X-ray Telescope Takes First Image

NASA's NuSTAR space telescope has taken its first image, snapping a shot of the high-energy X rays from a black hole in the constellation Cygnus. NuSTAR—short for Nuclear Spectroscopic Telescope Array—was launched on June 13, and is the first telescope that can focus high-energy X rays. It will explore black holes, the dense remnants of dead stars, energetic cosmic explosions, and even our very own sun.

"Today, we obtained the first-ever focused images of the high-energy X-ray universe," says Fiona Harrison, a professor of physics and astronomy at Caltech and the mission's principal investigator, in a NASA press release. "It's like putting on a new pair of glasses and seeing aspects of the world around us clearly for the first time."

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Put a Seismometer in Your Living Room

Back in the 1960s, Charlie Richter (PhD '28) installed a seismometer in his living room. It was bigger than his TV set, and it didn't go with the sofa, but it saved him a lot of late-night drives into the Seismo Lab and was a great conversation piece. Now, if you live in the Pasadena area, you can have one, too. Professor of geophysics Robert Clayton will send a wallet-sized seismometer to the first 1,000 volunteers with an Internet connection and a spare USB port. There is one small catch: you have to promise to leave your computer on 24/7.

Even as you impress your friends by creating your own mini-quakes ("we encourage people to test the unit by jumping up and down," Clayton says with a grin), you'll be contributing to a serious civic project—creating block-by-block earthquake-intensity maps that can guide ambulances and fire trucks to hard-hit areas almost while the ground is still rolling. Ordinary seismic data won't do; as we learned in the 1994 Northridge earthquake, heavy damage can strike far from the epicenter.

Crowd-sourced seismology dates to the turn of the millennium, when David Wald (PhD '93), Vincent Quitoriano (BS '99), and Humboldt State's Lori Dengler created an online questionnaire called "Did You Feel It?" The site went viral with the magnitude 7.1 Hector Mine quake, and now even a shaker in the 4 to 5 range will generate some 50,000 responses. The first thing people do—we hope!—is take cover," Clayton says. "But the second thing they do, apparently, is log on and file a report. So we want to put instruments where the people are."

A collaboration between Caltech's seismology, earthquake engineering, and computer science departments, the Community Seismic Network was inspired by what Clayton calls "the densest urban array ever"—a multimillion-dollar array of 5,206 sensors, or better than one per block, that were buried under the grassy verges between the sidewalks and the streets of Long Beach and operated from January through June of 2011. The sensors were used by the Signal Hill Petroleum Company to map its holdings by analyzing how shock waves reflected off the rock formations deep underground. The preferred oil-field survey tool is a stick of dynamite, but working in a city called for a subtler approach—sort of. "They had to pull a parade permit every day," says Clayton. A train of 30-ton vibrator trucks would drive up and down the boulevards, rattling doors and windows, preceded by a police escort to clear the way.

The survey crew worked weekdays from 9:00 to 4:00, but the seismometers ran 24/7. The array straddled the Newport-Inglewood fault zone, the source of the disastrous 1933 quake that killed 115 people. "The earth is constantly chattering away down there," says Clayton, and the network caught hundreds of after-hours tremors, including a magnitude 2.4 under nearby Carson. A color-coded video of this hiccup shows the seismic waves propagating eastward block by block, station by station. The waves distort as they encounter the fault, whose segments reveal themselves as fleeting white scars in the sea of red and blue.

The cross-sectional renderings are even more revealing. Grad student Asaf Inbal projected the waveforms from an unfelt microquake back to their source in the fault plane. The resulting animation "looks like a summer lightning storm," Clayton says, but in this case, the towering cumulonimbus clouds are actually micro-slip zones, and the thunderbolts are transitory sub-centimeter displacements striking as deep as 20 kilometers underground.

Such detailed data will allow seismologists to answer "the big question," says Clayton: "How does an earthquake nucleate? Most activity simply dies out over very small distances. What lets something suddenly take off?"

