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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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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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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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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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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Experiment Observes Elusive Neutrino Transformation

Finding could help explain why the universe has more matter than antimatter

PASADENA, Calif.—An international team of physicists—including several from the California Institute of Technology (Caltech)—has detected and measured, for the first time, a transformation of one particular type of neutrino into another type. The finding, physicists say, may help solve some of the biggest mysteries about the universe, such as why the universe contains more matter than antimatter—a phenomenon that explains why stars, planets, and people exist at all.

The results, released online on March 8, come from the Daya Bay Reactor Neutrino Experiment, which consists of six 20-ton neutrino detectors lying beneath the mountains of southern China near Hong Kong. The paper in which the team reports its data has been submitted to the journal Physical Review Letters.

"Physicists working on five experiments around the world have been racing to measure this process," says Robert McKeown, professor of physics and leader of the Caltech team involved with the project. "Our precise measurement from the Daya Bay Experiment now provides the final clue in helping us understand neutrino transformations."

Neutrinos are fundamental, uncharged particles that zip through space at near-light speed, barely interacting with any other particles. In fact, billions of neutrinos are streaming through your body at this very second.

Neutrinos come in three types (or "flavors")—electron, muon, and tau—and can transform from one type to another via a process that is described by variables called mixing angles. There are three mixing angles, two of which have been previously measured; McKeown was part of the KamLAND experiment in Japan that helped determine the second of these mixing angles several years ago. But an accurate measurement of the third, called θ13 ("theta one three"), which describes how an electron neutrino transforms into the other flavors, has eluded physicists. Thanks to the Daya Bay Experiment, physicists have finally pinned down a precise number to describe the transformation.

Having measured all three mixing angles, physicists can now pursue the next set of ambitious experiments to study what is called CP violation, or charge-conjugation and parity violation, says McKeown. If CP violation is true, then particle reactions can occur at rates that differ from those of reactions involving the particles' antimatter counterparts.

In theory, the Big Bang should have produced equal amounts of matter and antimatter, with collisions between the two subsequently annihilating both. Had that been the case, however, there would be no stars, planets, people, or anything else made of matter. But CP violation, the thought goes, enabled the universe to have more matter than antimatter.

The Daya Bay Reactor Neutrino Experiment's six liquid-filled cylinders detect antineutrinos—the antimatter partner of the neutrino—produced by nuclear reactors in the nearby China Guangdong Nuclear Power Group. Three neutrino detectors sit about 400 meters (about a quarter of a mile) from the nuclear reactors, while the other three are located about 1700 meters (just over a mile) away.

The nuclear reactions that occur inside the energy-producing reactors produce electron antineutrinos, which can be observed by both sets of detectors. The far set of detectors measure fewer electron antineutrinos than expected because a fraction of the electron antineutrinos transform into muon and tau antineutrinos in mid-flight. The detectors cannot directly observe these muon or tau antineutrinos, but by measuring the fraction of "missing" electron antineutrinos, researchers can determine the θ13 mixing angle. In their experiments, the physicists found that the far set of detectors observed 6 percent fewer electron antineutrinos than expected, giving them the information needed to precisely calculate the value of θ13—which turned out to be 8.8 degrees.

McKeown and the Caltech group designed and built the calibration devices (three for each detector) that enabled their colleagues to understand how well the detectors would work and other crucial properties of the instruments.

The other Caltech members of the Daya Bay Collaboration are staff scientist Robert Carr, senior postdoctoral scholar in physics Dan Dwyer, Robert A. Millikan Postdoctoral Scholar in Experimental Physics Xin Qian, graduate student Hei Man (Raymond) Tsang, and postdoctoral scholar in physics Fenfang Wu. Funding for the Caltech team was provided by the National Science Foundation. The Daya Bay Collaboration involves nearly 300 researchers from 38 institutions around the world, with major contributions from—in addition to Caltech—China's Institute of High Energy Physics, Lawrence Berkeley National Laboratory, Brookhaven National Laboratory, and the University of Wisconsin, Madison.

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Vladimir Markovic Receives Clay Research Award

Caltech's Vladimir Markovic, professor of mathematics, has been chosen to receive the 2012 Clay Research Award from the Clay Mathematics Institute. 

He shares the prize with Brown University's Jeremy Kahn, who was previously an assistant professor of mathematics at Caltech. They were honored for their work in hyperbolic geometry.

At this year's Clay Research Conference in June at Oxford University, the institute will formally present Kahn and Markovic with the award, and both will present talks on their work.

