From Spinning Black Holes to Exploding Stars: A New View of the Energetic Universe

Watson Lecture Preview

The Nuclear Spectroscopic Telescope Array, or NuSTAR, sees the high-energy X-rays emitted by the densest, hottest regions of the universe. The brainchild of Fiona Harrison, Caltech's Benjamin M. Rosen Professor of Physics and Astronomy and NuSTAR's principal investigator, the phone-booth-sized NuSTAR was launched from beneath an airplane's wing, unfolding to the length of a school bus once in orbit. Professor Harrison will describe NuSTAR's unlikely journey and share some of its remarkable results at 8:00 p.m. on Wednesday, December 4, in Caltech's Beckman Auditorium. Admission is free.

 

Q: What's "new" about NuSTAR?

NuSTAR is the first focusing high-energy X-ray telescope. X-rays can be focused by reflection, but they're so penetrating that they only reflect at very glancing angles—sort of like skipping a stone off the surface of a lake. But most of the X-rays don't interact even then, so you use "nested optics," which you can think of as a set of cones nested inside one another like Russian dolls. Each cone intercepts some of the X-ray beam. The higher the energy, the more glancing the reflecting angle is, and the more cones you need.

Other focusing telescopes, such as NASA's Chandra X-ray Observatory and the European Space Agency's X-ray Multi-Mirror Mission, observe X-rays with energies below about 10 kilo-electronvolts. NuSTAR can see up to 79 kilo-electronvolts. Chandra has four nested mirrors, each about an inch thick and set at about a one-degree angle; NuSTAR has 133 mirrors as thin as my fingernail and almost parallel to the incoming light. We developed the detector here at Caltech. It's a digital camera, but made out of a special material that stops the high-energy X-rays that would have gone straight through previous X-ray imaging detectors.

NuSTAR is hundreds of times more sensitive, and its images are 10 times crisper than its nonfocusing predecessors, which basically worked like the pinhole camera you may have used to watch a solar eclipse. So we're able to observe the universe to much greater depth and in much greater detail than has previously been possible.

 

Q: What does NuSTAR see that we wouldn't see at other wavelengths?

A whole variety of things.

Medical X-rays are about 60 kilo-electronvolts, which is in the band that we observe. They penetrate the skin but stop in the bones, casting a shadow that shows up on the film. Similarly, we can look into the hearts of galaxies with high-energy X-rays, which penetrate the clouds of dust and gas where low-energy X-rays would be absorbed. We can see supermassive black holes, or rather the X-rays emitted by the very hot stuff falling into them. We can see neutron stars, which are the collapsed cores of burned-out stars so dense that a teaspoon of neutron star would weigh more than all of humanity. We can see the remnants of dead, exploded stars.

 

Q: What is your role in all this?

A: I built a pinhole-camera-type X-ray telescope as part of my PhD work at Berkeley in the early '90s, but I needed something much more sensitive to do what I really wanted to do. So I came down to Caltech, and we began developing NuSTAR's technology for a balloon experiment called the High-Energy Focusing Telescope, or HEFT. HEFT flew in 2005 and was so successful that we submitted a proposal to NASA's Small Explorer program to build a space version. As the principal investigator, I was responsible for putting the team together that proposed NuSTAR to NASA, and for overseeing the construction and launch. Now I lead the science team, which decides what to look at and analyzes all the data. Our primary mission ends in 2014, so right now I'm starting to write a proposal to extend the mission for another two years as a guest-investigator program open to anyone anywhere in the world.

I hope NuSTAR keeps me busy for another 10 years or more. There are no expendables such as cryogenic coolant, so it's a matter of how long the orbit lasts. We do experience atmospheric drag, so NuSTAR will eventually reenter and burn up. Either that, or something will break. As a small, inexpensive mission, we don't have redundant systems. If something breaks, there's no backup to switch over to.