Which brings us back to Pasadena. The Southern California Seismic Network, run jointly by Caltech and the U.S. Geological Survey, runs from San Luis Obispo to the Mexican border. It includes about 40 stations in the Greater Los Angeles region, or about one every 10 kilometers; each state-of-the-art installation costs $100,000. The Community Seismic Network uses mass-produced accelerometer chips like the ones in your Wii, each costing about a hundred bucks. High-end they're not. In fact, Clayton says, "no single sensor would have impressively seen any one event. But collectively, when you have 100 of them, you see it."

Given enough sensors, you can assess seismic hazards block by block, and in some cases floor by floor. Caltech's Millikan Library, for example, has sensors on each of its nine floors, plus one on the roof and one in the basement. Undergrad Hong Sheng and senior research fellow Monica Kohler (PhD '95) used that data to create a 3-D rendering of the building's response to the magnitude-4.2 Newhall quake of September 1, 2011. Watching the library's energetic hula is rather unsettling, especially if you hang out on Millikan's middle floors; fortunately, the scale is greatly exaggerated and the actual sway is less than a tenth of a millimeter. Similar animations could alert inspectors to hidden damage after a large earthquake, Clayton says. Tall buildings sway at frequencies determined by the details of their construction, so "if this frequency drops during an event and doesn't bounce back once the shaking stops, it could be a sign of broken welds. We saw this in the Northridge earthquake."

Little by little, Clayton hopes to grow the Community Seismic Network to 15,000 sensors spanning the Los Angeles basin, from the Hollywood Hills to Lake Forest in southern Orange County. But for now he just wants to fill the area bounded by the San Gabriel Mountains and the 605, 10, and 2 freeways. Be the first one on your block—sign up today!

The Community Seismic Network is funded by the Gordon and Betty Moore Foundation and by Caltech trustee Ted Jenkins (BS '65, MS '66).

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Doug Smith
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NuSTAR Space Telescope Blasts Off

Caltech-led mission will explore the X-ray universe

This morning, NASA's NuSTAR telescope was launched into the low-Earth orbit from which it will begin exploring the high-energy X-ray universe to uncover the secrets of black holes, the dense remnants of dead stars, energetic cosmic explosions, and even our very own sun.   

The space telescope—the most powerful high-energy X-ray telescope ever developed—rode toward its destination inside the nose of a Pegasus rocket strapped onto the belly of a "Stargazer" L-1011 aircraft. Around 9:00 a.m. (PDT), the plane—which had earlier taken off from the Kwajalein Atoll in the western Pacific—dropped the rocket from an altitude of 39,000 feet. The rocket was in free fall for about five seconds before the first of its three stages ignited, blasting NuSTAR into orbit around the equator.

"NuSTAR will open a whole new window on the universe by being the very first telescope to focus high-energy X rays," says Fiona Harrison, professor of physics and astronomy at Caltech and the principal investigator of the NuSTAR mission. The telescope is 100 times more sensitive than any previous high-energy X-ray telescope, and it will make images that are 10 times sharper than any that have been taken before at these energies, she says. 

NuSTAR—short for "Nuclear Spectroscopic Telescope Array"—can make sensitive observations of cosmic phenomena at higher frequencies than other X-ray telescopes now in orbit, including NASA's Chandra X-Ray Observatory and the European Space Agency's XMM-Newton observatory. X rays are at the high-frequency end of the electromagnetic spectrum, and can be thought of as light particles called photons that carry a lot of energy. Chandra and XMM-Newton can detect X rays with energies up to about 10,000 electron volts (eV); NuSTAR will be able to see photons with energies up to 78,000 eV. By comparison, the energy of visible light is just a few eVs, while the X rays used to check for broken bones have energies on the order of hundreds of thousands of eVs.

