting quite close to us. This is extremely exciting."

The science team that made the discovery, led by Guillem Anglada-Escudé of Queen Mary University of London, will publish its findings Aug. 25 in the journal Nature. The team traced subtle wobbles in the star revealing, the presence of a star-tugging planet.

They determined that the new planet, dubbed Proxima b, is at least 1.3 times the mass of Earth. It orbits its star far more closely than Mercury orbits our sun, taking only 11 days to complete a single orbit -- a "year" on Proxima b.

Long list of unknowns

The stunning announcement comes with plenty of caveats. While the new planet lies within its star's "habitable zone" -- a distance at which temperatures are right for liquid water -- scientists do not yet know if the planet has an atmosphere.

It also orbits a red-dwarf star, far smaller and cooler than our sun. The planet likely presents only one face to its star, as the moon does to Earth, instead of rotating through our familiar days and nights. And Proxima b could be subject to potentially life-extinguishing stellar flares.

"That's the worry in terms of habitability," said Scott Gaudi, an astronomy professor at Ohio State University, Columbus, and JPL affiliate credited with numerous exoplanet discoveries. "This thing is being bombarded by a fair amount of high-energy radiation. It's not obvious if it's going to have a magnetic field strong enough to prevent its whole atmosphere from getting blown away. But those are really hard calculations, and I certainly wouldn't put my money either way on that."

Despite the unknowns, the discovery was hailed by NASA exoplanet hunters as a major milestone on the road to finding other possible life-bearing worlds within our stellar neighborhood.

"It definitely gives us something to be excited about," said Sara Seager, a planetary science and physics professor at the Massachusetts Institute of Technology, Cambridge, and an exoplanet-hunting pioneer. "I think it will definitely motivate people to get moving."

'Not completely unexpected'

Statistical surveys of exoplanets -- planets orbiting other stars -- by NASA's Kepler space telescope have revealed a large proportion of small planets around small stars, she said.

The Kepler data suggest we should expect at least one potentially habitable, Earth-size planet orbiting M-type stars, like Proxima, within 10 light-years of our solar system.

So the latest discovery was "not completely unexpected. We're more lucky than surprised," Seager said. But it "helps buoy our confidence that planets are everywhere."

It's especially encouraging for upcoming space telescopes, which can contribute to the study of the new planet. The James Webb Space Telescope, launching in 2018, may be able to follow-up on this planet with spectroscopy to determine the contents of its atmosphere. NASA's Transiting Exoplanet Survey Satellite (TESS) will find similar planets in the habitable zone in the stellar backyard of our solar system in 2018.

One of TESS's goals is to find planets orbiting nearby M-dwarf stars like Proxima Centauri.

"It's great news just to know that M-dwarf planets could be as common as we think they are," Seager said.

Another possible inspiration Proxima b could reignite: the admittedly far-off goal of sending a probe to another solar system.

Bill Borucki, an exoplanet pioneer, said the new discovery might inspire more interstellar research, especially if Proxima b proves to have an atmosphere.

Coming generations of space and ground-based telescopes, including large ground telescopes now under construction, could yield more information about the planet, perhaps inspiring ideas on how to pay it a visit.

"It may be that the first time we get really good information is from the newer telescopes that may be coming online in a decade or two," said Borucki, now retired, the former principal investigator for Kepler, which has discovered the bulk of the more than 3,300 exoplanets found so far.

"Maybe people will talk about sending a probe to that star system," Borucki said. "I think it does provide some inspiration for an interstellar mission, because now we know there is a planet in the habitable zone, probably around the mass of Earth, around the closest star. I think it does inspire a future effort to go there and check it out."

To read the ESO press release, visit:

www.eso.org/public/news/eso1629/?lang

To learn more about NASA's Exoplanet Program, visit:

http://exoplanets.nasa.gov

This image shows the Pleiades cluster of stars as seen through the eyes of WISE, or NASA's Wide-field Infrared Survey Explorer.