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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Douglas Smith
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Peering Through the Intergalactic Dust

Caltech Builds a New Submillimeter Telescope in the Atacama Desert

Where do you go to look at the stars? Away from city lights, certainly. But if you're serious about peering far out into space, to the observable edges of our universe, at submillimeter wavelengths, you have to do a little better than that. You have to go farther and higher, up to where the atmosphere is thin. And if you want to look at the stars for more than a few nights a year, you also need some place that is very, very dry. Clouds, of course, obstruct the view of stars and galaxies, but even water vapor in the atmosphere can interfere with incoming electromagnetic radiation.

One of the most hospitable places for astronomy is also among the least hospitable for human life: the Atacama Desert in northern Chile, at high elevations. The Atacama is the driest desert on Earth, receiving perhaps a half an inch of rain each year (and in some locations, none at all). Because the region has been arid for so long, its mountain peaks rarely have glaciers or permanent snow coverage. The desert extends from the sea up toward the highest western ridge of the Andes. Even at the coast, the human population is sparse. But the very best conditions for submillimeter astronomy are found higher up.

The summit of Cerro Chajnantor, at an altitude of 5,617 meters (nearly 18,500 feet), is the proposed site for a new telescope known only by an acronym: CCAT. CCAT is a 25-meter telescope that observes electromagnetic radiation at wavelengths a little shorter than a millimeter—that is, wavelengths a thousand times longer than optical light. Because water vapor so strongly absorbs submillimeter-wave radiation, the ultradry Atacama Desert has been the go-to location for submillimeter telescopes for several decades. Indeed, from its perch on Cerro Chajnantor, the future CCAT will look down on a veritable forest of telescopes on the plateau some 600 meters below. To the northwest, the Atacama Pathfinder Experiment (APEX) and Atacama Cosmology Telescope (ACT) are visible; to the east are the Japanese Atacama Submillimeter Telescope Experiment (ASTE) and NANTEN telescopes; immediately below are the 66 telescopes in the Atacama Large Millimeter/submillimeter Array (ALMA).

So why truck up an extra 600 meters above the plateau in a cold, uninviting landscape over a rough dirt road to build CCAT? Surprisingly, the even thinner, drier air at the summit buys scientists a 1.4-fold increase in sensitivity over telescopes located on the plateau. It is "the driest high-altitude site to which one can drive a truck," says Riccardo Giovanelli, project director for CCAT.

The electromagnetic radiation that reaches us on Earth in the visible range of the light spectrum has always fascinated humans, because we can see it with our own eyes, or with the enhanced eye of an optical telescope. But electromagnetic radiation that comes to Earth at longer wavelengths has its own stories to tell about the universe. Most of the radiation emitted by stars falls in the ultraviolet (UV) and optical range, and can be detected by a traditional optical telescope (provided the telescope is sensitive enough). But in dusty clouds, where stars most often form, newborn stars are obscured and become invisible to an optical telescope. Fortunately, however, this UV and optical radiation from the new stars heats up the dust. The dust absorbs the star's UV and optical radiation, and reemits it into the universe at longer submillimeter wavelengths. By measuring the submillimeter radiation from the clouds, astronomers can learn about the stars that are hidden within.

There is widespread agreement in the scientific community that it is urgent to move forward with CCAT. In its 2010 Astronomy and Astrophysics Decadal Survey, the National Research Council of the National Academy of Sciences urged CCAT "to progress promptly to the next step in its development because of its strong science case … and its readiness." CCAT is drawing toward the close of its design phase. Construction should begin in 2014; first light—that is, the first scientific use of the instrument—is scheduled for 2019.

Lead engineer on the CCAT project is Stephen Padin, senior research associate in astrophysics at Caltech. According to Tom Soifer, chair of Caltech's Division of Physics, Mathematics, and Astronomy, Padin is "the only person on Earth with the experience and brilliance to build CCAT." During Padin's decades-long career as a vagabond telescope builder, he has helped to design and construct Antarctica's South Pole Telescope and the radio dishes that comprise the Owens Valley Radio Observatory. But the Atacama Desert, where Padin engineered the Cosmic Background Imager (CBI) telescope for Caltech 20 years ago, has a special allure for him. "It looks just like pictures of the martian surface," Padin says, "except the sky is a deep blue above the desert, while it is orange on Mars." Padin remembers one night on-site in Chile looking through a 6-inch refracting telescope while taking some measurements to adjust the CBI's pointing mechanism: "The view was astounding. Sharp, bright, and with a snap that no picture on a page or computer screen could ever hope to achieve."

