astronomical data

Cassini obtains clearest-ever view of Saturn’s pierogi-shaped moon Pan.

Cassini flew to within 15,000 miles of Saturn’s tiny moon Pan March 7 and obtained the clearest pictures yet taken of the satellite.

Measuring only 21 miles long by 12 miles wide, Pan orbits in the Encke Gap of Saturn’s A-ring. Pan’s existence was theorized in the late 1980s by astronomers reanalyzing data from the 1981 Voyager 2 flyby of Saturn and officially confirmed in 1990. Up until this year, only lower-resolution images of Pan from further away were obtained.

Cassini is scheduled to end its mission September 15 when it will plunge into the planet’s atmosphere.

The Easterbunny Comes to NGC 4725 : At first called Easterbunny by its discovery team, officially named Makemake is the second brightest dwarf planet of the Kuiper belt. The icy world appears twice in this astronomical image, based on data taken on June 29 and 30 of the bright spiral galaxy NGC 4725. Makemake is marked by short red lines, its position shifting across a homemade telescopes field-of-view over two nights along a distant orbit. On those dates nearly coincident with the line-of-sight to the spiral galaxy in the constellation Coma Berenices, Makemake was about 52.5 astronomical units or 7.3 light-hours away. NGC 4725 is over 100,000 light-years across and 41 million light-years distant. Makemake is now known to have at least one moon. NGC 4725 is a famous one-armed spiral galaxy. via NASA

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Nothing Escapes From A Black Hole, And Now Astronomers Have Proof

“Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we’ve expected for decades. General Relativity has passed another critical test.”

Are event horizons real? With data taken from around a dozen observatories earlier this year, simultaneously, the Event Horizon Telescope is poised to put together the first-ever direct image of the black hole at the center of our galaxy Sagittarius A*. If event horizons are real, this data should be able to create the first-ever image of it, proving that nothing escapes from inside a black hole once you’ve been swallowed. But why wait? Through a very clever technique, a team of astronomers used data from the Pan-STARRS telescope to test the alternative: that there’d be a hard surface exterior to where the event horizon is supposed to be. If that were the case, stars that collided with these hard surfaces would create a transient signal in the visible and infrared, which is exactly what Pan-STARRS is sensitive to.

The lack of such signals, even though a significant number would be expected, shows that the alternative to event horizons cannot stand. Event horizons are real, and now we have indirect proof!

Intergalactic gas and ripples in the cosmic web

The most barren regions known are the far-flung corners of intergalactic space. In these vast expanses between the galaxies there is just one solitary atom per cubic meter – a diffuse haze of hydrogen gas left over from the Big Bang. On the largest scales, this material is arranged in a vast network of filamentary structures known as the “cosmic web,” its tangled strands spanning billions of light years and accounting for the majority of atoms in the universe.

Now, a team of astronomers, including UC Santa Barbara physicist Joseph Hennawi, have made the first measurements of small-scale ripples in this primeval hydrogen gas using rare double quasars. Although the regions of cosmic web they studied lie nearly 11 billion light years away, they were able to measure variations in its structure on scales 100,000 times smaller, comparable to the size of a single galaxy. The results appear in the journal Science.

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IceCube helps demystify strange radio bursts from deep space

For a decade, astronomers have puzzled over ephemeral but incredibly powerful radio bursts from space.

The phenomena, known as fast radio bursts or FRBs, were first detected in 2007 by astronomers scouring archival data from Australia’s Parkes Telescope, a 64-meter diameter dish best known for its role receiving live televison images from the Apollo 11 moon landing in 1969.

But the antenna’s detection of the first FRB – and the subsequent confirmed discovery of nearly two dozen more powerful radio pulses across the sky by Parkes and other radio telsescopes – has sent astrophysicists scurrying to find more of the objects and to explain them.

“It’s a new class of astronomical events. We know very little about FRBs in general,” explains Justin Vandenbroucke, a University of Wisconsin-Madison physicist who, with his colleagues, is turning IceCube, the world’s most sensitive neutrino telescope, to the task of helping demystify the powerful pulses of radio energy generated up to billions of light-years from Earth.

The idea, the Wisconsin physicist says, is to see if high-energy neutrinos are generated coincident with FRBs. If that’s the case, it would give scientists leads to what might be generating the powerful radio flares and reveal something about the physics of the environments where they are generated.

IceCube is a neutrino detector composed of 5,160 optical modules embedded in a gigaton of crystal-clear ice a mile beneath the geographic South Pole. Supported by the National Science Foundation, IceCube is capable of capturing the fleeting signatures of high-energy neutrinos – nearly massless particles generated, presumably, by dense, violent objects such as supermassive black holes, galaxy clusters, and the energetic cores of star-forming galaxies.

The catch with fast radio bursts, notes Vandenbroucke, is that they are mostly random and they last for only a few milliseconds, too fast to routinely detect or conduct follow-up observations with radio and optical telescopes. Only one FRB has been found to repeat, an object known as FRB 121102 in a galaxy about 3 billion light-years away. A key advantage of IceCube is the telescope’s extremely wide field of view compared to optical and radio telescopes. The telescope gathers data on neutrino events as the particles crash through the Earth, and it sees the entire sky in both the southern and northern hemispheres.