Credits: NASA/JPL-Caltech/UCLA

Full image and caption

Like cosmic ballet dancers, the stars of the Pleiades cluster are spinning. But these celestial dancers are all twirling at different speeds. Astronomers have long wondered what determines the rotation rates of these stars.

By watching these stellar dancers, NASA's Kepler space telescope during its K2 mission has helped amass the most complete catalog of rotation periods for stars in a cluster. This information can help astronomers gain insight into where and how planets form around these stars, and how such stars evolve.    

"We hope that by comparing our results to other star clusters, we will learn more about the relationship between a star’s mass, its age, and even the history of its solar system," said Luisa Rebull, a research scientist at the Infrared Processing and Analysis Center at Caltech in Pasadena, California. She is the lead author of two new papers and a co-author on a third paper about these findings, all being published in the Astronomical Journal.

The Pleiades star cluster is one of the closest and most easily seen star clusters, residing just 445 light-years away from Earth, on average. At about 125 million years old, these stars -- known individually as Pleiads -- have reached stellar "young adulthood." In this stage of their lives, the stars are likely spinning the fastest they ever will.

As a typical star moves further along into adulthood, it loses some zip due to the copious emission of charged particles known as a stellar wind (in our solar system, we call this the solar wind). The charged particles are carried along the star’s magnetic fields, which overall exerts a braking effect on the rotation rate of the star.

Rebull and colleagues sought to delve deeper into these dynamics of stellar spin with Kepler. Given its field of view on the sky, Kepler observed approximately 1,000 stellar members of the Pleiades over the course of 72 days. The telescope measured the rotation rates of more than 750 stars in the Pleiades, including about 500 of the lowest-mass, tiniest, and dimmest cluster members, whose rotations could not previously be detected from ground-based instruments.

Kepler measurements of starlight infer the spin rate of a star by picking up small changes in its brightness. These changes result from "starspots" which, like the more-familiar sunspots on our sun, form when magnetic field concentrations prevent the normal release of energy at a star’s surface. The affected regions become cooler than their surroundings and appear dark in comparison.

As stars rotate, their starspots come in and out of Kepler’s view, offering a way to determine spin rate. Unlike the tiny, sunspot blemishes on our middle-aged sun, starspots can be gargantuan in stars as young as those in the Pleiades because stellar youth is associated with greater turbulence and magnetic activity. These starspots trigger larger brightness decreases, and make spin rate measurements easier to obtain.

During its observations of the Pleiades, a clear pattern emerged in the data: More massive stars tended to rotate slowly, while less massive stars tended to rotate rapidly. The big-and-slow stars' periods ranged from one to as many as 11 Earth-days. Many low-mass stars, however, took less than a day to complete a pirouette. (For comparison, our sedate sun revolves fully just once every 26 days.) The population of slow-rotating stars includes some ranging from a bit larger, hotter and more massive than our sun, down to other stars that are somewhat smaller, cooler and less massive. On the far end, the fast-rotating, fleet-footed, lowest-mass stars possess as little as a tenth of our sun’s mass. 

"In the 'ballet' of the Pleiades, we see that slow rotators tend to be more massive, whereas the fastest rotators tend to be very light stars," said Rebull.  

The main source of these differing spin rates is the internal structure of the stars, Rebull and colleagues suggest. Larger stars have a huge core enveloped in a thin layer of stellar material undergoing a process called convection, familiar to us from the circular motion of boiling water. Small stars, on the other hand, consist almost entirely of convective, roiling regions. As stars mature, the braking mechanism from magnetic fields more easily slows the spin rate of the thin, outermost layer of big stars than the comparatively thick, turbulent bulk of small stars.

Thanks to the Pleiades’ proximity, researchers think it should be possible to untangle the complex relationships between stars’ spin rates and other stellar properties. Those stellar properties, in turn, can influence the climates and habitability of a star’s hosted exoplanets. For instance, as spinning slows, so too does starspot generation, and the solar storms associated with starspots. Fewer solar storms means less intense, harmful radiation blasting into space and irradiating nearby planets and their potentially emerging biospheres.    