At 25 meters in diameter, the CCAT telescope is substantially larger than both the next-largest submillimeter telescope, the 15-meter James Clerk Maxwell Telescope (JCMT) atop Hawaii's Mauna Kea, and the Herschel Space Observatory, which is a mere 3.5 meters in diameter. Like JCMT, CCAT will have a segmented mirror constructed of machined aluminum, a material that is lightweight and very reflective. The structure supporting the mirror will be built of carbon-fiber-reinforced plastic, which is light, stiff, and stable. Submillimeter telescopes are at a bit of an advantage over optical telescopes when it comes to procuring the necessary materials. Because telescopes like CCAT are designed to detect longer wavelengths of electromagnetic radiation, they can tolerate a somewhat rougher surface than optical telescopes. Optical telescopes must have a glass mirror and a steel structure to support that weight, while submillimeter telescopes can be constructed of lighter, less expensive materials.

To construct the mirror, the aluminum segments must be carefully machined and then accurately mounted on the support structure. Then the telescope must be installed on Cerro Chajnantor, which, at present, can only be reached via a road that is narrow, steep, and winding. To get to the top, says Padin, "you'll have to stop and roll a few boulders out of the way." Although the existing road will be widened before CCAT is installed, it will never be paved. (However, Padin notes, the Cerro Chajnantor road will be "a considerable improvement over access to Mount Wilson when the 60-inch reflecting telescope was built. Many of those parts were hauled up by mule teams.")

"The main issues for the CCAT site are that it's remote, and people can't breathe up there," Padin says. "Remote is always a problem for projects in astronomy, because you've got to get a lot of high-technology stuff to the middle of nowhere and then make it work. But in this case, you also have to factor in the effects of the altitude. People don't think very well at 18,500 feet." Indeed, the site is halfway to the altitude of a typical passenger airplane, and that means workers will be breathing in only about half the oxygen they would take in at sea level. To offset the effects of the altitude, workers will be required to use supplementary oxygen.

Leveling the site and producing an enclosure for CCAT will be handled by local Chilean companies, while scientific instruments and the pieces of the telescope itself—approximately 500 metric tons of equipment being developed and built all over the world—will be shipped in by sea. Then the entire telescope will be put together "at lower altitude," Padin explains, "where the scientists can think." At this stage, the team will verify that all of the components fit together properly and fix any minor problems. "It's embarrassing if you get on top of the mountain with a big pile of bits that don't fit," Padin says. After this test assembly, CCAT will be dismantled and trucked up to the summit of Cerro Chajnantor where it will be assembled for a second time.

Following construction, CCAT will be a fully automated observatory. In principle, says Padin, "you'll be able to sit at home with your laptop and drive the telescope." Except when problems arise or maintenance is required, the site will be uninhabited when CCAT is making observations. Padin laments the loss of "one of the big attractions for astronomy: traveling to exotic places and doing strange things in the middle of the night." Still, he admits, going to a mountain in the Atacama Desert "is fun the first time," but it becomes "less appealing as time goes on."

By peering into the submillimeter, CCAT will give us new eyes on the universe and help to resolve some pressing questions about star and galaxy formation. As Padin explains, "Astronomy is in an interesting position at the moment. We know a lot about the nearby stuff. We've spent hundreds of years looking at that at optical wavelengths. And now we actually know quite a bit about cosmology from measuring the microwave background left behind by the Big Bang. We know less about what happened in the middle, about the first stars turning on, the first galaxies forming. What happened between the smooth Big Bang and the very lumpy structure that we see now? This is the question that the next generation of telescopes, including CCAT, promises to address."

