TWO VIEWS OF CERES

FROM:  NASA 

These two views of Ceres were acquired by NASA's Dawn spacecraft on Feb. 12, 2015, from a distance of about 52,000 miles (83,000 kilometers) as the dwarf planet rotated. The images have been magnified from their original size. The Dawn spacecraft is due to arrive at Ceres on March 6, 2015. Dawn's mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK, Inc., of Dulles, Virginia, designed and built the spacecraft. JPL is managed for NASA by the California Institute of Technology in Pasadena. The framing cameras were provided by the Max Planck Institute for Solar System Research, Göttingen, Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The visible and infrared mapping spectrometer was provided by the Italian Space Agency and the Italian National Institute for Astrophysics, built by Selex ES, and is managed and operated by the Italian Institute for Space Astrophysics and Planetology, Rome. The gamma ray and neutron detector was built by Los Alamos National Laboratory, New Mexico, and is operated by the Planetary Science Institute, Tucson, Arizona. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

THE FUNDAMENTAL PHYSICIST INVESTIGATES THE UNIVERSE

FROM:  NATIONAL SCIENCE FOUNDATION 
Scientist who helped discover the expansion of the universe is accelerating
Breakthrough Prize winner continues investigating fundamental physics of the world
February 3, 2015

In the late 1980s, astrophysicist Saul Perlmutter and his colleagues set out to determine how much the expansion of the universe was slowing. At the time, the prevailing belief among scientists was that gravity would be slowing the expansion, perhaps enough to ultimately switch to a contracting universe that would cause the galaxies to draw even closer together.

Of course, the world learned in 1998 that this was not the case. As it turned out, the expansion of the universe was, in fact, not slowing at all, but speeding up.

"That means there is something else going on besides gravity," says Perlmutter, director of the Supernova Cosmology Project at Lawrence Berkeley National Laboratory, who shared the 2011 Nobel Prize in physics for the work. "We thought we understood the physics, but this was a real surprise."

The "something else" is an enduring mystery that continues to fascinate, and elude, scientists today, Perlmutter among them. Astrophysicists refer to it as "dark energy."

"We call it 'dark' because we don't know what it is," he says. "But it possibly means that as much as 70 percent of the universe could be made out of this previously unknown energy."

Moreover, researchers don't know why the universe is speeding up. "But it leaves the possibility that if whatever is speeding it up goes away, then it will start to slow down again," he says. "There is still a lot in play, and we are still trying to learn what it is."

It's an exciting prospect, since research into the ongoing puzzle of dark energy could provide "a new understanding of the fundamental physics of the world," Perlmutter says. "We have no idea what the consequences will be if we learn what dark energy is. But history has shown us that these kinds of steps forward in our fundamental understanding make us a more capable civilization.

"Moreover, learning how this world is put together, in a way, is a deep, almost poetic experience," he adds.

Perlmutter, also a professor of physics at the University of California, Berkeley, is a recent recipient of the 2015 Breakthrough Prize in Fundamental Physics, sharing the $3 million award with his Supernova Cosmology Project team, and with Brian P. Schmidt, an astrophysicist at the Australian National University Mount Stromlo Observatory and Research School, and Adam Riess, an astrophysicist at The Johns Hopkins University and the Space Telescope Science Institute, and the High-Z Supernova Search team that they led.

The three, who also shared the 2011 Nobel, received the Breakthrough Prize together with their teams for their work providing evidence that the expansion of the universe is accelerating.

For Perlmutter, the research leading to this discovery began in 1987, with a project under the auspices of the newly created Center for Particle Astrophysics, a National Science Foundation science and technology center based at Berkeley. Perlmutter, a postdoctoral fellow at the time, designed the study with Carl Pennypacker, also a researcher in the group which was then under the direction of physics professor Richard Muller, a 1978 NSF Alan T. Waterman award winner.

"When the project began in 1987, the standard picture of cosmology was that the universe was expanding, but everyone assumed it would slow down because gravity would attract everything to everything else," Perlmutter says. "We wanted to find out: How dense is the universe? How much is it slowing down?"

The scientists decided to try to measure the state of the universe by looking several billion years in the past using a new understanding in the field about a specific type of supernova, or exploding star, called Type Ia, that explodes in a similar way every time. "Since they brighten to essentially the same brightness every time, and then fade away, we can tell how far away they are by measuring how bright they appear to us," he says.

Since light always travels at 186,000 miles per second, researchers can then use the distance measurement to calculate how long ago these supernovae exploded. Also, while the light is traveling--and the universe is expanding--the light waves traveling from the exploding supernova stretch along with everything else. As these wavelengths stretch, they look redder and redder, a phenomenon in astronomy known as "redshift."