"The Pleiades star cluster provides an anchor for theoretical models of stellar rotation going both directions, younger and older," said Rebull. "We still have a lot we want to learn about how, when and why stars slow their spin rates and hang up their 'dance shoes,' so to speak."

Rebull and colleagues are now analyzing K2 mission data from an older star cluster, Praesepe, popularly known as the Beehive Cluster, to further explore this phenomenon in stellar structure and evolution.

"We’re really excited that K2 data of star clusters, such as the Pleiades, have provided astronomers with a bounty of new information and helped advance our knowledge of how stars rotate throughout their lives," said Steve Howell, project scientist for the K2 mission at NASA’s Ames Research Center in Moffett Field, California.

The K2 mission’s approach to studying stars employs the Kepler spacecraft's ability to precisely observe miniscule changes in starlight. Kepler’s primary mission ended in 2013, but more exoplanet and astrophysics observations continue with the K2 mission, which began in 2014.

Ames manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.

Using public data collected by NASA's Kepler mission, astronomers have catalogued the planet candidates that may be similar to our third rock from the sun. The tabulation of candidates will help astronomers focus their research efforts in the search for life.

The analysis, led by Stephen Kane, an associate professor of physics and astronomy at San Francisco State University in California, highlights 20 candidates in the Kepler trove that are less than twice the size of Earth and orbit their star in the conservative habitable zone—the range of distances where liquid water could pool on the surface of an orbiting planet. Of these 20 candidates, nine have been previously investigated and determined to be verified planets, including notables like Kepler-62f, Kepler-186f, Kepler-283c, Kepler-296f and Kepler-442b.

The results are presented in a paper accepted by the Astrophysical Journal. For a listing of the candidates and their properties, the paper can be reviewed at: http://arxiv.org/abs/1608.00620.

Astronomers have made great strides in discovering planets outside of our solar system, termed “exoplanets.” In fact, over the past 20 years more than 5,000 exoplanets have been detected beyond the eight planets that call our solar system home.

As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases results in a brief brightening of the background star as seen by a telescope. The artistic concept illustrates this effect. This phenomenon of gravitational microlensing enables scientists to search for exoplanets that are too distant and dark to detect any other way.

Credits: NASA Ames/JPL-Caltech/T. Pyle

The majority of these exoplanets have been found snuggled up to their host star completing an orbit (or year) in hours, days or weeks, while some have been found orbiting as far as Earth is to the sun, taking one-Earth-year to circle. But, what about those worlds that orbit much farther out, such as Jupiter and Saturn, or, in some cases, free-floating exoplanets that are on their own and have no star to call home? In fact, some studies suggest that there may be more free-floating exoplanets than stars in our galaxy.

This week, NASA's K2 mission, the repurposed mission of the Kepler space telescope, and other ground-based observatories have teamed up to kick-off a global experiment in exoplanet observation. Their mission: survey millions of stars toward the center of our Milky Way galaxy in search of distant stars' planetary outposts and exoplanets wandering between the stars.

While today's planet-hunting techniques have favored finding exoplanets near their sun, the outer regions of a planetary system have gone largely unexplored. In the exoplanet detection toolkit, scientists have a technique well suited to search these farthest outreaches and the space in between the stars. This technique is called gravitational microlensing.

Gravitational Microlensing

For this experiment, astronomers rely on the effect of a familiar fundamental force of nature to help detect the presence of these far out worlds— gravity. The gravity of massive objects such as stars and planets produces a noticeable effect on other nearby objects.

But gravity also influences light, deflecting or warping, the direction of light that passes close to massive objects. This bending effect can make gravity act as a lens, concentrating light from a distant object, just as a magnifying glass can focus the light from the sun. Scientists can take advantage of the warping effect by measuring the light of distant stars, looking for a brightening that might be caused by a massive object, such as a planet, that passes between a telescope and a distant background star. Such a detection could reveal an otherwise hidden exoplanet.