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Cynthia Eller
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Himiko and the Cosmic Dawn

Hubble and ALMA Observations Probe the Primitive Nature of a Distant "Space Blob"

The Subaru Telescope, an 8.2-meter telescope operated by the National Astronomical Observatory of Japan, has been combing the night sky since 1999. Located at the Mauna Kea Observatories in Hawaii, the telescope has been systematically surveying each degree of space, whether it looks promising or not, in search of objects worthy of further investigation. One of the most fascinating objects to emerge from the Subaru Telescope's wide-field survey—Himiko—was discovered in 2009. Himiko, a "space blob" named after a legendary queen from ancient Japan, is a simply enormous galaxy, with a hot glowing gaseous halo extending over 55,000 light-years. Not only is Himiko very large, it is extraordinarily distant, seen at a time approximately 800 million years after the Big Bang, when the universe was only 6 percent of its present size and stars and galaxies were just beginning to form.

How could such an early galaxy have sufficient energy to power such a vast glowing gas cloud? In search of the answer to this question, Richard Ellis, the Steele Family Professor of Astronomy at Caltech, together with colleagues from the University of Tokyo and the Harvard-Smithsonian Center for Astrophysics, undertook an exploration of Himiko using the combined resources of the Hubble Space Telescope and the new Atacama Large Millimeter/submillimeter Array (ALMA) in Chile's Atacama Desert. The data collected through these observations answered the initial question about the source of energy powering Himiko, but revealed some puzzling data as well.

The Hubble images, receiving optical and ultraviolet light, reveal three stellar clumps covering a space of 20,000 light-years. Each clump is the size of a typical luminous galaxy dating to the epoch of Himiko. Together, the clumps achieve a prodigious rate of star formation, equivalent to about one hundred solar masses per year. This is more than sufficient to explain the existence of Himiko and its gaseous halo. The observation of the three stellar clumps is exciting in itself, as it means that Himiko is a "triple merger," which, according to Ellis, is "a remarkably rare event."

But a surprising anomaly emerged when Himiko was observed by ALMA. Although the giant gas cloud was bustling with energy at ultraviolet and optical frequencies, it was comparatively sleepy in the submillimeter and radio ranges that ALMA detects. Ordinarily, intense star formation creates dust clouds that are composed of elements such as carbon, oxygen, and silicon, which are heavy in comparison to the hydrogen and helium of the early universe. When these dust clouds are heated up by the ultraviolet light emitted by the developing stars, the dust reradiates the ultraviolet light out into the universe at radio wavelengths. But ALMA did not receive significant radio signals from Himiko, suggesting that heavier elements are not present. Also missing was the spectral signature associated with the emission of gaseous carbon, something also common in galaxies with intense star formation.

Both of these nondetections—of substantial radio waves and of gaseous carbon—are perplexing since carbon is ordinarily rapidly synthesized in young stars. Indeed, carbon emission has heretofore been recommended as a tracer of star formation in distant galaxies. But, as Ellis and his fellow astronomers found, Himiko does not contain the dust clouds of heavier elements that astronomers find in typical energetic galaxies. Instead its interstellar gas is composed of hydrogen and helium—primitive materials formed in the Big Bang itself.

Ellis and his fellow astronomers did not come to this conclusion quickly. They first carefully ruled out several other possible explanations for Himiko, including that the giant blob is being created by the magnification of a foreground object by a phenomenon known as gravitational lensing, or is being powered by a massive black hole at its center. Ultimately, the team concluded that Himiko is most likely a primordial galaxy caught in the moment of its formation between 400 million to 1 billion years after the Big Bang, a period astronomers term the cosmic dawn.

"Astronomers are usually excited when a signal from an object is detected," Ellis says, "but in this case it's the absence of a signal from heavy elements that is the most exciting result!"