"When the supernova explodes, it sends out mostly blue light," Perlmutter explains. "That blue light means a short wave length of light. The more it stretches, the more it starts to turn red. And that tells us the amount the universe stretched between the time of the explosion, and today."

Taken together, the brightness and colors of the supernovae provide compelling evidence of an accelerating expanding universe. The degree of their brightness reveals how far back in time the star exploded, and the extent of redshift indicates how much the universe has expanded during that time. So a series of measurements each taken for a supernova exploding at a different time throughout history--7, 4 and 2 billion years ago--revealed that the stretching of the universe was increasing, and that it wasn't slowing down at all.

The difficulty initially was finding these supernovae in time, since they are rare and random, and reserving a stint at some of the largest and most advanced telescopes in the world, not to mention hoping for good weather.

Ultimately, they found a way to make discovering Type Ia supernovae more predictable.

"Instead of watching one galaxy, we figured out how to use novel wide-field cameras on the big telescopes to watch thousands of galaxies," he says. "You take a bunch of images one night, then go away, then come back two and half weeks later and take another bunch of images. Now you have two almost identical images of the galaxies, but with a time gap just long enough to allow a new supernova to appear."

"Everything had to happen like clockwork, and anytime the night was cloudy, you'd have to scramble to cover that time another night someplace else," he says.

The researchers developed a special computer program "to hunt through thousands of specks of light to find a new speck that wasn't there before," that is, looking for a new supernova. Then, using a spectrograph, they analyzed the light waves to determine whether the supernova was a Type Ia, the type they needed to study. Finally, they ran a series of observations following the supernova, obtaining images four to six more times as it brightened, then faded, which told them how bright it was at its peak.

"When we started the project, I thought we were just going out and doing a simple measurement of the brightness of exploding stars, and finding out whether the universe was going to end," he says. "It turned out that what we discovered was a huge surprise. We have been comparing it to throwing an apple up in the air, and finding that it doesn't fall back to earth, but instead blasts off into outer space, mysteriously moving faster and faster."

-- Marlene Cimons, National Science Foundation
Investigators
Saul Perlmutter
Related Institutions/Organizations
University of California-Berkeley

NASA VIDEO | SWIFT: A DECADE OF GAME-CHANGING ASTROPHYSICS

NSF SUPPORTS DIVERSITY WITH ASTRONOMY PROGRAM

FROM:  NATIONAL SCIENCE FOUNDATION 

Making stars

Astronomy program provides tools, support to enhance diversity

October 7, 2014

Like so many other children, Fabienne Bastien did not like to go to sleep at bedtime.

She recalls her mother lying alongside her, telling her to look out her window into the night sky because her guardian angel was there. And as she searched for this elusive guardian angel, what she found instead was the moon and stars, among other astronomical delights.

Despite Washington, D.C., metro-area light pollution that can restrict one's view of the cosmos, Bastien pinpoints that moment as the one when she got hooked on astronomy, knowing it held her future, if not an actual guardian angel.

Many astronomers and astrophysicists speak of that same source of inspiration. But, while our solar system's immensity and beauty have an almost universal appeal, the astronomy and astrophysics career field has had very little representation from minority populations.

In a study done by the American Astronomical Society, which includes most professionals and many students in these fields, only 21 percent of its members is female, which is light-years ahead of the representation of African Americans and Hispanics/Latinos--1 percent and 3 percent, respectively.

Not surprisingly, those numbers have prompted a call for diversity within the astro community.

In 2008, the National Science Foundation (NSF) started a program called Partnerships in Astronomy and Astrophysics Research and Education (PAARE, pronounced "pair"). Its goal was to identify and explore ways to repair "leaks" in the astronomy/astrophysics career pipeline for minority students. In many cases, minority students would start out studying astronomy, but they weren't making it all the way through the pipeline to pursue science careers.

When Bastien finished her undergraduate degree at the University of Maryland, she too wasn't sure whether she was appropriately prepared for the rigors of a grad school education in astronomy.

"I was petrified of grad school," she said. "I hadn't taken advantage of research opportunities as an undergrad largely due to personal challenges. But also because our department was so big, I fell between the cracks there."

PAARE aimed to make the face of astronomy more inclusive by seeing that minority students like Bastien got the right mix of resources, mentoring and encouragement. The partnership found that this required a multi-faceted approach that could target those pipeline points where "leaks" were most likely and "pair" some strong astronomy programs with schools that have more diverse populations, providing mentoring and support.

In Bastien's case, the PAARE Fisk-Vanderbilt Masters-to-Ph.D. Bridge Program proved to be one where she not only got her Ph.D., but had the opportunity to analyze stellar variability data, which led to a paper in Nature, being named a Hubble fellow and to her current postdoctoral work at Penn State.

