Spiral galaxy NGC 3982. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
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Galaxies are like snowflakes, with no two looking exactly the same. The latest image released from the Hubble Space Telescope shows a striking face-on spiral galaxy named NGC 3982, which is a swirl of activity and star birth along with its winding arms. The arms are lined with pink star-forming regions of glowing hydrogen, newborn blue star clusters, and obscuring dust lanes that provide the raw material for future generations of stars. The bright nucleus is home to an older population of stars, which grow ever more densely packed toward the center.
NGC 3982 is located about 68 million light-years away in the constellation Ursa Major. The galaxy spans about 30,000 light-years, one-third of the size of our Milky Way galaxy. This color image is composed of exposures taken by three different instruments, taken over a substantial portion of the space telescope’s life, from March 2000 and August 2009: The Wide Field Planetary Camera 2 (WFPC2), the Advanced Camera for Surveys (ACS), and the Wide Field Camera 3 (WFC3). The observations were taken between The rich color range comes from the fact that the galaxy was photographed in visible and near-infrared light. Also used was a filter that isolates hydrogen emission that emanates from bright star-forming regions dotting the spiral arms.
Every day, I wake up and flip through the titles and abstracts of recent articles posted to arXiv. With increasing regularity, papers pop up announcing the discovery of a new extra-solar planet. At this point, I keep scrolling. How many more hot Jupiters do you really want to hear about? If it’s a record setter in some way, I’ll read it. Another way I’ll pay attention is if there’s reports of detections of spectroscopic detection of components of the atmosphere. While a fistful of transiting planets have had spectral lines discovered, they’re still pretty rare and new discoveries will help constrain our understanding of how planets form.
The holy grail in this field would be to discover elemental signatures of molecules that don’t form naturally and are characteristic of life (as we know it). In 2008, a paper announced the first detection of CO2 in an exoplanet atmosphere (that of HD 189733b), which, although not exclusively, is one of the tracer molecules for life. While HD 189733b isn’t a candidate for searches for ET, it was still a notable first.
Then again, perhaps not. A new study casts doubt on the discovery as well as the report of various molecules in the atmospheres of another exoplanet.
Thus far there have been two methods by which astronomers have attempted to identify molecular species in the atmosphere of exoplanets. The first is by using starlight, filtered by the planet’s atmosphere to search for spectral lines that are only present during transit. The difficulty with this method is that, spreading the light out to detect the spectra weakens the signal, sometimes down to the very point that it’s lost in systematic noise from the telescope itself. The alternative is to use photometric observations, which look at the change in light in different color ranges, to characterize the molecules. Since the ranges are all lumped together, this can improve the signal, but this is a relatively new technique and statistical methodology for this technique is still shaky. Additionally, since only one filter can be used at a time, the observations must generally be taken on different transits, which allow the characteristics of the star to change due to star spots.
The 2008 study by Swain et al. that announced the presence of CO2 used the first of these methods. Their trouble started the following year when a followup study by Sing et al. failed to reproduce the results. In their paper, Sing’s team stated,”Either the planet’s transmission spectrum is variable, or residual systematic errors still plague the edges of the Swain et al. spectrum.”
The new study, by Gibson, Pont, and Aigrain (working from the Universities of Oxford and Exeter) suggests that the claims of Swain’s team were a result of the latter. They suggest that the signal is swamped with more noise than Swain et al. accounted for. This noise comes from the telescope itself (in this case Hubble since these observations would need to be made out of Earth’s atmosphere which would add its own spectral signature). Specifically, they report that since there’s changes in the state of the detector itself that are often hard to identify and correct for, Swain’s team underestimated the error, leading to a false positive. Gibson’s team was able to reproduce the results using Swain’s method, but when they applied a more complete method which didn’t assume that the detector could be calibrated so easily by using observations of the star outside the transit and on different Hubble orbits, the estimation of the errors increased significantly, swamping the signal Swain claimed to have observed.
Gibson’s team also reviewed the case of detections of molecules in the atmosphere of an extra solar planet around XO-1 (on which Tinetti et al. reported to have found methane, water, and CO2). In both cases, they again find that detections of were overstated and the ability to tease signal from the data was dependent on questionable methods.