That means if an FRB is detected by any of the world’s radio telescopes, Vandenbroucke and his team can analyze IceCube data for that region of the sky at the time the radio pulse was detected.

Observing a fast radio burst in conjunction with neutrinos would be a coup, helping establish source objects for both types of phenomena. “Astrophysical neutrinos and fast radio bursts are two of the most exciting mysteries in physics today,” says Vandenbroucke. “There may be a link between them.”

So far, Vandenbroucke and his team have looked at nearly 30 FRBs, including 17 bursts from the “repeater,” FRB 121102.

The UW team’s first look, however, did not detect neutrino emission with any of the FRBs identified in IceCube’s archival data. Not seeing neutrinos in concert with any of the FRBs studied so far gives scientists an upper limit on the amount of neutrino emission that could occur in a burst.

“We can say that the amount of energy emitted by each burst as neutrinos is less than a certain amount, which can then be compared to predictions from individual theories,” Vandenbroucke explains. “As the number of bursts is expected to grow dramatically in the next couple years, these constraints will become even stronger – or we will make a detection.”

Bright or very high-energy neutrinos would be characteristic of certain classes of astronomical objects. “We’ve ruled out gamma-ray bursts and we’ve strongly constrained the possibility of black holes” as neutrino sources, says Vandenbroucke. His team’s analysis of four FRB events was published in the August 2017 Astrophysical Journal. “There could be even more exotic physics going on.”

Scientists believe FRBs occur much more frequently than they have been observed. Some estimate that there are as many as 10,000 FRB events per day coming from all directions in the sky. And with astronomers now on the lookout for the starnge pulses of radio energy, Vandenbroucke expects the pace of discovery to accelerate as the world’s radio telescopes continue their searches and as new radio interferometers come on line.

IMAGE….IceCube is a neutrino detector composed of 5,160 optical modules embedded in a gigaton of crystal-clear ice a mile beneath the geographic South Pole. PHOTO COURTESY OF NATIONAL SCIENCE FOUNDATION

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Pan-STARRS solves the biggest problem facing every astronomer

“The science that came out of it alone is staggering. Nobody has had as much astronomical data in all of history as what Pan-STARRS has produced. They’ve discovered about 3,000 new near-Earth objects; tens of thousands of asteroids in the main belt, approximately 300 Kuiper belt objects (about a third of all the Kuiper belt objects ever discovered), and imaged a total of more than three billion verified objects. For those of you wondering, there’s no evidence for or against Planet Nine in the data, but the Pan-STARRS data does support that our Solar System ejected a fifth gas giant in its distant past.”

If you want to observe the night sky, it’s not quite as simple as pointing your telescope and collecting photons. You have to calibrate your data, otherwise your interpretation of what you’re looking at could be skewed by gas, dust, the atmosphere or other intervening factors that you’ve failed to consider. Without a proper calibration, you don’t know how reliable what you’re looking at is. The previous best calibration was the Digitized Sky Survey 2, which went down to 13 millimagnitudes, or an accuracy of 1.2%. Just a few weeks ago, Pan-STARRS released the largest astronomy survey results of all-time: 2 Petabytes of data. It quadruples the accuracy of every calibration we’ve ever had, and that’s before you even get into the phenomenal science it’s uncovered.

Come learn how it’s solved the biggest problem facing every astronomer, and why observational astronomy will never be the same!

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Hubble captures ‘shadow play’ caused by possible planet

Searching for planets around other stars is a tricky business. They’re so small and faint that it’s hard to spot them. But a possible planet in a nearby stellar system may be betraying its presence in a unique way: by a shadow that is sweeping across the face of a vast pancake-shaped gas-and-dust disk surrounding a young star.

The planet itself is not casting the shadow. But it is doing some heavy lifting by gravitationally pulling on material near the star and warping the inner part of the disk. The twisted, misaligned inner disk is casting its shadow across the surface of the outer disk.

These images, taken a year apart by NASA’s Hubble Space Telescope, reveal a shadow moving counterclockwise around a gas-and-dust disk encircling the young star TW Hydrae. The two images at the top, taken by the Space Telescope Imaging Spectrograph, show an uneven brightness across the disk.

Through enhanced image processing (images at bottom), the darkening becomes even more apparent. These enhanced images allowed astronomers to determine the reason for the changes in brightness.

The dimmer areas of the disk, at top left, are caused by a shadow spreading across the outer disk. The dotted lines approximate the shadow’s coverage. The long arrows show how far the shadow has moved in a year (from 2015-2016), which is roughly 20 degrees.

Based on Hubble archival data, astronomers determined that the shadow completes a rotation around the central star every 16 years.

They know the feature is a shadow because dust and gas in the disk do not orbit the star nearly that quickly.

So, the feature must not be part of the physical disk.