The leaky pipeline

"We currently fund several highly complementary PAARE partnerships, which attack the leaky pipeline at different stages," said Dan Evans, the NSF program director who manages PAARE funding for the Division of Astronomical Sciences. "We're deeply concerned about the underrepresentation of minority students in astronomy and are massively proud of the successes of the students and staff who have participated in PAARE. We are exposing students to cutting-edge research. We are providing important new opportunities. And mentoring is utterly critical."

Though the partnerships target different points in the pipeline, they all emphasize mentoring, access to research opportunities and resources early on. They also emphasize an infrastructure that can address both academic and personal issues that might hinder progress.

"Queens is the most diverse county in the country," said Tim Paglione, director of AstroCom NYC, a partnership between astronomers at the City Universities of New York (CUNY), the American Museum of Natural History and Columbia University. Of the current PAARE partnerships, this is the only one that focuses exclusively on undergraduate students, targeting freshmen and sophomores. It also has the added challenge of CUNY being located throughout New York City, creating unique transportation issues that can deter students who feel inadequately prepared or supported.

That's why this program only accepts four new students each year. It supports students with summer fellowships, school scholarships, transportation stipends and program-provided laptops. It also provides long-term career mentors, research mentors, travel to observatories and professional meetings and membership in the American Astronomical Society.

"The problem is gigantic, but our astronomy field is also small," Paglione said. "That means even with our little program, we can have an impact. If we graduated two students each year from underrepresented groups who then went onto graduate school, we would be one of the leading programs in the country."

Keivan Stassun started a PAARE-like partnership even before PAARE existed, using funding from his NSF CAREER award in 2003 to develop the Fisk-Vanderbilt program, which focused on the potential pipeline leak at this juncture.

"That CAREER award gave me seed funding to do things like develop a website and recruit a couple of students as research assistants," Stassun said. "The CAREER grant got the whole thing going, both in terms of cash and caché as I got buy-in from both universities."

Broader than just astronomy, Stassun' s program has admitted 78 students in physics, biology, chemistry, materials science and astronomy, with the belief that they can impact these STEM disciplines as well. "This felt like the perfect program for me," Bastien recalled. "The extra encouragement helped. I was immediately working on real science--on rare eruptive young stars--because they serendipitously had these data they needed analyzed."

Another potential leak in this pipeline comes right after college, and South Carolina State University (SCSU) partnered with the NSF-funded National Optical Astronomy Observatory and Clemson University to address the loss of minority astronomy students at this stage of their education.

"We hoped to mirror Keivan's success at Vanderbilt," said Don Walter, who started the Partnership in Observational and Computational Astronomy, based on an undergraduate physics curriculum at SCSU. "We overestimated the number of students we'd get involved, so we haven't yet seen the numbers at the grad program that we hoped for, but the momentum is there, and we believe we have the right supports in place."

The SCSU partnership admittedly has had different obstacles and issues. It doesn't have full-time researchers because SCSU is a predominantly undergraduate school. The astrophysics portion of the curriculum is a concentration, not a degree. And the STEM graduate programs are a few hours away at Clemson, not nearby.

Mentoring makes the difference

"We try to spend a lot of time with our students as soon as possible. Because they don't take their first physics courses until their second year, it would be easy for them to get lost," Walter said. "I'll ask them to come by to make sure we connect early on--even waiting outside their classrooms if my emails don't bring them in. Students need early interaction."

This is a common theme throughout PAARE partnerships. Interaction with other students at the same and more advanced levels, as well as faculty, seems critical to success.

"We've added a number of mentoring layers," Stassun said about the Fisk-Vanderbilt program. "We assign to all incoming students a pair of peer mentors known as 'bridge buddies' who are students just one year ahead, and another mentor who is a few years further ahead. That way, they can see their future in front of them. We now also have a postdocs association, where the postdocs spend three-quarters of their time on their own research, but also a quarter of their time mentoring. They hold office hours, so students can talk to them, which offers a different perspective from faculty advisers."

At SCSU, one of the biggest challenges actually has been personal and financial problems that interfere with students staying in school.

"Some good students have had major personal or family issues," he said. "Money is tight, and many students find it too difficult to balance school life with demands in their personal lives. One female student in our physics program was an A-B student, but in the middle of the semester, her parents asked her to return home to care for a sick brother. She would have been a good undergraduate student and good graduate student."

Success determined by grit?

Interestingly enough, the admissions process for these PAARE partnerships has gone beyond evaluating just grades and test scores.