High-energy X rays can penetrate skin and muscle because they carry so much energy. But that also means that they are hard to reflect. The mirrors in optical telescopes cannot be used to reflect and focus X rays. Instead, X-ray telescopes can only reflect incoming X rays at very shallow angles. These photons travel on paths that are almost parallel to the reflective surface, like rocks skipping on a pond. To reflect enough X rays for the detectors to observe, telescopes must use nested cylindrical shells that focus the photons onto a detector. Chandra has four such nested shells; XMM-Newton has 58. NuSTAR, in contrast, has 133, providing unprecedented sensitivity and resolution.

Each of NuSTAR's nested shells is coated with about two hundred thin reflective layers, some merely a few atoms thick, composed of either high-density materials, such as tungsten and platinum, or low-density materials like silicon and carbon. By alternating the two types of layers, NuSTAR's designers have produced a crystal-like structure that reflects high-energy X rays. Harrison and her group at Caltech started developing this technology more than 15 years ago and first tested it in a balloon experiment called the High-Energy Focusing Telescope (HEFT) in 2005. 

Fiona Harrison, professor of physics and astronomy at Caltech, is the principal investigator of the NuSTAR mission.
Credit: Lance Hayashida

A telescope focuses light by bending it so that it converges onto one spot—an eyepiece or a detector. But because X rays can only be reflected at such shallow angles, they do not converge very strongly. As a result, the distance between an X-ray telescope's mirrors and the detector must be especially long for the X rays to focus. Chandra is 45 feet long and XMM-Newton is about 30 feet long—as big as buses. NuSTAR—funded under NASA's Explorers program, which emphasizes smaller, cheaper missions that do science as efficiently as possible—has a deployable mast that allows it to squeeze inside the Pegasus rocket's roughly seven-foot-long payload compartment. About a week after launch, the mast will unfold and stretch to more than 30 feet. 

This new technology, Harrison explains, "will allow NuSTAR to study some of the hottest, densest, and most energetic phenomena in the universe." Black holes are a key target of the telescope. Just 20 years ago, she says, black holes were thought to be rare and exotic, but "today we know that every galaxy has a massive black hole in its heart." Our own Milky Way galaxy, with a black hole four million times as massive as our sun, is no exception. Gas and dust block most of our view of the galactic center, but by observing in high-energy X rays, NuSTAR can peer directly into the heart of the Milky Way. 

Disks of gas and dust surround many of the supermassive black holes of other galaxies. As the material spirals into these black holes, which are millions to billions of times as massive as the sun, the regions closest to the black hole radiate prodigious amounts of high-energy X rays, which are visible even if the black hole is hidden behind dust and gas. NuSTAR will therefore allow astronomers to not only conduct a census of all the black holes in the cosmic neighborhood, but also to study the extreme environments around the black holes. Astronomers will even be able to measure how fast black holes spin, which is important for understanding how they form and their role in the history and evolution of their host galaxies. 

Astronomers will also point NuSTAR at supernovae remnants, the hot embers left over from exploded stars. After a star burns through all of its fuel, it blows up, blasting material out into space. In that explosion, new elements are formed (in fact, many of the heavier elements on Earth were forged long ago in stars and supernovae). Some newborn atoms are radioactive, and NuSTAR will be able to detect this radioactivity, allowing astronomers to probe what happens during the fiery death of a star. 

The telescope also will devote some time to the observation of our own star, the sun. The outer layer of the sun, called the corona, burns at millions of degrees. Some scientists speculate that nanoflares—smaller versions of the solar flares that occasionally erupt from the solar surface—keep the corona hot. NuSTAR may be able to see nanoflares for the first time. "In a few hours of observations, NuSTAR will answer this longstanding question that solar physicists have been scratching their heads about for years," says Daniel Stern of NASA's Jet Propulsion laboratory, NuSTAR's project scientist.

In July, NuSTAR will start taking data, revealing a whole new X-ray universe—shining, shimmering, and splendid—to scientists. "We expect amazing discoveries from it," Stern says.