For more information on the Clay Research Award, go to http://www.claymath.org.

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A Powerful New Astronomy Instrument Gets Ready for Hawaii

It's time to go to Hawaii—at least, if you're MOSFIRE, a new near-infrared spectrometer that's now on its way to the W. M. Keck Observatory, atop Mauna Kea. But the powerful new instrument, six feet in diameter, about a dozen feet in length, and weighing in at 4,500 pounds—10,000 if you include the mount and packing crate—isn't going there to surf. MOSFIRE, which stands for multi-object spectrometer for infrared exploration, will be the newest weapon in the Keck's arsenal to survey the cosmos, helping astronomers learn about star formation, galaxy formation, and the early universe. 

It's taken seven years to design and build MOSFIRE, which has made its home in the synchrotron high-bay facility at the southern edge of campus. Today, it's scheduled to leave Caltech for good and head to San Diego. There, it will board a boat on February 8 and cruise to Hilo, where it will be trucked up almost 14,000 feet to the peak of Mauna Kea.

MOSFIRE will take spectra—the chemical signatures of everything from stars to galaxies—at near-infrared wavelengths (0.97-2.45 microns, or millionths of a meter), which are just a bit longer than the light our eyes can see. Observing in the infrared allows researchers to probe stars and galaxies that are obscured in clouds of dust, as well as the most distant objects whose spectra have been shifted beyond optical wavelengths by the expansion of the universe. What sets MOSFIRE apart from other instruments is its superior sensitivity and ability to survey up to 46 objects at the same time. 

"There are only two or three instruments in the world that do something similar, but none are as sensitive and none are on telescopes as big as Keck's," says Chuck Steidel, the Lee A. DuBridge Professor of Astronomy at Caltech, and MOSFIRE's co-principal investigator. Steidel anticipates that MOSFIRE will be one of the Keck's workhorse instruments, used for about half of all telescope time. "It's opening up a whole new area of study," he says.

The instrument can scan the sky with a 6.1 arc minute field of view, which is about 20 percent of a full moon and nearly 100 times bigger than the Keck's current near-infrared camera. To take spectra of multiple objects, the state-of-the-art spectrometer consists of 46 pairs of sliding bars that open and close like curtains. Aligned in rows, each pair of bars blocks most of the sky, leaving a small slit between the bars that allows a sliver of light from the targeted object to leak through. Light from each slit then enters the spectrometer, which breaks down the object's light into its spectrum of wavelengths.

With its multiple-object capability, the new tool will make research in near-infrared spectroscopy many times more efficient than before. "I reckon that MOSFIRE will observe very faint targets more than a hundred times faster than has ever been possible," says Steidel, who does research on galaxy formation and observational cosmology. "All the observations that my group and I have done in near-infrared spectroscopy with Keck over the last ten years could be done in just one night with MOSFIRE."

Because everything that's even somewhat warm radiates in the infrared, all infrared instruments must be kept cold to prevent any trace of heat from the ground, the telescope, or the instrument itself from messing up the signal you're trying to detect. MOSFIRE is kept at a cool 120 kelvins (about -243 degrees Fahrenheit or -153 degrees Celsius), and will be the largest cryogenic instrument on the Keck telescopes.

Astronomers will use MOSFIRE to study the epoch of galaxy formation, as well as the so-called period of reionization, when the universe was just a half-billion to a billion years old. During this time, galaxies and quasars—objects consisting of huge black holes that spew enormous amounts of energy as they consume gas and dust—first turned on, shining brightly and ionizing the neutral gas between galaxies for the first time since the universe was only about 380,000 years old. The instrument will also be used to investigate nearby stars, young stars, how stars formed, and even brown dwarfs, which are stars not quite massive enough for nuclear fusion to ignite in their cores.

MOSFIRE will also allow astronomers to do riskier—but more scientifically rewarding—research, Steidel says. Taking the spectrum of single a star or galaxy involves precious telescope time and resources. But because MOSFIRE can observe many objects at once, astronomers can afford to take extremely long exposures. Otherwise, such long exposures of single targets would be too costly.

"I'm definitely ready to do science," says Steidel, whose graduate students have planned their PhD theses around MOSFIRE. "I learned a huge amount working on the instrument, and it has been a lot of fun, but my eye has always been on what we can do with it." No one's sure what astronomers will discover, but therein lies the excitement, he says. "Sometimes serendipity is the most interesting thing that happens."