Stassun referred to a Nature article that he published this year with colleague Casey Miller about the Graduate Record Examination, or GRE, gender and ethnic bias that was discovered using published data from the Educational Testing Service that makes those tests. Their study found that women score approximately 80 points lower than men on the test's math section; and African Americans, approximately 200 points lower than Whites and Asians, on average.

For that reason, Stassun and his team put together a different set of metrics to measure something he refers to as "grit" or performance character.

"We found that the most successful students weren't necessarily the ones with the highest test scores," he said. "Graduate school is about persistence, so it makes sense to try and determine a candidate's capacity for being persistent. Consequently, we have achieved a very large, diverse program with a 90-percent Ph.D. persistence rate versus the national rate which is barely better than 50 percent." In other words, 90 percent of the students at Fisk-Vanderbilt are getting their doctoral degrees. He credits that success to careful, yet diverse selection and smart mentoring.

"PAARE funding makes a difference," Walter said. "In the August American Institute of Physics newsletter, SCSU was tied for eighth position nationally in terms of African American physics bachelors of science degree graduates during the five-year period, 2008-2012. We'd only graduated 12, but because the pool is so small, we're one of the top schools. PAARE helped us provide our students with meaningful internships at places like the National Optical Astronomy Observatory, which keeps their interest alive while giving them important experience."

Ariel Diaz, who attends the CUNY program, is a PAARE student who has benefitted from those experiences and demonstrated his "grit." A former Marine, he lives in New York City with his ailing father, whom he cares for. His astronomy interest was piqued in an introductory class that was far from the "easy A" he thought it would be. However, he found he really enjoyed the class, and Paglione's team recognized a student who had the wherewithal to succeed. Today, Diaz sifts through X-ray data from Chandra Observatory, looking for signals that could indicate black holes or other astronomical events.

"He's grown as a student. He's building a vision of himself in this career," Paglione said. "And honestly, that's what we want to do here. We want our students to see that future in themselves."

-- Ivy F. Kupec
Investigators
Donald Walter
Keivan Stassun
Timothy Paglione
Related Institutions/Organizations
Fisk University
CUNY York College
University of Texas at El Paso
South Carolina State University

NSF-FUNDED SCIENTIST LOOKS AT WHY GALAXIES CHANGE

FROM:  NATIONAL SCIENCE FOUNDATION 

Exploring dramatic changes in galaxies

Scientist hopes to uncover physical process behind the changes, including cosmic webs and supermassive black holes

The evolution of galaxies over billions of years offers any number of tantalizing clues about the origins of the universe. Alison Coil is trying to solve some of these mysteries by studying how galaxies have been changing over time, and why.

"Galaxies have changed dramatically," says Coil, an associate professor of physics at the University of California, San Diego. "In the past, for example, they formed more stars, and had smaller supermassive black holes. These black holes were more active, brighter and gobbling up materials faster."

The National Science Foundation (NSF)-funded scientist is conducting three research projects with the goal of uncovering some of the physical processes underlying these dramatic changes.

"We are looking at large statistical samples of what galaxies are doing, including nearby galaxies and distant ones," she says.

These include looking at the stellar mass of both nearby and distant galaxies, comparing the properties of galaxies that still are forming stars with those that are not; studying the "clustering" behavior of distant galaxies, that is, the process by which they form a "cosmic web," a filamentary-like structure that resembles a sponge; and quantifying supermassive black holes among distant galaxies.

"This may help us discover if we live in a typical kind of galaxy, and how we came to be, and why we're here," she says. "It tells us something about where we came from. I'd like to understand the galaxy population as a whole, as it helps to put our own Milky Way into context."

Coil is conducting her research under an NSF Faculty Early Career Development (CAREER) award, which she received in 2011. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education, and the integration of education and research within the context of the mission of their organization.

One project is looking halfway back to the Big Bang to compare galaxies still forming stars with those that have stopped. These include nearby galaxies, which formed later and are brighter, as well as distant galaxies, which developed when the universe was younger, and are faint.

"Within the population that is no longer forming stars, there's a lot of growth happening for the lower mass galaxies, they are still getting bigger and there is more of them," she says. "For the population still forming stars, the massive galaxies disappear, and are turning into the other population, those whose star formation has turned off.

"We don't know why," she adds. "We know that one kind turns into the other kind, but we don't know what is shutting off star formation."

Her team also is examining distant galaxies and how they form "cosmic webs," which are clusters of galaxies grouped together like foam, likely the result of gravitational pull.

"The thing that is interesting here is that if you look at the clustering in galaxies still forming stars, and those not forming stars, the clustering is different," she says.

Those galaxies no longer producing stars are more clustered together, and typically are located in the middle of the web, she says.