This week seems to be a bad week for those hoping to find life on extra-solar planets. With this article casting doubt on our ability to detect molecules in distant atmospheres and the recent caution on the detection of Gliese 581g, one might worry about our ability to explore these new frontiers, but what this really underscores is the need to refine our techniques and keep taking deeper looks. This has been a frank reassessment of the current state of knowledge, but does not in any way claim to limit our future discoveries. Additionally, this is how science works; scientists review each others data and conclusions. So, looking on the bright side, science works, even if it’s not exactly telling us what we’d like to hear.
The collision between two asteroids in early 2009 produced a strange, X-shaped aftermath. Image Credit: NASA, ESA and D. Jewitt (UCLA)
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Alas, the image above is not marking alien pirate treasure in space – for the first time, the aftermath of a collision between two asteroids has been imaged. Last January, an international team of astronomers saw the strange X-shaped object with the Hubble Space Telescope after ground-based observatories spotted evidence of an asteroid collision in the asteroid belt. The team has now used Hubble to do follow-up observations and uncovered a few surprises about the collision.
The collision produced an X shape, followed by a long comet-like tail. The astronomers, led by David Jewitt of the University of California in Los Angeles, were surprised to find that the collision did not happen as recently as they’d thought, but had actually occurred almost a year previous to the detection. It’s likely that the two asteroids smashed together sometime in February or March of 2009.
“When I saw the Hubbble image I knew it was something special,” said ESA astronomer Jessica Agarwal in a press release.
Named P/2010 A2, the object is located in the asteroid belt between Mars and Jupiter. Asteroid collisions are thought to be a commonplace occurrence, and are responsible for kicking up dust in our Solar System and other planetary systems. Just how much dust is produced, and how frequent the collisions happen is still a hazy topic, and the recent observation of P/2010 A2 should help astronomers to better model this phenomenon.
By figuring out how much dust is produced by the process of ‘collisional grinding’, astronomers could better model the dusty debris disks of other planetary systems, as well as our own.
The team monitored the slow-motion expansion of the leftovers of the colliding asteroids with the Hubble Space Telescope between January and May of 2010. They’ve determined that P/2010 A2 is about 120 meters (393 feet) wide, and the particles of dust that make up the tail following it are between 1 millimeter (0.04 inches) to 2.5 centimeters (1 inch) in diameter.The collision producing the object P/2010 A2, as observed over the course of a few months by Hubble. Image Credit: NASA, ESA and D. Jewitt (UCLA)
The remnants of the collision suggest that a smaller asteroid – 3 to 5 meters (10-16 feet) wide – collided into a larger one at about 18,000 km per hour (11,000 miles per hour). This vaporized the smaller asteroid, and ejected material from the larger one.
Why is the object X-shaped? That mystery has yet to be determined. It is likely, according to the team, that the filaments produced by the collision suggest asymmetries in the colliding objects. Further observations of P/2010 A2 with the Hubble in 2011 will show just how the collision continues to change, allowing for a more precise model of how it started out.
The observed tail is caused by the same mechanism that produces cometary tails – radiation pressure from the Sun pushes the dust away from the nucleus of the object.
As to why we don’t have thousands of Hubble images to produce a whole alphabet of asteroid collisions shapes – “Catching colliding asteroids on camera is difficult because large impacts are rare, while small ones, such as the one that produced P/2010 A2, are exceedingly faint,” Jewitt said. The results of their observations will be published in the October 14th issue of the journal Nature.
A diagram of the evolution of the universe from the big bang to the present, with two epochs of reionization. Credit: NASA, ESA, and A. Feild (STScI)
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Using Hubble’s newest tool, the Cosmic Origins Spectrograph (COS), researchers have nailed down and enhanced our understanding of the reionization of helium in the early Universe, clarifying the time frame of 11.7 to 11.3 billion years ago when the universe stripped electrons off from primeval helium atoms. Hubble scientists say it was the equivalent of global warming, except that a heat wave blasted through the entire early universe at that time, inhibiting the growth of small galaxies for almost 500 million years.
The universe went through an initial heat wave over 13 billion years ago when energy from early massive stars ionized cold interstellar hydrogen from the Big Bang. This epoch is actually called reionization because the hydrogen nuclei were originally in an ionized state shortly after the Universe’s beginnings.