The shadow may be caused by the gravitational effect of an unseen planet orbiting close to the star. The planet pulls up material from the main disk, creating a warped inner disk. The twisted disk blocks light from the star and casts a shadow onto the disk’s outer region.

A team of astronomers led by John Debes of the Space Telescope Science Institute in Baltimore, Maryland say this scenario is the most plausible explanation for the shadow they spotted in the stellar system TW Hydrae, located 192 light-years away in the constellation Hydra, also known as the Female Water Snake. The star is roughly 8 million years old and slightly less massive than our sun. Debes’ team uncovered the phenomenon while analyzing 18 years’ worth of archival observations taken by NASA’s Hubble Space Telescope.

“This is the very first disk where we have so many images over such a long period of time, therefore allowing us to see this interesting effect,” Debes said. “That gives us hope that this shadow phenomenon may be fairly common in young stellar systems.”

Debes will present his team’s results Jan. 7 at the winter meeting of the American Astronomical Society in Grapevine, Texas.

Debes’ first clue to the phenomenon was a brightness in the disk that changed with position. Astronomers using Hubble’s Space Telescope Imaging Spectrograph (STIS) first noted this brightness asymmetry in 2005. But they had only one set of observations, and could not make a definitive determination about the nature of the mystery feature.

Searching the archive, Debes’ team put together six images from several different epochs. The observations were made by STIS and by the Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS).

STIS is equipped with a coronagraph that blocks starlight to within about 1 billion miles from the star, allowing Hubble to look as close to the star as Saturn is to our sun. Over time, the structure appeared to move in counter-clockwise fashion around the disk, until, in 2016, it was in the same position as it was in images taken in 2000.

This 16-year period puzzled Debes. He originally thought the feature was part of the disk, but the short period meant that the feature was moving way too fast to be physically in the disk. Under the laws of gravity, disks rotate at glacial speeds. The outermost parts of the TW Hydrae disk would take centuries to complete one rotation.

“The fact that I saw the same motion over 10 billion miles from the star was pretty significant, and told me that I was seeing something that was imprinted on the outer disk rather than something that was happening directly in the disk itself,” Debes said. “The best explanation is that the feature is a shadow moving across the surface of the disk.”

Debes concluded that whatever was making the shadow must be deep inside the 41-billion-mile-wide disk, so close to the star it cannot be imaged by Hubble or any other present-day telescope.

The most likely way to create a shadow is to have an inner disk that is tilted relative to the outer disk. In fact, submillimeter observations of TW Hydrae by the Atacama Large Millimeter Array (ALMA) in Chile suggested a possible warp in the inner disk.

But what causes disks to warp? “The most plausible scenario is the gravitational influence of an unseen planet, which is pulling material out of the plane of the disk and twisting the inner disk,” Debes explained. “The misaligned disk is inside the planet’s orbit.”

Given the relatively short 16-year period of the clocklike moving shadow, the planet is estimated to be about 100 million miles from the star – about as close as Earth is from the sun. The planet would be roughly the size of Jupiter to have enough gravity to pull the material up out of the plane of the main disk. The planet’s gravitational pull causes the disk to wobble, or precess, around the star, giving the shadow its 16-year rotational period.

Recent observations of TW Hydrae by ALMA in Chile add credence to the presence of a planet. ALMA revealed a gap in the disk roughly 93 million miles from TW Hydrae. A gap is significant, because it could be the signature of an unseen planet clearing away a path in the disk.

This new Hubble study, however, offers a unique way to look for planets hiding in the inner part of the disk and probe what is happening very close to the star, which is not reachable in direct imaging by current telescopes. “What is surprising is that we can learn something about an unseen part of the disk by studying the disk’s outer region and by measuring the motion, location, and behavior of a shadow,” Debes said.

“This study shows us that even these large disks, whose inner regions are unobservable, are still dynamic, or changing in detectable ways which we didn’t imagine.”

TOP IMAGES….These images, taken a year apart by NASA’s Hubble Space Telescope, reveal a shadow moving counterclockwise around a gas-and-dust disk encircling the young star TW Hydrae. The two images at the top, taken by the Space Telescope Imaging Spectrograph, show an uneven brightness across the disk. Through enhanced image processing (images at bottom), the darkening becomes even more apparent. These enhanced images allowed astronomers to determine the reason for the changes in brightness. The dimmer areas of the disk, at top left, are caused by a shadow spreading across the outer disk. The dotted lines approximate the shadow’s coverage. The long arrows show how far the shadow has moved in a year (from 2015-2016), which is roughly 20 degrees. Based on Hubble archival data, astronomers determined that the shadow completes a rotation around the central star every 16 years. They know the feature is a shadow because dust and gas in the disk do not orbit the star nearly that quickly. So, the feature must not be part of the physical disk. The shadow may be caused by the gravitational effect of an unseen planet orbiting close to the star. The planet pulls up material from the main disk, creating a warped inner disk. The twisted disk blocks light from the star and casts a shadow onto the disk’s outer region. Credit NASA, ESA, and J. Debes (STScI)