"Those that are still forming stars tend to be on the outskirts," she says. "We are trying to understand this, whether this has to do with when the galaxies are formed, how much mass they have and whether being near other galaxies shuts off star formation."

Finally, she and her colleagues also are studying supermassive black holes located in the centers of distant galaxies, trying to quantify them.

"We want to know how many galaxies have these super massive black holes, which seem to be fairly common," she says. "They have to be shining for us to see them, and they shine when they are accreting material, that is, when stars and gas fall into the black hole. When you see this light, you know there is a black hole actively accreting. But there are other black holes that exist that we can't see. We want to know why some are shining--accreting--and some aren't."

Much of her work uses data generated by the PRIsm Multi-object Survey (PRIMUS), the largest faint galaxy spectroscopic redshift (which refers to a shift in the spectra of very distant galaxies toward longer wavelengths, usually considered evidence that the universe is expanding) survey taken to date.

As part of the grant's educational component, Coil created and taught a new course during the fall 2013 semester on stars and black holes, and convinced her department to split a pre-existing course entitled "the universe" into two courses, including "stars and black holes," and "galaxies and cosmology."

"The new course is much more fun to teach, as we can spend more time on concepts and class discussions," she says. "I found that the students learned more, at a deeper level. I am very pleased with the new course and hope to attract more students to the lower division astrophysics survey courses as a result."

She also is developing a proposal to add an astrophysics doctoral track in her department, which currently has a physics and a biophysics track. "The astrophysics PhD track would allow students to take more graduate level courses in astrophysics and begin astrophysics research in their first year, a year earlier than the physics PhD track," she says. "I hope to recruit more astrophysics graduate students to UCSD as a result of the new track."

She also informally mentors several female undergraduate and graduate students in the department through individual meetings, and holds monthly meetings of the "women in physics" group she established for women graduate students and postdocs.

During the last year, among other things, the group sponsored two guest speakers--a female faculty in another department and a colloquium speaker who works in science policy--and discussed such topics as diversity in faculty hiring, maternity leave policies, and unconscious bias.

She also runs a one-day physics outreach program for the Reach for Tomorrow foundation, which targets underprivileged middle school youth. About 50 students are participating this year.

Finally, every June she leads a similar program with the Tech Trek program, which is aimed at middle school girls interested in math and science. About 25 girls participate in the physics portion of the program, which involves hands-on demonstrations, and a soldering lab, all run by graduate students and postdocs in the department.

"I specifically recruit mostly women students and postdocs to help run the event, so that the girls can meet and interact with many women who were actively pursuing physics careers," she says.

-- Marlene Cimons, National Science Foundation
Investigators
Alison Coil
Related Institutions/Organizations
University of California-San Diego

500 YEARS TO EARTH: PLANET FOUND IN THE 'HABITABLE ZONE'

FROM:  NASA 

Kepler-186f resides in the Kepler-186 system about 500 light-years from Earth in the constellation Cygnus. The system is also home to four inner planets, seen lined up in orbit around a host star that is half the size and mass of the sun.
Image Credit: NASA Ames-SETI Institute-JPL-Caltech

Using NASA's Kepler Space Telescope, astronomers have discovered the first Earth-size planet orbiting a star in the "habitable zone" -- the range of distance from a star where liquid water might pool on the surface of an orbiting planet. The discovery of Kepler-186f confirms that planets the size of Earth exist in the habitable zone of stars other than our sun.

While planets have previously been found in the habitable zone, they are all at least 40 percent larger in size than Earth and understanding their makeup is challenging. Kepler-186f is more reminiscent of Earth.

"The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth," said Paul Hertz, NASA's Astrophysics Division director at the agency's headquarters in Washington. "Future NASA missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind's quest to find truly Earth-like worlds."
Although the size of Kepler-186f is known, its mass and composition are not. Previous research, however, suggests that a planet the size of Kepler-186f is likely to be rocky.

"We know of just one planet where life exists -- Earth. When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth," said Elisa Quintana, research scientist at the SETI Institute at NASA's Ames Research Center in Moffett Field, Calif., and lead author of the paper published today in the journal Science. "Finding a habitable zone planet comparable to Earth in size is a major step forward."

Kepler-186f resides in the Kepler-186 system, about 500 light-years from Earth in the constellation Cygnus. The system is also home to four companion planets, which orbit a star half the size and mass of our sun. The star is classified as an M dwarf, or red dwarf, a class of stars that makes up 70 percent of the stars in the Milky Way galaxy.

"M dwarfs are the most numerous stars," said Quintana. "The first signs of other life in the galaxy may well come from planets orbiting an M dwarf."
Kepler-186f orbits its star once every 130-days and receives one-third the energy from its star that Earth gets from the sun, placing it nearer the outer edge of the habitable zone. On the surface of Kepler-186f, the brightness of its star at high noon is only as bright as our sun appears to us about an hour before sunset.
"Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has," said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames, and co-author of the paper. "Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth."