"The chance for the K2 mission to use gravity to help us explore exoplanets is one of the most fantastic astronomical experiments of the decade," said Steve Howell, project scientist for NASA's Kepler and K2 missions at NASA’s Ames Research Center in California's Silicon Valley. "I am happy to be a part of this K2 campaign and look forward to the many discoveries that will be made."

In a global experiment in exoplanet observation, the K2 mission and Earth-based observatories on six continents will survey millions of stars toward the center of our Milky Way galaxy. Using a technique called gravitational microlensing, scientists will hunt for exoplanets that orbit far from their host star, such as Jupiter is to our sun, and for free-floating exoplanets that wander between the stars. The method allow exoplanets to be found that are up to 10 times more distant than those found by the original Kepler mission, which used the transit technique. The artistic concept illustrates the relative locations of the search areas for NASA's K2 and Kepler missions.

Credits: NASA Ames/W. Stenzel and JPL-Caltech/R. Hurt

This phenomenon of gravitational microlensing – “micro” because the angle by which the light is deflected is small – is the effect for which scientists will be looking during the next three months. As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases results in a brief brightening of the background star as seen by the observatory.

The lensing events caused by a free-floating exoplanet last on the order of a day or two, making the continuous gaze of the Kepler spacecraft an invaluable asset for this technique.

"We are seizing the opportunity to use Kepler's uniquely sensitive camera to sniff for planets in a different way," said Geert Barentsen, research scientist at Ames.

The ground-based observatories will record simultaneous measurements of these brief events. From their different vantage points, space and Earth, the measurements can determine the location of the lensing foreground object through a technique called parallax.

“This is a unique opportunity for the K2 mission and ground-based observatories to conduct a dedicated wide-field microlensing survey near the center of our galaxy," said Paul Hertz, director of the astrophysics division in NASA’s Science Mission Directorate at the agency’s headquarters in Washington. "This first-of-its-kind survey serves as a proof of concept for NASA’s Wide-Field Infrared Survey Telescope (WFIRST), which will launch in the 2020s to conduct a larger and deeper microlensing survey. In addition, because the Kepler spacecraft is about 100 million miles from Earth, simultaneous space- and ground-based measurements will use the parallax technique to better characterize the systems producing these light amplifications."

To understand parallax, extend your arm and hold up your thumb. Close one eye and focus on your thumb and then do the same with the other eye. Your thumb appears to move depending on the vantage point. For humans to determine distance and gain depth perception, the vantage points, our eyes, use parallax.

Flipping the Spacecraft

The Kepler spacecraft trails Earth as it orbits the sun and is normally pointed away from Earth during the K2 mission. But this orientation means that the part of the sky being observed by the spacecraft cannot generally be observed from Earth at the same time, since it is mostly in the daytime sky.

To allow simultaneous ground-based observations, flight operations engineers at Ball Aerospace and the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder will perform a maneuver turning the spacecraft around to point the telescope in the forward velocity vector. So, instead of looking towards where it’s been, the spacecraft will look in the direction of where it’s going.

This alignment will yield a viewing opportunity of Earth and the moon as they cross the spacecraft's field of view. On April 14 at 11:50 a.m. PDT (18:50 UT), Kepler will record a full frame image. The result of that image will be released to the public archive in June once the data has been downloaded and processed. Kepler measures the change in brightness of objects and does not resolve color or physical characteristics of an observed object.

Observing from Earth

To achieve the objectives of this important path-finding research and community exercise in anticipation of WFIRST, approximately two-dozen ground-based observatories on six continents will observe in concert with K2. Each will contribute to various aspects of the experiment and will help explore the distribution of exoplanets across a range of stellar systems and distances.

These results will aid in our understanding of both planetary system architectures as well as the frequency of exoplanets throughout our galaxy.

For a complete list of participating observatories, reference the paper that defines the experiment: Campaign 9 of the K2 mission.