LOWER IMAGE….This diagram reveals the proposed structure of a gas-and-dust disk surrounding the nearby, young star TW Hydrae.The illustration shows an inner disk that is tilted due to the gravitational influence of an unseen companion, which is orbiting just outside the disk.The tilted inner disk is the best explanation for a shadow covering part of the disk’s outer region. The warped disk is blocking light from the star and casting the shadow across the disk. The nature of the darkening was first revealed in Hubble Space Telescope archival observations, which showed that the feature moved around the star at a much faster rate than any phenomenon that would be physically linked to the slowly rotating disk.TW Hydrae is about 8 million years old and resides 192 light-years from Earth. Credit NASA, ESA, and A. Feild (STScI)

  • The Whirlpool Galaxy 51 is a popular target for professional astronomers, who study it to further understand galaxy structure particularly structure associated with the spiral arms and galaxy interactions.
  • This image is part of a “quartet of galaxies” collaboration of professional and amateur astronomers that combines optical data from amateur telescopes with data from the archives of NASA missions.
NASA’s Fleet of Planet-hunters and World-explorers

Around every star there could be at least one planet, so we’re bound to find one that is rocky, like Earth, and possibly suitable for life. While we’re not quite to the point where we can zoom up and take clear snapshots of the thousands of distant worlds we’ve found outside our solar system, there are ways we can figure out what exoplanets light years away are made of, and if they have signs of basic building blocks for life. Here are a few current and upcoming missions helping us explore new worlds:

Kepler

Launched in 2009, the Kepler space telescope searched for planets by looking for telltale dips in a star’s brightness caused by crossing, or transiting, planets. It has confirmed more than 1,000 planets; of these, fewer than 20 are Earth-size (therefore possibly rocky) and in the habitable zone – the area around a star where liquid water could pool on the surface of an orbiting planet. Astronomers using Kepler data found the first Earth-sized planet orbiting in the habitable zone of its star and one in the habitable zone of a sun-like star.

In May 2013, a second pointing wheel on the spacecraft broke, making it not stable enough to continue its original mission. But clever engineers and scientists got to work, and in May 2014, Kepler took on a new job as the K2 mission. K2 continues the search for other worlds but has introduced new opportunities to observe star clusters, young and old stars, active galaxies and supernovae.

Transiting Exoplanet Survey Satellite (TESS)

Revving up for launch around 2017-2018, NASA’s Transiting Exoplanet Survey Satellite (TESS) will find new planets the same way Kepler does, but right in the stellar backyard of our solar system while covering 400 times the sky area. It plans to monitor 200,000 bright, nearby stars for planets, with a focus on finding Earth and Super-Earth-sized planets. 

Once we’ve narrowed down the best targets for follow-up, astronomers can figure out what these planets are made of, and what’s in the atmosphere. One of the ways to look into the atmosphere is through spectroscopy.  

As a planet passes between us and its star, a small amount of starlight is absorbed by the gas in the planet’s atmosphere. This leaves telltale chemical “fingerprints” in the star’s light that astronomers can use to discover the chemical composition of the atmosphere, such as methane, carbon dioxide, or water vapor. 

James Webb Space Telescope

Launching in 2018, NASA’s most powerful telescope to date, the James Webb Space Telescope (JWST), will not only be able to search for planets orbiting distant stars, its near-infrared multi-object spectrograph will split infrared light into its different colors- spectrum- providing scientists with information about an physical properties about an exoplanet’s atmosphere, including temperature, mass, and chemical composition. 

Hubble Space Telescope

Hubble Space Telescope is better than ever after 25 years of science, and has found evidence for atmospheres bleeding off exoplanets very close to their stars, and even provided thermal maps of exoplanet atmospheres. Hubble holds the record for finding the farthest exoplanets discovered to date, located 26,000 light-years away in the hub of our Milky Way galaxy.

Chandra X-ray Observatory

Chandra X-ray Observatory can detect exoplanets passing in front of their parent stars. X-ray observations can also help give clues on an exoplanet’s atmosphere and magnetic fields. It has observed an exoplanet that made its star act much older than it actually is

Spitzer Space Telescope

Spitzer Space Telescope has been unveiling hidden cosmic objects with its dust-piercing infrared vision for more than 12 years. It helped pioneer the study of atmospheres and weather on large, gaseous exoplanets. Spitzer can help narrow down the sizes of exoplanets, and recently confirmed the closest known rocky planet to Earth.

SOFIA

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airplane mounted with an infrared telescope that can fly above more than 99 percent of Earth’s atmospheric water vapor. Unlike most space observatories, SOFIA can be routinely upgraded and repaired. It can look at planetary-forming systems and has recently observed its first exoplanet transit

What’s Coming Next?