It took another 2 billion years before the universe produced sources of ultraviolet radiation with enough energy to reionize the helium produced in the Big Bang, which heated intergalactic gas and inhibited it from gravitationally collapsing to form new generations of stars in some small galaxies. The lowest-mass galaxies were not even able to hold onto their gas, and it escaped back into intergalactic space.
This radiation didn’t come from stars, but rather from quasars, the brilliant cores of active galaxies. In fact the epoch when the helium was being reionized corresponds to a transitory time in the universe’s history when quasars were most abundant.
his ultraviolet-light data from the Hubble Space Telescope's Cosmic Origins Spectrograph shows strong helium II absorption and transmission lines from a quasar, identifying an era 11.7 to 11.3 billion years ago when electrons were stripped from primeval helium atoms — a process called reionization. Credit: Shull et al.,
Michael Shull of the University of Colorado and his team were able to find the telltale helium spectral absorption lines in the ultraviolet light from a quasar. The quasar beacon shines light through intervening clouds of otherwise invisible gas, like a headlight shining through a fog. The beam allows for a core-sample probe of the clouds of gas interspersed between galaxies in the early universe.
It was a raucous time. Galaxies frequently collided, and this engorged supermassive black holes in the cores of galaxies with infalling gas. The black holes furiously converted some of the gravitational energy of this mass to powerful far-ultraviolet radiation that would blaze out of galaxies. This heated the intergalactic helium from 18,000 degrees Fahrenheit to nearly 40,000 degrees. After the helium was reionized in the universe, intergalactic gas again cooled down and dwarf galaxies could resume normal assembly.
“I imagine quite a few more dwarf galaxies may have formed if helium reionization had not taken place,” said Shull.
So far Shull and his team only have one sightline to measure the helium transition, but the COS science team plans to use Hubble to look in other directions to see if the helium reionization uniformly took place across the universe.
The science team’s results will be published in the October 20 issue of The Astrophysical Journal.
Dust Pillars in the Carina Nebula. Astronomers are peering inside Carina's pillars to get new details about starbirth activities. Credit: NASA, ESA, and the Hubble Heritage Project (STScI/AURA) Acknowledgment: M. Livio (STScI) and N. Smith (University of California, Berkeley)
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What can we say? Another Hubble stunner, and just wait until you see flythough video below. This is an absolutely gorgeous look inside the Carina Nebula. The radiation from massive stars inside the nebula eats away at cold molecular clouds, creating bizarre, fantasy-like structures. These are one-light-year-tall pillars of cold hydrogen and dust, imaged by the Hubble Space Telescope’s Advanced Camera for Surveys, in a composite image from observations taken in 2005 in hydrogen light (light emitted by hydrogen atoms) along with observations taken in oxygen light (light emitted by oxygen atoms) in 2010. What Hubble can see from about 7,500 light-years away is nothing short of breathtaking.
Here’s the regular video – in which there are 3-D-type flythough effects:
This is an artist's concept of a craggy piece of Solar System debris that belongs to a class of bodies called trans-Neptunian objects (TNOs).Credit: NASA, ESA, and G. Bacon (STScI)
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Out beyond the orbit of Neptune lurk millions of icy bodies called Trans-Neptunian Objects. We haven’t found and seen them them all yet, but astronomers have theorized the numbers. However, since 1992, nearly a thousand TNOs have been observed. Most of them are very small and receive little sunlight, which makes them faint and difficult to spot. But a group of astronomers have devised a clever new technique to find TNOs and discovered 14 just by using archived data from the Hubble Space Telescope, and they hope to be able to uncover hundreds more.
“Trans-Neptunian objects interest us because they are building blocks left over from the formation of the solar system,” said lead author Cesar Fuentes.
As TNOs slowly orbit the sun, they move against the starry background, appearing as streaks of light in time exposure photographs. The team developed software to analyze hundreds of Hubble images hunting for such streaks. After promising candidates were flagged, the images were visually examined to confirm or refute each discovery.
Most TNOs are located near the ecliptic — a line in the sky marking the plane of the solar system (since the solar system formed from a disk of material). Therefore, the team searched within 5 degrees of the ecliptic to increase their chance of success.
The 14 objects include one binary system, kind of like a mini Pluto-Charon system. All were very faint, with most measuring magnitude 25-27 (more than 100 million times fainter than objects visible to the unaided eye).