The four companion planets, Kepler-186b, Kepler-186c, Kepler-186d, and Kepler-186e, whiz around their sun every four, seven, 13, and 22 days, respectively, making them too hot for life as we know it. These four inner planets all measure less than 1.5 times the size of Earth.

The next steps in the search for distant life include looking for true Earth-twins -- Earth-size planets orbiting within the habitable zone of a sun-like star -- and measuring the their chemical compositions. The Kepler Space Telescope, which simultaneously and continuously measured the brightness of more than 150,000 stars, is NASA's first mission capable of detecting Earth-size planets around stars like our sun.

Ames is responsible for Kepler's ground system development, mission operations, and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes Kepler science data. Kepler is NASA's 10th Discovery Mission and was funded by the agency's Science Mission Directorate.

SUPERCOMPUTERS PREDICT SIGNS OF BLACK HOLES CONSUMING STARS

Right:  Black Hole Caught in a Stellar Homicide.  This computer-simulated image shows gas from a star that is ripped apart by tidal forces as it falls into a black hole. Some of the gas also is being ejected at high speeds into space.  Image Credit: NASA, S. Gezari (The Johns Hopkins University), and J. Guillochon (University of California, Santa Cruz).

FROM:  NATIONAL SCIENCE FOUNDATION 

Cosmic slurp

Georgia Tech researchers use supercomputers to understand and predict signs of black holes swallowing stars

April 14, 2014

Somewhere out in the cosmos an ordinary galaxy spins, seemingly at slumber. Then all of a sudden, WHAM! A flash of light explodes from the galaxy's center. A star orbiting too close to the event horizon of the galaxy's central supermassive black hole has been torn apart by the force of gravity, heating up its gas and sending out a beacon to the far reaches of the universe.

In a universe with tens of billions of galaxies, how would we see it? What would such a beacon look like? And how would we distinguish it from other bright, monumental intergalactic events, such as supernovas?

"Black holes by themselves do not emit light," said Tamara Bogdanovic, an assistant professor of physics at the Georgia Institute of Technology. "Our best chance to discover them in distant galaxies is if they interact with the stars and gas that are around them."

In recent decades, with improved telescopes and observational techniques designed to repeatedly survey the vast numbers of galaxies in the sky, scientists noticed that some galaxies that previously looked inactive would suddenly light up at their very center.

"This flare of light was found to have a characteristic behavior as a function of time. It starts very bright and its luminosity then decreases in time in a particular way," she explained. "Astronomers have identified those as galaxies where a central black hole just disrupted and 'ate' a star. It's like a black hole putting up a sign that says 'Here I am.'"

Using a mix of theoretical and computer-based approaches, Bogdanovic tries to predict the dynamics of events such as the black-hole-devouring-star scenario described above, also known as a "tidal disruption." Such events would have a distinct signature to someone analyzing data from a ground-based or space-based observatory.

Using National Science Foundation-funded supercomputers at the Texas Advanced Computing Center (Stampede) and the National Institute for Computational Sciences (Kraken), Bogdanovic and her collaborators recently simulated the dynamics of these super powerful forces and charted their behavior using numerical models.

Tidal disruptions are relatively rare cosmic occurrences. Astrophysicists have calculated that a Milky Way-like galaxy stages the disruption of a star only once in about 10,000 years. The luminous flare of light, on the other hand, can fade away in only a few years. Because it is such a challenge to pinpoint tidal disruptions in the sky, astronomical surveys that monitor vast numbers of galaxies simultaneously are crucial.

Huge difference

So far, only a few dozen of these characteristic flare signatures have been observed and deemed "candidates" for tidal disruptions. But with data from PanSTARRS, Galex, the Palomar Transient Factory and other upcoming astronomical surveys becoming available to scientists, Bogdanovic believes this situation will change dramatically.

"As opposed to a few dozen that have been found over the past 10 years, now imagine hundreds per year--that's a huge difference!" she said. "It means that we will be able to build a varied sample of stars of different types being disrupted by supermassive black holes."

With hundreds of such events to explore, astrophysicists' understanding of black holes and the stars around them would advance by leaps and bounds, helping determine some key aspects of galactic physics.

"A diversity in the type of disrupted stars tells us something about the makeup of the star clusters in the centers of galaxies," Bodganovic said. "It may give us an idea about how many main sequence stars, how many red giants, or white dwarf stars are there on average."

Tidal disruptions also tell us something about the population and properties of supermassive black holes that are doing the disrupting.