Analyzing the chemical makeup of Earth-sized, rocky planets with thin atmospheres is a big challenge, since smaller planets are incredibly faint compared to their stars. One solution is to block the light of the planets’ glaring stars so that we can directly see the reflected light of the planets. Telescope instruments called coronagraphs use masks to block the starlight while letting the planet’s light pass through. Another possible tool is a large, flower-shaped structure known as the starshade. This structure would fly in tandem with a space telescope to block the light of a star before it enters the telescope. 

All images (except SOFIA) are artist illustrations.

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Supermassive Black Hole Has Major Flare

Nothing  escapes a Black Hole, not even light itself, right? Well…

New observations from NASA’s two space telescopes Swift and the Nuclear Spectroscopic Telescope Array (NuSTAR) caught a supermassive black hole in the midst of a giant eruption of X-ray light, helping astronomers address an ongoing puzzle: How do supermassive black holes flare?

The results suggest that supermassive black holes send out beams of X-rays when their surrounding coronas – sources of extremely energetic particles – shoot, or launch, away from the black holes.

“This is the first time we have been able to link the launching of the corona to a flare,” said Dan Wilkins of Saint Mary’s University in Halifax, Canada, lead author of a new paper on the results appearing in the Monthly Notices of the Royal Astronomical Society. “This will help us understand how supermassive black holes power some of the brightest objects in the universe.”

Supermassive black holes don’t give off any light themselves, but they are often encircled by disks of hot, glowing material. The gravity of a black hole pulls swirling gas into it, heating this material and causing it to shine with different types of light. Another source of radiation near a black hole is the corona. Coronas are made up of highly energetic particles that generate X-ray light, but details about their appearance, and how they form, are unclear.

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The Hubble Space Telescope Turns 25!

Hubble scientists released this image of the star cluster Westerlund 2 to celebrate the telescope’s anniversary. ©NASA/ESA

Friday, April 24 marks the 25thanniversary of the Hubble Space Telescope. In its quarter-century of operation, Hubble has broadened our understanding of the cosmos like no instrument before it. To mark the occasion, we spoke with Department of Astrophysics Curator Dr. Michael Shara  who worked with the Hubble mission during his time at the Space Telescope Science Institute. Dr. Shara and his collaborators have logged over 1000 hours using the telescope for their work on star clusters, novae and supernovae.

Department of Astrophysics Curator Dr. Michael Shara. AMNH/D.Finnin

What did your work with the Hubble Space Telescope entail?

I joined the Space Telescope Science Institute (STSI) in 1982, eight years before the launch of Hubble. I was the project manager for the Guide Star Catalog that is used to target and calibrate the Hubble, and a few years after the telescope was launched, I was responsible for overseeing the peer review committees, which looked over proposals from researchers who wanted to use the telescope.

What was that experience like?

It was amazing to be able to see things coming in astronomy years before they were published. Reading hundreds of proposals and sitting in on deliberations about them was spectacular to watch.

How does it feel to look back on the launch of Hubble, twenty-five years out?

This anniversary is a joyous thing. Watching the deployment of Hubble in 1990 was an amazing, heart-stopping experience.

The so-called Pillars of Creation are one of the most iconic images Hubble has captured. ©NASA/ESA

Hubble’s mission didn’t start out exactly as planned, though, did it?

The first three years were bumpy. When word came back that spherical aberration was preventing Hubble from focusing properly, I think everyone working on the project had the same terrible feeling in the pit of their stomachs. The mission to repair it in 1993 was even more tense than the initial launch, but it was wildly successful, and for the last 22 years, the story of Hubble has been one triumph after another.

What are some things that stand out in Hubble’s history?

It’s hard to pick one, because Hubble has just been a discovery machine. It’s the most productive telescope in history, with thousands of refereed papers published using Hubble data so far. One that stands out is the discovery of dark energy by groups using the Hubble. That was a totally unexpected discovery that essentially lobbed a hand grenade into the world of modern physics.

We also learned much  about our own solar system. For example, we saw a comet smash into Jupiter, which helped us understand how frequently these events occur, and what an important role they have played in the development of our solar system.

What makes Hubble such a “discovery machine?”

Part of it is the Hubble Archives. Every image, every spectrum, and every measurement that Hubble takes is stored by STSI. That data is proprietary to the researchers who first gathered it for one year. After that period, the information is free and open to other researchers, as well as the general public. That means there are many astronomers using data in ways the people who gathered it could not have foreseen, like using images that looked for a phenomenon known as microlensing in galaxies to find large populations of novae in those same galaxies.

Jupiter’s moon, Io, passes in front of the gas giant, casting a shadow on its surface. ©NASA/ESA

How has this telescope changed since it was first deployed?

Every few years, Hubble has been upgraded, so it is a much more capable instrument today than when it was launched. The cameras are much more sensitive now, and the infrared and ultraviolet capabilities are vastly better than those available just a few years ago.

After 25 years, how much life does Hubble have left?

Well, the instruments, computers, and gyroscopes on Hubble are doing really well. It’s conceivable that it will be useful until 2021 or 2022. After that, because we don’t have a shuttle program to boost it into a higher orbit, Hubble’s orbit will decay to the point where it finally falls to Earth. But the body of data that Hubble has collected is unmatched, and that information will be put to use for decades to come, and maybe even a century from now.