The NuSTAR mission is led by Caltech and managed by JPL for NASA.

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Caltech Graduate Student Wins DOE Fellowship for Computational Science

Caltech graduate student Melissa Yeung has been selected as one of 21 students nationally to receive a Department of Energy (DOE) Computational Science Graduate Fellowship this year. The honor covers up to four years of support for graduate studies in fields that focus on the use of high-performance computing technology to solve complex problems in science and engineering.

The DOE Computational Science Graduate Fellowships are jointly funded by the Office of Science and National Nuclear Security Administration's Office of Defense Programs. In addition to covering tuition and providing an annual stipend, the award gives students an opportunity to spend a summer at a DOE national laboratory doing computational research in a field that is unrelated to their thesis work. 

As part of Caltech's Applied Geometry Lab, Yeung studies an area of mathematics known as discrete differential geometry, which has diverse applications in such fields as engineering, computer animation, product design, and medicine. As a second-year graduate student in mathematics, Yeung says she feels incredibly fortunate to be at Caltech, where she has been given the freedom to work across divisions; although she is enrolled in the Division of Physics, Mathematics and Astronomy, she is now being advised by Mathieu Desbrun, professor of computing and mathematical sciences from the Division of Engineering and Applied Science.

"'What do you get when a mathematician and a computer scientist meet?' is usually the beginning of a bad joke. At Caltech, it's instead the start of a great collaboration," says Desbrun, who is also the director of Computing and Mathematical Sciences and Information Science and Technology. "Working with Melissa offers new perspectives that computer scientists like myself are not frequently presented with." 

Yeung is the second student from Caltech's Applied Geometry Lab to receive a DOE Computational Science Graduate Fellowship in recent years. In 2010, Evan Gawlik, who completed his senior thesis with Desbrun, also received the honor.

Yeung traces the beginnings of her interest in computational geometry to a lecture that she happened to pop into at a conference a few months before she came to Caltech. In that lecture, she heard about how computational topology could be used to analyze complex datasets, identifying underlying shape characteristics that bring new understanding to a problem.

Shortly after arriving at Caltech, while flipping through the course catalog, Yeung came across a course offered by Desbrun on discrete differential geometry and started sitting in on the lectures. And that was it: she was hooked. "I think math is beautiful, but at times it seems that the more math I do, the more disconnected from the world I feel. It has been really gratifying for me to see all of this math that I thought was so incredibly abstract so immediately applicable."

 

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Kimm Fesenmaier
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Physicists Close in on a Rare Particle-Decay Process

Underground Experiment May Unlock Mysteries of the Neutrino

PASADENA, Calif.—In the biggest result of its kind in more than ten years, physicists have made the most sensitive measurements yet in a decades-long hunt for a hypothetical and rare process involving the radioactive decay of atomic nuclei.

If discovered, the researchers say, this process could have profound implications for how scientists understand the fundamental laws of physics and help solve some of the universe's biggest mysteries—including why there is more matter than antimatter and, therefore, why regular matter like planets, stars, and humans exists at all.

The experiment, the Enriched Xenon Observatory 200 (EXO-200), is an international collaboration that includes the California Institute of Technology (Caltech) and is led by Stanford University and the SLAC National Accelerator Laboratory, a U.S. Department of Energy (DOE) National Laboratory.

The EXO-200 experiment has placed the most stringent constraints yet on the nature of a so-called neutrinoless double beta decay. In doing so, physicists have narrowed down the range of possible masses for the neutrino, a tiny uncharged particle that rarely interacts with anything, passing right through rock, people, and entire planets as it zips along at nearly the speed of light.

The collaboration, consisting of 80 researchers, has submitted a paper describing the results to the journal Physical Review Letters.

In a normal double beta decay, which was first observed in 1986, two neutrons in an unstable atomic nucleus turn into two protons; two electrons and two antineutrinos—the antimatter counterparts of neutrinos—are emitted in the process.