During the roughly 80-day observing period or campaign, astronomers hope to discover over 100 lensing events, ten or more of which may have signatures of exoplanets occupying relatively unexplored regimes of parameter space.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

For more information about the Kepler and K2 missions, visit:

http://www.nasa.gov/kepler

​

The engineers huddled around a telemetry screen, and the mood was tense. They were watching streams of data from a crippled spacecraft more than 50 million miles away – so far that even at the speed of light, it took nearly nine minutes for a signal to travel to the spacecraft and back.

Engineers developed an innovative way to stabilize and control the spacecraft. This technique of using the sun as the "third wheel" has Kepler searching for planets again, but also making discoveries on young stars to supernovae.

Credits: NASA Ames/W Stenzel

Kepler's Second Light: How K2 Works

It was late August 2013, and the group of about five employees at Ball Aerospace in Boulder, Colorado, was waiting for NASA’s Kepler space telescope to reveal whether it would live or die. A severe malfunction had robbed the planet-hunting Kepler of its ability to stay pointed at a target without drifting off course.

The engineers had devised a remarkable solution: using the pressure of sunlight to stabilize the spacecraft so it could continue to do science. Now, there was nothing more they could do but wait for the spacecraft to reveal its fate.

“You’re not watching it unfold in real time,” said Dustin Putnam, Ball’s attitude control lead for Kepler. “You’re watching it as it unfolded a few minutes ago, because of the time the data takes to get back from the spacecraft.”

Finally, the team received the confirmation from the spacecraft they had been waiting for. The room broke out in cheers. The fix worked! Kepler, with a new lease on life, was given a new mission as K2. But the biggest surprise was yet to come. A space telescope with a distinguished history of discovering distant exoplanets – planets orbiting other stars – was about to outdo even itself, racking up hundreds more discoveries and helping to usher in entirely new opportunities in astrophysics research.

“Many of us believed that the spacecraft would be saved, but this was perhaps more blind faith than insight,” said Tom Barclay, senior research scientist and director of the Kepler and K2 guest observer office at NASA’s Ames Research Center in California's Silicon Valley. "The Ball team devised an ingenious solution allowing the Kepler space telescope to shine again."

The discoveries roll in

A little more than two years after the tense moment for the Ball engineers, K2 has delivered on its promise with a breadth of discoveries. Continuing the exoplanet-hunting legacy, K2 has discovered more than three dozen exoplanets and with more than 250 candidates awaiting confirmation. A handful of these worlds are near-Earth-sized and orbit stars that are bright and relatively nearby compared with Kepler discoveries, allowing scientists to perform follow-up studies. In fact, these exoplanets are likely future targets for the Hubble Space Telescope and the forthcoming James Webb Space Telescope (JWST), with the potential to study these planets’ atmospheres in search of signatures indicative of life.

In this artist’s conception, a tiny rocky object vaporizes as it orbits a white dwarf star. Astronomers have detected the first planetary object transiting a white dwarf using data from the K2 mission. Slowly the object will disintegrate, leaving a dusting of metals on the surface of the star.

Credits: CfA/Mark A. Garlick

Dead star devours mini-planet

K2 also has astronomers rethinking long-held planetary formation theory, and the commonly understood lonely "hot Jupiter" paradigm. The unexpected discovery of a star with a close-in Jupiter-sized planet sandwiched between two smaller companion planets now has theorists back at their computers reworking the models, and has sent astronomers back to their telescopes in search of other hot Jupiter companions.

“It remains a mystery how a giant planet can form far out and migrate inward leaving havoc in its wake and still have nearby planetary companions,” said Barclay.

Like its predecessor, K2 searches for planetary transits – the tiny, telltale dip in the brightness of a star as a planet crosses in front – and for the first time caught the rubble from a destroyed exoplanet transiting across the remains of a dead star known as a white dwarf. Exoplanets have long been thought to orbit these remnant stars, but not until K2 has the theory been confirmed.

K2 has fixed its gaze on regions of the sky with densely packed clusters of stars which has revealed the first transiting exoplanet in such an area, popularly known as the Hyades star cluster. Clusters are exciting places to find exoplanets because stars in a cluster all form around the same time, giving them all the same "born-on" date. This helps scientists understand the evolution of planetary systems.