In addition to Steidel, MOSFIRE is led by co-principal investigator Ian McLean of UCLA. Caltech's Keith Matthews, who has built two previous Keck instruments, plays a leading role as chief instrument scientist. The team includes the engineering and technical staff of the Caltech Optical Observatories, the technical staff of the UCLA Infrared Lab, staff from the W. M. Keck Observatory, and optical designer Harland Epps of UC Santa Cruz. MOSFIRE was supported by the National Science Foundation and a gift from Gordon and Betty Moore.  

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Radio Stars

Caltech's newest astronomy professor searches for cosmic radio waves

Growing up in rural northwest Ireland, beyond the reach of city lights, Gregg Hallinan fell in love with the night sky. "When you didn't have bad weather, and you didn't have clouds, the skies were nothing short of spectacular," he says. "From a young age, I was obsessed with astronomy—it's all I cared for. My parents got me a telescope when I was seven or eight, and from then on, that was it."

Now, Hallinan has brought his celestial obsession to Caltech as a new assistant professor of astronomy. He explores magnetic activity around stars, planets, and those in-between objects called brown dwarfs, which are balls of gas that just aren't big enough for nuclear fusion to ignite and turn them into stars. "I consider myself incredibly lucky that I can take my passion and hobby and have it as a career," he says.

Magnetic fields play important roles throughout the universe. In our own neighborhood, the sun's magnetic field causes all the features we see on its surface, like sunspots, solar flares, and long arcs of plasma called prominences. Earth's magnetic field forms a huge bubble that shields the planet from solar wind, which contains energetic particles that can strip the Earth of its ozone layer, our protection from harmful ultraviolet radiation. On Earth and other planets, like Jupiter, magnetic fields accelerate charged particles and slam them into the magnetic poles, creating light shows we know as the northern and southern lights.

Around stars, planets, and other astronomical objects, the accelerating particles also produce radio signals that travel across space. Hallinan's most surprising and important discovery yet was one he made as a graduate student at the National University of Ireland, Galway, when he found that brown dwarfs generate regular pulses of radio emissions—a feature more commonly associated with planets like Jupiter.

After receiving his PhD in 2008, he stayed at Galway as a postdoc for two years to follow up on his thesis work. He then spent five months at the National Radio Astronomical Observatory in Socorro, New Mexico, and a year at the University of California, Berkeley, before coming to Caltech.

Studying magnetic fields and the fleeting blips of radio emission they produce has led Hallinan to become increasingly interested in those signals, which are examples of a broader type of phenomenon called radio transients. All kinds of cosmic phenomena can generate these variable radio signals, such as exploding stars, mysterious blasts called gamma ray bursts, and stars being ripped apart when venturing too close to a black hole.

One of the most exciting sources of radio transients are planets around other stars, Hallinan says, and hunting for radio-emitting planets will be a major focus of his research. Radio pulses from an exoplanet would indicate the presence of a magnetic field, and since Earth's protective magnetic field may have been crucial for allowing life to evolve, radio activity from an exoplanet could be a signature for a habitable planet. "Looking very long term, when we're characterizing habitable planets, magnetic fields could be important constraints for trying to figure out if there's life on those planets," Hallinan says. But so far, he adds, no one has detected radio emission from any exoplanet. "I'm trying to be one of the pioneers in trying to detect that radiation."

"The radio transient sky is virtually unexplored," he says. "We know there's stuff happening out there, but we haven't yet got the technology to systematically search for those transients." But Hallinan is working to change that, helping to lead exactly such a search for radio emission from exoplanets and other kinds of radio transients. In particular, he's enlisting the most powerful radio telescope in the world to help with the search: the Jansky Very Large Array in New Mexico. He's also working to bring a radio-transient monitoring project to Caltech's Owens Valley Radio Observatory, east of the Sierra Nevada. And with other new radio telescopes coming on line—such as the Low Frequency Array in Europe and the Long Wavelength Array in New Mexico—discoveries are on their way, Hallinan says. That especially includes exoplanets. "We're very hopeful that we'll find radio emission from other planets in the next few years."

Caltech is already the home of the Palomar Transient Factory, a project led by professor of astronomy and planetary science Shri Kulkarni that surveys the skies for flashes of light in visible wavelengths, instead of radio. "Caltech is pretty much unparalleled in the study of transient science," Hallinan says, and a radio-transient project will expand on Caltech's expertise. "The most exciting thing about radio transient work is that we don't know what's out there. You're at the cutting edge."

Aside from astronomy, he's a big fan of mixed martial arts; back in Ireland, he was a karate instructor. But these days, Hallinan is focused on the cosmos, a passion first kindled on those clear winter nights above the Irish countryside.  

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