A METHOD TO IMAGE BLACK HOLES

Researchers from MIT’s Computer Science and Artificial Intelligence Laboratory and Harvard University have developed a new algorithm that could help astronomers produce the first image of a black hole.

The algorithm would stitch together data collected from radio telescopes scattered around the globe, under the auspices of an international collaboration called the Event Horizon Telescope. The project seeks, essentially, to turn the entire planet into a large radio telescope dish.

“Radio wavelengths come with a lot of advantages,” says Katie Bouman, an MIT graduate student in electrical engineering and computer science, who led the development of the new algorithm. “Just like how radio frequencies will go through walls, they pierce through galactic dust. We would never be able to see into the center of our galaxy in visible wavelengths because there’s too much stuff in between.”

But because of their long wavelengths, radio waves also require large antenna dishes. The largest single radio-telescope dish in the world has a diameter of 1,000 feet, but an image it produced of the moon, for example, would be blurrier than the image seen through an ordinary backyard optical telescope.

“A black hole is very, very far away and very compact,” Bouman says. “It’s equivalent to taking an image of a grapefruit on the moon, but with a radio telescope. To image something this small means that we would need a telescope with a 10,000-kilometer diameter, which is not practical, because the diameter of the Earth is not even 13,000 kilometers.”

The solution adopted by the Event Horizon Telescope project is to coordinate measurements performed by radio telescopes at widely divergent locations. Currently, six observatories have signed up to join the project, with more likely to follow.

But even twice that many telescopes would leave large gaps in the data as they approximate a 10,000-kilometer-wide antenna. Filling in those gaps is the purpose of algorithms like Bouman’s.

Bouman will present her new algorithm — which she calls CHIRP, for Continuous High-resolution Image Reconstruction using Patch priors — at the Computer Vision and Pattern Recognition conference in June. She’s joined on the conference paper by her advisor, professor of electrical engineering and computer science Bill Freeman, and by colleagues at MIT’s Haystack Observatory and the Harvard-Smithsonian Center for Astrophysics, including Sheperd Doeleman, director of the Event Horizon Telescope project.

Hidden delays

The Event Horizon Telescope uses a technique called interferometry, which combines the signals detected by pairs of telescopes, so that the signals interfere with each other. Indeed, CHIRP could be applied to any imaging system that uses radio interferometry.

Usually, an astronomical signal will reach any two telescopes at slightly different times. Accounting for that difference is essential to extracting visual information from the signal, but the Earth’s atmosphere can also slow radio waves down, exaggerating differences in arrival time and throwing off the calculation on which interferometric imaging depends.

Bouman adopted a clever algebraic solution to this problem: If the measurements from three telescopes are multiplied, the extra delays caused by atmospheric noise cancel each other out. This does mean that each new measurement requires data from three telescopes, not just two, but the increase in precision makes up for the loss of information.

Preserving continuity

Even with atmospheric noise filtered out, the measurements from just a handful of telescopes scattered around the globe are pretty sparse; any number of possible images could fit the data equally well. So the next step is to assemble an image that both fits the data and meets certain expectations about what images look like. Bouman and her colleagues made contributions on that front, too.

The algorithm traditionally used to make sense of astronomical interferometric data assumes that an image is a collection of individual points of light, and it tries to find those points whose brightness and location best correspond to the data. Then the algorithm blurs together bright points near each other, to try to restore some continuity to the astronomical image.

To produce a more reliable image, CHIRP uses a model that’s slightly more complex than individual points but is still mathematically tractable. You could think of the model as a rubber sheet covered with regularly spaced cones whose heights vary but whose bases all have the same diameter.

Fitting the model to the interferometric data is a matter of adjusting the heights of the cones, which could be zero for long stretches, corresponding to a flat sheet. Translating the model into a visual image is like draping plastic wrap over it: The plastic will be pulled tight between nearby peaks, but it will slope down the sides of the cones adjacent to flat regions. The altitude of the plastic wrap corresponds to the brightness of the image. Because that altitude varies continuously, the model preserves the natural continuity of the image.

Of course, Bouman’s cones are a mathematical abstraction, and the plastic wrap is a virtual “envelope” whose altitude is determined computationally. And, in fact, mathematical objects called splines, which curve smoothly, like parabolas, turned out to work better than cones in most cases. But the basic idea is the same.

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Prior knowledge

Finally, Bouman used a machine-learning algorithm to identify visual patterns that tend to recur in 64-pixel patches of real-world images, and she used those features to further refine her algorithm’s image reconstructions. In separate experiments, she extracted patches from astronomical images and from snapshots of terrestrial scenes, but the choice of training data had little effect on the final reconstructions.

Bouman prepared a large database of synthetic astronomical images and the measurements they would yield at different telescopes, given random fluctuations in atmospheric noise, thermal noise from the telescopes themselves, and other types of noise. Her algorithm was frequently better than its predecessors at reconstructing the original image from the measurements and tended to handle noise better. She’s also made her test data publicly available online for other researchers to use.