"We use these observations as a window of opportunity to learn important things about the black holes and their host galaxies," she continued. "Once the tidal disruption flare dims below some threshold luminosity that can be seen in observations, the window closes for that particular galaxy."

Role of supercomputer

In a recent paper submitted to the Astrophysical Journal, Bogdanovic, working with Roseanne Cheng (Center for Relativistic Astrophysics at Georgia Tech) and Pau Amaro-Seoane (Albert Einstein Institute in Potsdam, Germany), considered the tidal disruption of a red giant star by a supermassive black hole using computer modeling.

The paper comes on the heels of the discovery of a tidal disruption event in which a black hole disrupted a helium-rich stellar core, thought to be a remnant of a red giant star, named PS1-10jh, 2.7 billion light years from Earth.

The sequence of events they described aims to explain some unusual aspects of the observational signatures associated with this event, such as the absence of the hydrogen emission lines from the spectrum of PS1-10jh.

As a follow-up to this theoretical study, the team has been running simulations on Kraken and Stampede, as well as Georgia Tech's Keeneland supercomputer. The simulations reconstruct the chain of events by which a stellar core, similar to the remnant of a tidally disrupted red giant star, might evolve under the gravitational tides of a massive black hole.

"Calculating the messy interplay between hydrodynamics and gravity is feasible on a human timescale only with a supercomputer," Cheng said. "Because we have control over this virtual experiment and can repeat it, fast forward, or rewind as needed, we can examine the tidal disruption process from many perspectives. This in turn allows us to determine and quantify the most important physical processes at play."

The research shows how supercomputer simulations complement and constrain theory and observation.

"There are many situations in astrophysics where we cannot get insight into a sequence of events that played out without simulations. We cannot stand next to the black hole and look at how it accretes gas. So we use simulations to learn about these distant and extreme environments," Bogdanovic said.

One of Bogdanovic's goals is to use the knowledge gained from simulations to decode the signatures of observed tidal disruption events.

"The most recent data on tidal disruption events is already outpacing theoretical understanding and calling for the development of a new generation of models," she explained. "The new, better quality data indicates that there is a great diversity among the tidal disruption candidates. This is contrary to our perception, based on earlier epochs of observation, that they are a relatively uniform class of events. We have yet to understand what causes these differences in observational appearance, and computer simulations are guaranteed to be an important part of this journey."

Investigators
Roseanne Cheng
Pau Amaro-Seoane
Tamara Bogdanovic

AN ALIEN'S LOOK AT OUR SOLAR SYSTEM

FROM: NASA
　

Dust Models Paint Alien's View of Solar System
Dust in the Kuiper Belt, the cold-storage zone that includes Pluto, creates a faint infrared disk potentially visible to alien astronomers looking for planets around the sun. Neptune's gravitational imprint on the dust is detectable in new simulations of how this dust moves through the solar system. The simulations show how the distant view of the solar system might have changed over its history.

ANTARCTIC TELESCOPE SUPPORTS EXPLANATION OF DARK ENERGY FORCE

FROM NATIONAL SCIENCE FOUNDATION
Credit: Daniel Luong-Van, National Science Foundation

NSF-funded 10-meter South Pole Telescope in Antarctica provides new support for the most widely accepted explanation of dark energy, the source of the mysterious force that is responsible for the accelerating expansion of the universe.

April 2, 2012
Analysis of data from the National Science Foundation- (NSF) funded 10-meter South Pole Telescope (SPT) in Antarctica provides new support for the most widely accepted explanation of dark energy, the source of the mysterious force that is responsible for the accelerating expansion of the universe.

The results begin to hone in on the tiny mass of the neutrinos, the most abundant particles in the universe, which until recently were thought to be without mass.
The SPT data strongly support Albert Einstein's cosmological constant--the leading model for dark energy--even though researchers base the analysis on only a fraction of the SPT data collected and only 100 of the over 500 galaxy clusters detected so far.

"With the full SPT data set we will be able to place extremely tight constraints on dark energy and possibly determine the mass of the neutrinos," said Bradford Benson, an NSF-funded postdoctoral scientist at the University of Chicago's Kavli Institute for Cosmological Physics.

Benson presented the SPT collaboration's latest findings, Sunday, April 1, at the American Physical Society meeting in Atlanta.

These most recent SPT findings are only the latest scientifically significant results produced by NSF-funded researchers using the telescope in the five years since it became active, noted Vladimir Papitashvili, Antarctic Astrophysics and Geospace Sciences program director in NSF's Office of Polar Programs.

"The South Pole Telescope has proven to be a crown jewel of astrophysical research carried out by NSF in the Antarctic," he said. "It has produced about two dozen peer-reviewed science publications since the telescope received its 'first light' on Feb. 17, 2007. SPT is a very focused, well-managed and amazing project."