But physicists have suggested that two neutrons could also decay into two protons by emitting two electrons without producing any antineutrinos. "People have been looking for this process for a very long time," says Petr Vogel, senior research associate in physics, emeritus, at Caltech and a member of the EXO-200 team. "It would be a very fundamental discovery if someone actually observes it."

A neutrino is inevitably produced in a single beta decay. Therefore, the two neutrinos that are produced in a neutrinoless double beta decay must somehow cancel each other out. For that to happen, physicists say, a neutrino must be its own antiparticle, allowing one of the two neutrinos to act as an antineutrino and annihilate the other neutrino. That a neutrino can be its own antiparticle is not predicted by the Standard Model—the remarkably successful theory that describes how all elementary particles behave and interact.

If this neutrinoless process does indeed exist, physicists would be forced to revise the Standard Model.

The process also has implications for cosmology and the origin of matter, Vogel says. Right after the Big Bang, the universe had the same amount of matter as antimatter. Somehow, however, that balance was tipped, producing a slight surplus in matter that eventually led to the existence of all of the matter in the universe. The fact that the neutrino can be its own antiparticle might have played a key role in tipping that balance.

In the EXO-200 experiment, physicists monitor a copper cylinder filled with 200 kilograms of liquid xenon-136, an unstable isotope that, theoretically, can undergo neutrinoless double beta decay. Very sensitive detectors line the wall at both ends of the cylinder. To shield it from cosmic rays and other background radiation that may contaminate the signal of such a decay, the apparatus is buried deep underground in the DOE's Waste Isolation Pilot Plant in Carlsbad, New Mexico, where low-level radioactive waste is stored. The physicists then wait to see a signal.

The process, however, is very rare. In a normal double beta decay, half of a given sample would decay after 1021 years—a half-life roughly 100 billion times longer than the time that has elapsed since the Big Bang.

One of the goals of the experiment is to measure the half-life of the neutrinoless process (if it is discovered). In these first results, no signal for a neutrinoless double beta decay was detected in almost seven months' of data—and that non-detection allowed the researchers to rule out possible values for the half-life of the neutrinoless process. Indeed, seven months of finding nothing means that the half-life cannot be shorter than 1.6 × 1025 years, or a quadrillion times older than the age of the universe. With the value of the half-life pinned down, physicists can calculate the mass of a neutrino—another longstanding mystery. The new data suggest that a neutrino cannot be more massive than about 0.140 to 0.380 electron volts (eV, a unit of mass commonly used in particle physics); an electron, by contrast, is about 500,000 eV, or about 9 × 10-31 kilograms.

More than ten years ago, the collaboration behind the Heidelberg-Moscow Double Beta Decay Experiment controversially claimed to have discovered neutrinoless double beta decay using germanium-76 isotopes. But now, the EXO-200 researchers say, their new data makes it highly unlikely that those earlier results were valid.

The EXO-200 experiment, which started taking data last year, will continue its quest for the next several years.

The EXO collaboration involves scientists from SLAC, Stanford, the University of Alabama, Universität Bern, Caltech, Carleton University, Colorado State University, University of Illinois Urbana-Champaign, Indiana University, UC Irvine, Institute for Theoretical and Experimental Physics (Moscow), Laurentian University, the University of Maryland, the University of Massachusetts–Amherst, the University of Seoul, and the Technische Universität München. This research was supported by the DOE and the National Science Foundation in the United States, the Natural Sciences and Engineering Research Council in Canada, the Swiss National Science Foundation, and the Russian Foundation for Basic Research. This research used resources of the National Energy Research Scientific Computing Center (NERSC).