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How Stellar Stylists Turn Astronomical Data Into Amazing Space Images 

Cassiopeia A is a 330-year-old ball of red-hot gases and space dust. But with the right makeup and some expert attention, this former star can still look positively radiant. When it’s time for Cassiopeia’s close-up, NASA turns to data visualizers, the photo stylists of the astronomy world. These artistes take homely black-and-white images and transform them into jaw-dropping Technicolor portraits that expose the universe in all its glory. Aren’t they creating false standards of interstellar beauty? “We’re trying to present the object as true as we can,” says Robert Hurt, visualization scientist for the Spitzer Space Telescope, who has crafted hundreds of astronomical images. “We don’t want to glamorize the galaxy.” 

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Astronomers using data from NASA’s Kepler mission have discovered a planetary system of five small planets dating back to when the Milky Way galaxy was a youthful two billion years old. The tightly packed system, named Kepler-444, is home to five small planets in very compact orbits. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist’s conception.

Image Credit: Tiago Campante/Peter Devine (ARTIST CONCEPT)

A Spacecraft's Second Life: Our K2 mission

A critical failure that ended one mission has borne an unexpected and an exciting new science opportunity. The Kepler spacecraft, known for finding thousands of planets orbiting other stars, has a new job as the K2 mission.

Like its predecessor, K2 detects the tiny, telltale dips in the brightness of a star as an object passes or transits it, to possibly reveal the presence of a planet. Searching close neighboring stars for near-Earth-sized planets, K2 is finding planets ripe for follow-up studies on their atmospheres and to see what the planet is made of. A step up from its predecessor, K2 is revealing new info on comets, asteroids, dwarf planets, ice giants and moons. It will also provide new insight into areas as diverse as the birth of new stars, how stars explode into spectacular supernovae, and even the evolution of black holes.

K2 is expanding the planet-hunting legacy and has ushered in entirely new opportunities in astrophysics research, yet this is only the beginning.

Searching Nearby for Signs of Life

Image credit: ESO/L. Calçada

Scientists are excited about nearby multi-planet system known as K2-3. This planetary system, discovered by K2, is made of three super-Earth-sized planets orbiting a cool M-star (or red dwarf) 135 light-years away, which is relatively close in astronomical terms. To put that distance into perspective, if the Milky Way galaxy was scaled down to the size of the continental U.S. it would be the equivalent of walking the three-mile long Golden Gate Park in San Francisco, California. At this distance, our other powerful space-investigators – the Hubble Space Telescope and the forthcoming James Webb Space Telescope (JWST) – could study the atmospheres of these worlds in search of chemical fingerprints that could be indicative of life. K2 expects to find a few hundred of these close-by, near-Earth-sized neighbors.

K2 won’t be alone in searching for nearby planets outside our solar system. Revving up for launch around 2017-2018, our Transiting Exoplanet Survey Satellite (TESS) plans to monitor 200,000 close stars for planets, with a focus on finding Earth and Super-Earth-sized planets.

The above image is an artist rendering of Gliese 581, a planetary system representative of K2-3.

Neptune’s Moon Dance

Movie credit: NASA Ames/SETI Institute/J. Rowe

Spying on our neighbors in our own solar system, K2 caught Neptune in a dance with its moons Triton and Nereid. On day 15 (day counter located in the top right-hand corner of the green frame) of the sped-up movie, Neptune appears, followed by its moon Triton, which looks small and faint. Keen-eyed observers can also spot Neptune’s tiny moon Nereid at day 24. Neptune is not moving backward but appears to do so because of the changing position of the Kepler spacecraft as it orbits around the sun. A few fast-moving asteroids make cameo appearances in the movie, showing up as streaks across the K2 field of view. The red dots are a few of the stars K2 examines in its search for transiting planets outside of our solar system. An international team of astronomers is using these data to track Neptune’s weather and probe the planet’s internal structure by studying subtle brightness fluctuations that can only be observed with K2.

Dead Star Devours Planet

Image credit: CfA/Mark A. Garlick

K2 also caught a white dwarf – the dead core of an exploded star –vaporizing a nearby tiny rocky planet. Slowly the planet will disintegrate, leaving a dusting of metals on the surface of the star. This trail of debris blocks a tiny fraction of starlight from the vantage point of the spacecraft producing an unusual, but vaguely familiar pattern in the data. Recognizing the pattern, scientists further investigated the dwarf’s atmosphere to confirm their find. This discovery has helped validate a long-held theory that white dwarfs are capable of cannibalizing possible remnant planets that have survived within its solar system.

Searching for Far Out Worlds

NASA/JPL-Caltech

In April, spaced-based K2 and ground-based observatories on five continents will participate in a global experiment in exoplanet observation and 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 focuses and magnifies the light from a distant background star.

The animation demonstrates the principles of microlensing. The observer on Earth sees the source (distant) star when the lens (closer) star and planet pass through the center of the image. The inset shows what may be seen through a ground-based telescope. The image brightens twice, indicating when the star and planet pass through the observatory’s line of sight to the distant star.