Seventy days worth of solar system observations from K2 are highlighted in this sped-up movie. Neptune, in a dance with its moons, demonstrates the solar system in action. Neptune appears on day 15, followed by its moon Triton, which looks small and faint. Keen-eyed observers can also spot Neptune's tiny moon Nereid at day 24.

Credits: NASA/Ames/SETI/J. Rowe

VIDEO: Neptune Dances with Its Moons

The repurposed spacecraft boasts discoveries beyond the realm of exoplanets. Mature stars – about the age of our sun and older – largely populated the original single Kepler field of view. In contrast, many K2 fields see stars still in the process of forming. In these early days, planets also are assembled and by looking at the timescales of star formation, scientists gain insight into how our own planet formed.

Studies of one star-forming region, called Upper Scorpius, compared the size of young stars observed by K2 with computational models. The result demonstrated fundamental imperfections in the models. While the reason for these discrepancies is still under debate, it likely shows that magnetic fields in stars do not arise as researchers expect.

Looking in the ecliptic – the orbital path traveled around the sun by the planets of our solar system and the location of the zodiac – K2 also is well equipped to observe small bodies within our own solar system such as comets, asteroids, dwarf planets, ice giants and moons. Last year, for instance, K2 observed Neptune in a dance with its two moons, Triton and Nereid. This was followed by observations of Pluto and Uranus.

“K2 can’t help but observe the dynamics of our planetary system, " said Barclay. "We all know that planets follow laws of motion but with K2 we can see it happen.”

These initial accomplishments have come in the first year and a half since K2 began in May 2014, and have been carried off without a hitch. The spacecraft continues to perform nominally.

Searching for far out worlds

In April, K2 will take part in a global experiment in exoplanet observation with a special observing period or campaign, Campaign 9. In this campaign, both K2 and astronomers at ground-based observatories on five continents will simultaneously monitor the same region of sky towards the center of our galaxy to search for small planets, such as the size of Earth, orbiting very far from their host star or, in some cases, orbiting no star at all.

For this experiment, scientists will use gravitational microlensing – the phenomenon that occurs when the gravity of a foreground object, such as a planet, focuses and magnifies the light from a distant background star. This detection method will allow scientists to find and determine the mass of planets that orbit at great distances, like Jupiter and Neptune do our sun.

At the first K2 Science Conference in Nov. 2015, nearly 200 scientists from around the world convened to discuss their research using K2 data. Knicole Colon, K2 support scientist, walks through the K2 observing opportunities available to the science community. To date, nearly 800 scientists have authored more than 100 scientific papers using K2 data.

Credits: Michele Johnson/NASA Ames

Design by community

What could turn out to be one of the most important legacies of K2 has little to do with the mechanics of the telescope, now operating on two wheels and with an assist from the sun.

The Kepler mission was organized along traditional lines of scientific discovery: a targeted set of objectives carefully chosen by the science team to answer a specific question on behalf of NASA – how common or rare are "Earths" around other suns?

K2’s modified mission involves a whole new approach-- engaging the scientific community at large and opening up the spacecraft's capabilities to a broader audience.

"The new approach of letting the community decide the most compelling science targets we’re going to look at has been one of the most exciting aspects," said Steve Howell, the Kepler and K2 project scientist at Ames. "Because of that, the breadth of our science is vast, including star clusters, young stars, supernovae, white dwarfs, very bright stars, active galaxies and, of course, exoplanets.”

In the new paradigm, the K2 team laid out some broad scientific objectives for the mission and planned to operate the spacecraft on behalf of the community. 

Kepler’s field of view surveyed just one patch of sky in the northern hemisphere. The K2 ecliptic field of view provides greater opportunities for Earth-based observatories in both the northern and southern hemispheres, allowing the whole world to participate.