Additionally, by measuring their motion across the sky, astronomers were able to calculate the orbit and distance for each object. Combining the distance and brightness (plus an assumed albedo or reflectivity), they then estimated the size. The newfound TNOs range from 25 to 60 miles (40-100 km) across.
Unlike planets, which tend to have very flat orbits (known as low inclination), some TNOs have orbits significantly tilted from the ecliptic (high inclination). The team examined the size distribution of TNOs with low- versus high-inclination orbits to gain clues about how the population has evolved over the past 4.5 billion years.
Generally, smaller trans-Neptunian objects are the shattered remains of bigger TNOs. Over billions of years, these objects smack together, grinding each other down. The team found that the size distribution of TNOs with low- versus high-inclination orbits is about the same as objects get fainter and smaller. Therefore, both populations (low and high inclination) have similar collisional histories.
This initial study examined only one-third of a square degree of the sky, meaning that there is much more area to survey. Hundreds of additional TNOs may be hiding in the Hubble archives at higher ecliptic latitudes. Fuentes and his colleagues intend to continue their search.
“We have proven our ability to detect and characterize TNOs even with data intended for completely different purposes,” Fuentes said.
This research has been accepted for publication in The Astrophysical Journal.
An Extraordinary Celestial Spiral. Credit: ESA/NASA & R. Sahai
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The Hubble Space Telescope’s Advanced Camera for Surveys has captured a remarkable image of a spiral in space. No, not a spiral galaxy, (and not another Norway Spiral!) but the formation of an unusual pre-planetary nebula in one of the most perfect geometrical spirals ever seen. The nebula, called IRAS 23166+1655, is forming around the star LL Pegasi (also known as AFGL 3068) in the constellation of Pegasus.
The image shows what appears to be a thin spiral pattern of amazing precision winding around the star, which is itself hidden behind thick dust. Mark Morris from UCLA and an international team of astronomers say that material forming the spiral is moving outwards at a speed of about 50,000 km/hour and by combining this speed with the distance between layers, they calculate that the shells are each separated by about 800 years.
The spiral pattern suggests a regular periodic origin for the nebula’s shape, and astronomers believe that shape is forming because LL Pegasi is a binary star system. One star is losing material as it and the companion star are orbiting each other. The spacing between layers in the spiral is expected to directly reflect the orbital period of the binary, which is estimated to be also about 800 years.
A progression of quasi-concentric shells has been observed around a number of preplanetary nebulae, but this almost perfect spiral shape is unique.
Morris and his team say that the structure of the AFGL 3068 envelope raises the possibility that binary companions are responsible for quasi-concentric shells in most or all of the systems in which they have been observed, and the lack of symmetry in the shells seen elsewhere can perhaps be attributed to orbital eccentricity, to different projections of the orbital planes, and to unfavorable illumination geometries.
Additionally – and remarkably — this object may be illuminated by galactic light.
This image appears like something from the famous “Starry Night” painting by Vincent van Gogh, and reveals what can occur with stars that have masses about half that of the Sun up to about eight times that of the Sun. They do not explode as supernovae at the ends of their lives, but instead can create these striking and intricate features as their outer layers of gas are shed and drift into space. This object is just starting this process and the central star has yet to emerge from the cocoon of enveloping dust.
Supernova 1987A and a glowing gas ring encircling the supernova remnant known as the "String of Pearls." Credit: NASA
The recently refurbished Hubble Space Telescope has taken a new look at Supernova 1987A and its famous “String of Pearls,” a glowing ring 6 trillion miles in diameter encircling the supernova remnant. The sharper and clearer images are allowing astronomers to see the “innards” of the star being ejected into space following the explosion, and comparing the new images with ones taken previously provides a unique glimpse of a young supernova remnant as it evolves. They found significant brightening of the object over time, and also evident is how the shock wave from the star’s explosion has expanded and rebounded.
Kevin France from the University of Colorado Boulder and colleagues compared the new Hubble data on the SN1987A taken in 2010 with older images, and observed the supernova in optical, ultraviolet and near-infrared light. They were able to look at the interplay between the stellar explosion and the ‘String of Pearls’ that encircles the supernova remnant. The gas ring — energized by X-rays — likely was spewed out about 20,000 years before the supernova exploded, and shock waves rushing out from the remnant have been brightening some 30 to 40 pearl-like “hot spots” in the ring — objects that likely will grow and merge together in the coming years to form a continuous, glowing circle.