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Marcus Woo
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Notes from the Back Row: "An Explosion of Explosions"

"I'm looking for things that go bump, burp, or boom in the sky," says astronomer Shrinivas "Shri" Kulkarni, noting that "there is one supernova somewhere in the universe every second." A supernova is the brilliant new object we see when a star explodes, and if that star happens to go off in the nighttime skies over California, the odds are pretty good he'll find it. In his Watson Lecture given on April 25, 2012, Kulkarni, Caltech's John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science and the director of the Caltech Optical Observatories, described how Caltech's fully automated Palomar Transient Factory—Kulkarni calls it "Transients 'R' Us"—is revolutionizing how we explore the changing sky.

Supernovae fade into oblivion within days, or at best a few months. Catching them while they're bright is a matter of looking in the right direction at the right time—which is what a vast network of telescopes, many of them in the back yards of dedicated amateur astronomers, are doing right now. But the Transient Factory, says Kulkarni, was the first to create a sort of chain in which a discovery by the dedicated wide-field survey telescope automatically directs a larger telescope to zoom in for a closer look that same night; if the second telescope is intrigued by what it sees, the humans are notified so that even bigger telescopes can be brought to bear. "The hardware is, in fact, the smallest part of the cost," Kulkarni says. "The most expensive component is grayware." Now, with the software pipeline up and running, it's time to "go out and look for weird things," says Kulkarni, whose trophies over the years include the discovery of the first millisecond pulsar and the first brown dwarf. The weird things the Factory is finding will make a nice addition to the collection—watch the talk to get a glimpse of them.

"An Explosion of Explosions" is available for download in HD from Caltech on iTunesU. (Episode 11)

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Doug Smith
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Overactive Black Holes Shut Down Star Formation

A team of astronomers has found that the most active galactic nuclei—enormous black holes that are violently devouring gas and dust at the centers of galaxies—may prevent new stars from forming. The team, which includes several researchers from Caltech, reported its findings in the May 10 issue of the journal Nature.

Supermassive black holes—which are more than a million times as massive as the sun—are found at the cores of nearly all large galaxies. As gas and dust fall into the behemoth, the material heats up and produces tremendous amounts of energy, radiating X rays. Previous observations have suggested that black holes with higher activity—and therefore brighter X-ray radiation—trigger more stars to form in their galaxies.

But using the Herschel Space Observatory, the astronomers have now discovered that if the black hole is too active, it appears to shut down star formation. What may be happening, the astronomers say, is that, at first, the infalling gas and dust can clump together and make new stars. But if you feed the black hole too much, the material gets so hot that the resulting radiation blasts the surrounding gas away. Without enough raw materials, new stars can no longer form.

While astronomers previously have seen black holes suppress star formation in a few individual galaxies, these new results are based on observations of 65 galaxies, says Joaquin Vieira, a postdoctoral scholar in physics at Caltech and coauthor of the paper. Instead of just studying a specific case, the researchers looked at the aggregate properties of a large sample. "This is an important and unexpected result that could have only been shown with a large and cohesive survey," adds James Bock, a senior faculty associate at Caltech and cocoordinator of the Herschel survey.

To learn more, click here

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Marcus Woo
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Notes from the Back Row: "Electrons In Flatland"

Quantum mechanics prides itself on its weirdness. Waves are particles, particles are waves, and nothing is anything until you measure it, at which point an infinity of possibilities collapses into one more-or-less solid certainty. And what happens when you have weird things acting in large groups? Even weirder things, says Caltech physicist James Eisenstein. Eisenstein should know; the Frank J. Roshek Professor of Physics and Applied Physics studies the quantum-mechanical equivalent of flash mobs—or, as they're known to physicists, "emergent systems." These are not wild gleams in a theoretician's eye, either—the "Flatland" in the title refers to the two-dimensional logic gates found by the billion in every smartphone, iPod, or other high-tech gadget. In his Watson lecture on January 18, 2012, he uses vivid analogies and nifty animations to lead us through the basics of quantum electronics to his own work with some very bizarre particles—even for quantum mechanics. Could these particles form the basis of a computer that uses the laws of quantum mechanics to solve otherwise unsolvable problems? Watch the lecture and find out!