With more than two years of fuel remaining, the spacecraft’s scientific future continues to look unexpectedly bright.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

For more information about the Kepler and K2 missions, visit:

http://www.nasa.gov/kepler

Authored by Michele Johnson and H. Pat Brennan/JPL

Scientists using NASA’s repurposed Kepler space telescope, known as the K2 mission, have uncovered strong evidence of a tiny, rocky object being torn apart as it spirals around a white dwarf star. This discovery validates a long-held theory that white dwarfs are capable of cannibalizing possible remnant planets that have survived within its solar system.

“We are for the first time witnessing a miniature “planet” ripped apart by intense gravity, being vaporized by starlight and raining rocky material onto its star,” said Andrew Vanderburg, graduate student from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and lead author of the paper published in Nature.

In this artist’s conception, a tiny rocky object vaporizes as it orbits a white dwarf star. Astronomers have detected the first planetary object transiting a white dwarf using data from the K2 mission. Slowly the object will disintegrate, leaving a dusting of metals on the surface of the star.

Credits: CfA/Mark A. Garlick

As stars like our sun age, they puff up into red giants and then gradually lose about half their mass, shrinking down to 1/100^th of their original size to roughly the size of Earth. This dead, dense star remnant is called a white dwarf.

The devastated planetesimal, or cosmic object formed from dust, rock, and other materials, is estimated to be the size of a large asteroid, and is the first planetary object to be confirmed transiting a white dwarf. It orbits its white dwarf, WD 1145+017, once every 4.5 hours. This orbital period places it extremely close to the white dwarf and its searing heat and shearing gravitational force.

During its first observing campaign from May 30, 2014 to Aug. 21, 2014, K2 trained its gaze on a patch of sky in the constellation Virgo, measuring the minuscule change in brightness of the distant white dwarf. When an object transits or passes in front of a star from the vantage point of the space telescope, a dip in starlight is recorded. The periodic dimming of starlight indicates the presence of an object in orbit about the star.

The diagram depicts a model of light curve shapes. The red line indicates the symmetric shape of a hypothetical Earth-size planet transit while the blue line is the asymmetric shape of the tiny disintegrating planet and its comet-like trailing dusty tail. The black dots are measurements recorded by the K2 mission of WD 1145+017.

Credits: CfA/A. Vanderburg

A research team led by Vanderburg found an unusual, but vaguely familiar pattern in the data. While there was a prominent dip in brightness occurring every 4.5 hours, blocking up to 40 percent of the white dwarf's light, the transit signal of the tiny planet did not exhibit the typical symmetric U-shaped pattern. It showed an asymmetric elongated slope pattern that would indicate the presence of a comet-like tail. Together these features indicated a ring of dusty debris circling the white dwarf, and what could be the signature of a small planet being vaporized.

“The eureka moment of discovery came on the last night of observation with a sudden realization of what was going around the white dwarf. The shape and changing depth of the transit were undeniable signatures,” said Vanderburg.

In addition to the strangely shaped transits, Vanderburg and his team found signs of heavier elements polluting the atmosphere of WD 1145+017, as predicted by theory.

Due to intense gravity, white dwarfs are expected to have chemically pure surfaces, covered only with light elements of helium and hydrogen. For years, researchers have found evidence that some white dwarf atmospheres are polluted with traces of heavier elements such as calcium, silicon, magnesium and iron. Scientists have long suspected that the source of this pollution was an asteroid or a small planet being torn apart by the white dwarf's intense gravity.

Analysis of the star's atmospheric composition was conducted using observations made by the University of Arizona's MMT Observatory. 

“For the last decade we’ve suspected that white dwarf stars were feeding on the remains of rocky objects, and this result may be the smoking gun we’re looking for,” said Fergal Mullally, staff scientist of K2 at SETI and NASA’s Ames Research Center in Moffett Field, California. “However, there's still a lot more work to be done figuring out the history of this system.”

“This discovery highlights the power and serendipitous nature of K2. The science community has full access to K2 observations and is using these data to make a wide range of unique discoveries across the full range of astrophysics phenomena,” said Steve Howell, K2 project scientist at Ames.

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

For more information about the Kepler and K2 missions, visit:

http://www.nasa.gov/kepler

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