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“The new observations allow us to accurately measure the velocity and composition of the ejected ‘star guts,’ which tell us about the deposition of energy and heavy elements into the host galaxy,” said France, lead author of the study which was published in Science. “The new observations not only tell us what elements are being recycled into the Large Magellanic Cloud, but how it changes its environment on human time scales.”
The significant brightening that was detected is consistent with some theoretical predictions about how supernovae interact with the galactic environment surrounding them. Discovered in 1987, Supernova 1987A is the closest exploding star to Earth to be detected since 1604 and is located in the nearby Large Magellanic Cloud, a dwarf galaxy adjacent to our own Milky Way Galaxy.
In addition to ejecting massive amounts of hydrogen, 1987A has spewed helium, oxygen, nitrogen and rarer heavy elements like sulfur, silicon and iron. Supernovae are responsible for a large fraction of biologically important elements, including oxygen, carbon and iron found in plants and animals on Earth today, France said. The iron in a person’s blood, for example, is believed to have been made by supernovae explosions.
The team compared STIS observations in January 2010 with Hubble observations made over the past 15 years on 1987A’s evolution. STIS has provided the team with detailed images of the exploding star, as well as spectrographic data — essentially wavelengths of light broken down into colors like a prism that produce unique fingerprints of gaseous matter. The results revealed temperatures, chemical composition, density and motion of 1987A and its surrounding environment, said France.
Since the supernova is roughly 163,000 light-years away, the explosion occurred in roughly 161,000 B.C., said France. One light year is about 6 trillion miles.
“To see a supernova go off in our backyard and to watch its evolution and interactions with the environment in human time scales is unprecedented,” he said. “The massive stars that produce explosions like Supernova 1987A are like rock stars — they live fast, flashy lives and die young.”
France said the energy input from supernovae regulates the physical state and the long-term evolution of galaxies like the Milky Way. Many astronomers believe a supernova explosion near our forming sun some 4 to 5 billion years ago is responsible for a significant fraction of radioactive elements in our solar system today, he said.
“In the big picture, we are seeing the effect a supernova can have in the surrounding galaxy, including how the energy deposited by these stellar explosions changes the dynamics and chemistry of the environment,” said France. “We can use this new data to understand how supernova processes regulate the evolution of galaxies.”
France and his team will be looking at Supernova 1987A again with Hubble’s Cosmic Origins Spectrograph, an instrument which scientists hope will help them better understand the “cosmic web” of of material permeating the cosmos and learn more about the conditions and evolution of the early universe.
The Hubble Space Telescope image of the inner regions of the lensing cluster Abell 1689 that is 2.2 billion light?years away. Light from distant background galaxies is bent by the concentrated dark matter in the cluster (shown in the blue overlay) to produce the plethora of arcs and arclets that were in turn used to constrain dark energy. Image courtesy of NASA?ESA, Jullo (JPL), Natarajan (Yale), Kneib (LAM)
Understanding something we can’t see has been a problem that astronomers have overcome in the past. Now, a group of scientists believe a new technique will meet the challenge of helping to solve one of the biggest mysteries in cosmology today: understanding the nature of dark energy. Using the strong gravitational lensing method — where a massive galaxy cluster acts as a cosmic magnifying lens — an international team of astronomers have been able to study elusive dark energy for the first time. The team reports that when combined with existing techniques, their results significantly improve current measurements of the mass and energy content of the universe.
Using data taken by the Hubble Space Telescope as well as ground-based telescopes, the team analyzed images of 34 extremely distant galaxies situated behind Abell 1689, one of the biggest and most massive known galaxy clusters in the universe.
Through the gravitational lens of Abell 1689, the astronomers, led by Eric Jullo from JPL and Priyamvada Natarajan from Yale University, were able to detect the faint, distant background galaxies—whose light was bent and projected by the cluster’s massive gravitational pull—in a similar way that the lens of a magnifying lens distorts an object’s image.
Using this method, they were able to reduce the overall error in its equation-of-state parameter by 30 percent, when combined with other methods.
The way in which the images were distorted gave the astronomers clues as to the geometry of the space that lies between the Earth, the cluster and the distant galaxies. “The content, geometry and fate of the universe are linked, so if you can constrain two of those things, you learn something about the third,” Natarajan said.