"Electrons in Flatland" is available for download in HD from Caltech on iTunes U. (Episode 7)

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Doug Smith
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Fermi Space Telescope Helps Scientists Narrow Search for Dark Matter

Scientists have further narrowed the search for a hypothetical particle that could be dark matter, the mysterious stuff that makes up 80 percent of all the mass in the universe. Caltech postdoc Jennifer Siegal-Gaskins presented the researchers' results, compiled from two years' worth of data from NASA's Fermi Gamma-ray Space Telescope, at a meeting of the American Physical Society in Atlanta earlier this week.

Gamma rays are very energetic light, and the telescope looks for faint gamma-ray signals that are generated by a variety of sources, such as gas and dust spiraling into supermassive black holes or exploding stars. But another potential source of gamma rays is dark matter. Although no one is sure what dark matter is, one of the leading candidates is a yet-to-be-discovered particle called a weakly interacting massive particle (WIMP). When two of these WIMPs meet, the theory goes, they can annihilate one another and generate gamma rays.

There are many possible versions of WIMPs, and they're expected to span a wide range of masses, producing a range of gamma rays with different energies. Using Fermi, the scientists focused on 10 small galaxies that orbit the Milky Way, searching for gamma-ray signals within a specific range of energies. They found no signs of annihilating WIMPs, which rules out certain kinds of WIMPs as dark-matter candidates.

To read more and to watch videos explaining the results, click here

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Marcus Woo
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Astronomers Find Light-Bending Quasars

Astronomers have found celestial objects called quasars that bend and distort the light coming from galaxies behind them. The discovery may finally allow astronomers to determine the masses of galaxies that host quasars.

"No one has done this before," says George Djorgovski, a professor of astronomy at Caltech and member of the research team. "It would be surprising—but very interesting—if these galaxies turn out to be systematically different from the general galaxy population."

This light-bending effect, called gravitational lensing, is normally seen in the reverse orientation: foreground galaxies distorting the light of background quasars. (Caltech's Fritz Zwicky was the first to propose that gravitational lensing could be used to study distant clusters of galaxies in 1937, but it wasn't until 1979 that astronomers observed the phenomenon in a galaxy cluster that bent the light of a background quasar.)

The research, led by astronomers at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, is described in a paper accepted for publication in the journal Astronomy and Astrophysics. The team discovered the first light-bending quasar in 2010, but now they have found three more—and the data is even better. 

Quasars are the active centers of galaxies with supermassive black holes—those millions or billions of times more massive than our sun—that gobble up surrounding gas and dust. The material heats up as it spirals into the black hole, churning out enormous amounts of energy, making quasars some of the most powerful and brightest objects in the universe.

They're so bright, in fact, that they outshine their host galaxies, making it nearly impossible for astronomers to see anything around them. But by using a combination of adaptive optics—a technique that improves image resolution by removing the blur from the atmosphere—at Keck Observatory and the Hubble Space Telescope, the astronomers were able to detect faint arcs around the quasar. The arcs are the background galaxies distorted by the foreground quasars.

The brightness of quasars prevents astronomers from measuring the masses of their host galaxies with traditional approaches, which are based on the galaxies' internal dynamics—for example, how the stars move. But the light-bending quasars provide a different way to determine their host-galaxy masses. The more massive the host galaxies, the more they warp the light emitted by the background galaxies. By measuring how much the light bends, astronomers can infer the host galaxies' masses. 

In addition to Djorgovski, the other Caltech researcher is Ashish Mahabal, a staff scientist in computational astronomy. Other researchers include Frédéric Courbin, Cécile Faure, François Rerat, Malte Tewes, and Georges Meylan of EPFL; Daniel Stern of NASA's Jet Propulsion Laboratory; Todd Boroson of National Optical Astronomy Observatories; Dominique Sluse of Bonn University; and Dheeraj Pasham of the University of Maryland.

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