Full microlensing animation available HERE.

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This quartet of galaxies comes from a collaboration of professional and amateur astronomers that combines optical data from amateur telescopes with data from the archives of NASA missions. Starting in the upper left and moving clockwise, the galaxies are M101 (Pinwheel Galaxy), M81, Centaurus A, and M51 (Whirlpool Galaxy). In these images, X-rays from Chandra are in purple, infrared data from Spitzer are red, and the optical data are in red, green, and blue. The two astrophotographers who donated their images for these four images — Detlef Hartmann and Rolf Olsen — used their personal telescopes of 17.5 inches and 10 inches in diameter, respectively.

Image Credit: X-ray: NASA/CXC/SAO; Optical (M101, M81, M51): Detlef Hartmann; Optical (Centaurus A): Rolf Olsen; Infrared: NASA/JPL-Caltech)

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Stellar cannibalism transforms star into brown dwarf

Astronomers have detected a sub-stellar object that used to be a star, after being consumed by its white dwarf companion.

An international team of astronomers made the discovery by observing a very faint binary system, J1433 which is located 730 light-years away. The system consists of a low-mass object - about 60 times the mass of Jupiter - in an extremely tight 78-minute orbit around a white dwarf (the remnant of a star like our Sun).

Due to their close proximity, the white dwarf strips mass from its low-mass companion. This process has removed about 90 per cent of the mass of the companion, turning it from a star into a brown dwarf.

Most brown dwarfs are ‘failed stars’, objects that were born with too little mass to shine brightly by fusing hydrogen in their cores. By contrast, the brown dwarf in this system was born as a full-fledged star, but has been stripped to its current mass by billions of years of stellar cannibalism.

The study, published in the journal Nature, used the X-Shooter instrument at the Very Large Telescope (VLT) in Cerro Paranal, Chile, in order to directly detect and characterise a system that has survived such a traumatic transition.

Lead author Juan Venancio Hernández Santisteban, a PhD student at the University of Southampton, said: “X-Shooter is a unique instrument that can observe astronomical objects simultaneously all the way from the ultraviolet to the infrared. This allowed us to dissect the light of this system and uncover the hidden signal from the faint brown dwarf.

"Our knowledge of binary evolution suggests that, if the companion star can survive the transition, brown dwarfs should be common in this type of system. However, despite several efforts, only a few candidate systems with tentative evidence for brown-dwarf companions had previously been found. Our results now confirm that the successful transformation of a star to a brown dwarf is indeed possible.”

The astronomers also used their data to map the surface temperature across the brown dwarf. This turns out to be non-uniform, since this cool sub-stellar object is strongly irradiated by its much hotter white dwarf companion. The map shows a clear temperature difference between the dayside (the side facing the white dwarf) and the nightside. On average, the difference amounts to 57 degrees Celsius, but the hottest and coldest parts of the brown dwarf’s surface differ by a full 200 degrees Celsius.

Professor Christian Knigge, from the University of Southampton who initiated and supervised the project, said: “The construction of this surface temperature map is a significant achievement. In many giant planets - the so-called 'hot-Jupiters’ - irradiation by the host star completely overwhelms the planet’s internal heat flux. By contrast, internal heat flux and external irradiation are comparable for the brown dwarf in our study. This represents an unexplored regime, making such systems valuable as laboratories for irradiated (sub-) stellar and planetary atmospheres.”

TOP IMAGE….White dwarf (right) stripping mass from the brown dwarf. Credit Rene Breton, University of Manchester.


CENTRE IMAGE….An irradiated brown dwarf donor. Temperature map of J1433. Credit Juan Venancio Hernández Santisteban


LOWER IMAGE….Orbital phase of white dwarf and brown dwarf donor. Credit Juan Venancio Hernández Santisteban

M83 Star Streams
Image Credit & Copyright: R. Gendler, D. Martinez-Delgado (ARI-ZAH, Univ. Heidelberg) D. Malin (AAO), NAOJ, ESO, HLA - Assembly and Processing: Robert Gendler

Big, bright, and beautiful, spiral galaxy M83 lies a mere twelve million light-years away, near the southeastern tip of the very long constellation Hydra. This deep view of the gorgeous island universe includes observations from Hubble, along with ground based data from the European Southern Observatory’s very large telescope units, National Astronomical Observatory of Japan’s Subaru telescope, and Australian Astronomical Observatory photographic data by D. Malin. About 40,000 light-years across, M83 is popularly known as the Southern Pinwheel for its pronounced spiral arms. But the wealth of reddish star forming regions found near the edges of the arms’ thick dust lanes, also suggest another popular moniker for M83, the Thousand-Ruby Galaxy. Arcing near the top of the novel cosmic portrait lies M83’s northern stellar tidal stream, debris from the gravitational disruption of a smaller, merging satellite galaxy. The faint, elusive star stream was found in the mid 1990s by enhancing photographic plates.