The team was able to narrow the range of current estimates about dark energy’s effect on the universe, denoted by the value w, by 30 percent. The team combined their new technique with other methods, including using supernovae, X-ray galaxy clusters and data from the Wilkinson Microwave Anisotropy Probe (WMAP) spacecraft, to constrain the value for w.
“Dark energy is characterized by the relationship between its pressure and its density: this is known as its equation of state,” said Jullo. “Our goal was to try to quantify this relationship. It teaches us about the properties of dark energy and how it has affected the development of the Universe.”
Dark energy makes up about 72 percent of all the mass and energy in the universe and will ultimately determine its fate. The new results confirm previous findings that the nature of dark energy likely corresponds to a flat universe. In this scenario, the expansion of the universe will continue to accelerate and the universe will expand forever.
The astronomers say the real strength of this new result is that it devises a totally new way to extract information about the elusive dark energy, and it offers great promise for future applications.
According to the scientists, their method required multiple, meticulous steps to develop. They spent several years developing specialized mathematical models and precise maps of the matter — both dark and “normal” — that together constitute the Abell 1689 cluster.
The findings appear in the August 20 issue of the journal Science.
Astronomers have found unexpected rings and arcs of ultraviolet light around a selection of galaxies, four of which are shown here as viewed by NASA's and the European Space Agency's Hubble Space Telescope. Image credit: NASA/ESA /JPL-Caltech/STScI/UCLA
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Title this ‘Zombie Galaxies’ or ‘Night of the Living Galaxies.’ Astronomers have found mysterious, giant loops of ultraviolet light around old, massive galaxies, which were presumed to be “dead,” and these galaxies seem to have come back to life. Somehow these “over-the-hill galaxies” have been infused with fresh gas to form new stars that power these truly gargantuan rings, some of which could encircle several Milky Way galaxies.
The discovery of these rings implies that old bloated galaxies that were once devoid of star-making can be reignited with star birth, and that galaxy evolution does not proceed straight from the cradle to the grave.
“In a galaxy’s lifetime, it must make the transition from an active, star-forming galaxy to a quiescent galaxy that does not form stars,” said Samir Salim, lead author of a recent study and a research scientist in the department of astronomy at Indiana University, Bloomington. “But it is possible this process goes the other way, too, and that old galaxies can be rejuvenated.”
Using two orbiting observatories, NASA’s Galaxy Evolution Explorer and Hubble Space Telescope, the astronomers surveyed a vast region of the sky in ultraviolet light. GALEX picked out 30 elliptical and lens-shaped “early” galaxies with puzzlingly strong ultraviolet emissions but no signs of visible star formation, and Hubble was used to take a closer look.
What Hubble showed shocked the astronomers. Three-quarters of the galaxies were spanned by great, shining rings of ultraviolet light, with some ripples stretching 250,000 light-years. A few galaxies even had spiral-shaped ultraviolet features.
“We haven’t seen anything quite like these rings before,” said Michael Rich, co-author of the paper and a research astronomer at UCLA. “These beautiful and very unusual objects might be telling us something very important about the evolution of galaxies.”
But astronomers are unsure where the gas for this galactic resurrection came from and how it has created rings. One possibility is that a smaller galaxy merged with a big, old one, bringing in fresh gas to spawn hordes of new stars, and could in rare instances give rise to the ring structures as well.
But the researchers have their doubts about this origin scenario. “To create a density shock wave that forms rings like those we’ve seen, a small galaxy has to hit a larger galaxy pretty much straight in the center,” said Salim. “You have to have a dead-on collision, and that’s very uncommon.”
Another option that the astronomers like better is that the rejuvenating spark could have come from a gradual sopping-up of the gas in the so-called intergalactic medium, the thin soup of material between galaxies. This external gas could generate these rings, especially in the presence of bar-like structures that span some galaxies’ centers.
Ultimately, more observations will be needed to show how these galaxies began growing younger and lit up with humongous halos. Salim and Rich plan to search for more evidence of bars, as well as faint structures that might be the remnants of stellar blooms that occurred in the galaxies’ pasts. Rather like recurring seasons, it may be that galaxies stirred from winter can breed stars again and then bask in another vibrant, ultraviolet-soaked summer.
The study detailing the findings appeared in the April 21 issue of the Astrophysical Journal.