The 280-ton SPT stands 75 feet tall and is the largest astronomical telescope ever built in the clear and dry air of Antarctica. Sited at NSF's Amundsen-Scott South Pole station at the geographic South Pole, it stands at an elevation of 9,300 feet on the polar plateau. Because of its location at the Earth's axis, it can conduct long-term observations.

NSF manages the U.S. Antarctic Program through which it coordinates all U.S. scientific research on the southernmost continent and aboard ships in the Southern Ocean as well as providing the necessary related logistics support.

An international research collaboration led by the University of Chicago manages the South Pole Telescope. The collaboration includes research groups at Argonne National Laboratory; Cardiff University in Wales; Case Western Reserve University; Harvard University; Ludwig-Maximilians-Universität in Germany; the Smithsonian Astrophysical Observatory; McGill University in Canada; the University of California, Berkeley; the University of California, Davis; the University of Colorado Boulder; and the University of Michigan, as well as individual scientists at several other institutions.

SPT specifically was designed to tackle the dark-energy mystery. The 10-meter telescope operates at millimeter wavelengths to make high-resolution images of Cosmic Microwave Background (CMB) radiation, the light left over from the big bang.

Scientists use the CMB to search for distant, massive galaxy clusters that can be used to pinpoint the properties of dark energy and also help define the mass of the neutrino.
"The CMB is literally an image of the universe when it was only 400,000 years old, from a time before the first planets, stars and galaxies formed in the universe," Benson said. "The CMB has travelled across the entire observable universe, for almost 14 billion years, and during its journey is imprinted with information regarding both the content and evolution of the universe."

The new SPT results are based on a new method that combines measurements taken by the telescope and by NASA and European Space Agency X-ray satellites, and extends these measurements to larger distances than previously achieved.

The most widely accepted property of dark energy is that it leads to a pervasive force acting everywhere and at all times in the universe. This force could be the manifestation of Einstein's cosmological constant that assigns energy to space, even when it is free of matter and radiation.

Einstein considered the cosmological constant to be one of his greatest blunders after learning that the universe is not static, but expanding.

In the late 1990s, astronomers discovered the universe's expansion appears to be accelerating according to cosmic distance measurements based on the relatively uniform luminosity of exploding stars. The finding was a surprise because gravity should have been slowing the expansion, which followed the big bang.

Einstein introduced the cosmological constant into his theory of general relativity to accommodate a stationary universe, the dominant idea of his day. But his constant fits nicely into the context of an accelerating universe, now supported by countless astronomical observations.

Others hypothesize that gravity could operate differently on the largest scales of the universe. In either case, the astronomical measurements point to new physics that have yet to be understood.

As the CMB passes through galaxy clusters, the clusters effectively leave "shadows" that allow astronomers to identify the most massive clusters in the universe, nearly independent of their distance.

"Clusters of galaxies are the most massive, rare objects in the universe, and therefore they can be effective probes to study physics on the largest scales of the universe," said John Carlstrom, the S. Chandrasekhar Distinguished Service Professor in Astronomy & Astrophysics, who heads the SPT collaboration.

"The unsurpassed sensitivity and resolution of the CMB maps produced with the South Pole Telescope provides the most detailed view of the young universe and allows us to find all the massive clusters in the distant universe," said Christian Reichardt, a postdoctoral researcher at the University of California, Berkeley and lead author of the new SPT cluster catalog paper.

The number of clusters that formed over the history of the universe is sensitive to the mass of the neutrinos and the influence of dark energy on the growth of cosmic structures.
"Neutrinos are amongst the most abundant particles in the universe," Benson said. "About one trillion neutrinos pass through us each second, though you would hardly notice them because they rarely interact with 'normal' matter."

The existence of neutrinos was proposed in 1930. They were first detected 25 years later, but their exact mass remains unknown. If they are too massive they would significantly affect the formation of galaxies and galaxy clusters, Benson said.

The SPT team has been able to improve estimates of neutrino masses, yielding a value that approaches predictions stemming from particle physics measurements.

"It is astounding how SPT measurements of the largest structures in the universe lead to new insights on the evasive neutrinos," said Lloyd Knox, professor of physics at the University of California at Davis and member of the SPT collaboration. Knox will also highlight the neutrino results in his presentation on Neutrinos in Cosmology at a special session of the APS on Tuesday, April 3.

NSF's Office of Polar Programs primarily funds the SPT. The NSF-funded Physics Frontier Center of the Kavli Institute for Cosmological Physics, the Kavli Foundation and the Gordon and Betty Moore Foundation provide partial support.