The paper reporting the results of this research, titled "An Intensely Star-Forming Galaxy at Z ~ 7 with Low Dust and Metal Content Revealed by Deep ALMA and HST Observations," will be published in the December 1, 2013, issue of the Astrophysical Journal. The work was funded by NASA through a grant from the Space Telescope Science Institute, the World Premier International Research Center Initiative (WPI Initiative), and the Japan Society for the Promotion of Science (JSPS).

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Cynthia Eller
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A Mathematical Approach to Physical Problems: An Interview with Rupert Frank

Rupert Frank joined the Caltech faculty this spring as a professor of mathematics. Originally from Munich, Germany, Frank graduated from the Ludwig Maximilian University in his hometown in 2003 and his PhD from the Royal Institute of Technology in Stockholm, Sweden, in 2007. After completing a postdoctoral position at Princeton University, he was hired as an instructor there and quickly worked his way up to assistant professor. Frank recently answered a few questions about his work at the intersection of mathematics and physics.

What do you work on?

I work in this area called mathematical physics. It involves taking things that we see and observe in nature and trying to explain them mathematically from first principles. In mathematics, people often say that they're doing algebra or geometry or something, where they are talking about the methods they are using. However, for us it's more that we use whatever methods we need in order to understand a concrete problem. It's much more problem-specific.

For example, one thing that we still cannot explain—that we are actually really far from being able to explain—is the emergence of periodic structures; that is, structures that repeat themselves. It's clear in nature that it does happen. We see crystals, for example. But we still have no idea why this happens. It's embarrassing really.

So how do you approach a problem like that?

We like to start, for example, with the rules of quantum mechanics—some axioms, which describe the state and the energy of a system. From there, we would like to see that periodic structures can emerge on a macroscopic scale.

Sometimes we work with smaller dimensions—one-dimensional or two-dimensional models, not three dimensional, as nature is. Or we work with discrete models where you assume that all objects can only sit at discrete sites; they cannot move continuously through space. There is a hope that by working with such models, one can reveal more about the overall system.

What problems are you currently addressing?

An important aspect of my work is symmetry and symmetry breaking. Periodicity is a particular case of symmetry.

A problem that I'm always working on is how to explain superconductivity. Superconductivity is a quantum phenomenon that happens on a macroscopic scale, meaning that I can observe it with my bare eyes. [The phenomenon involves the electrical resistance of certain metals and ceramics dropping to zero when cooled below a particular critical temperature. This means such materials can conduct electricity for longer periods, more efficiently. They also repel magnetic fields.] But I cannot explain it with ordinary classical mechanics; I need quantum mechanics. So again, the point is how do we come up with a theory for superconductivity on a macroscopic scale from a microscopic model using the laws of quantum mechanics? And that has been understood, I would say, on a physical level, and there are models that work numerically very well, but mathematically it has not been clarified.

How would you say the discipline of mathematical physics informs both mathematics and physics?

Well, mathematics and physics have always been interrelated, and a lot of mathematics has been developed while trying to solve physical problems. I think physics, from a mathematics perspective, leads to interesting mathematical problems. You are trying to prove something, and it's typically related to some optimization problem—where you want to minimize energy costs or something. So it gives you a way of thinking.

In terms of the benefit to physics, I think we can sometimes provide a different perspective. Physicists typically speak about what they consider to be typical cases within a model, whereas in mathematics, one usually works on the negative side—trying to exclude the atypical. So from time to time, we come up with problems that really require physical explanation that has not been there before.

How did you originally become interested in mathematics and physics?

Actually, both my mother and my father are mathematicians, and one of my brothers is a mathematician; the other is a computer scientist. So it was around when I was growing up, that's for sure. By my third year of university studies, I knew which field of mathematics I wanted to focus on. It can be called functional analysis, operator theory, or mathematical physics. And I saw that all of this was intrinsically related to quantum mechanics. To a certain extent, this field of mathematics was created to explain quantum mechanics. So it was clear that I had to go into physics.

Why did you decide to come to Caltech?

Well, it's a very nice place, and it's a smaller place. That gives you a lot of opportunities because you're not only one of the many. Everybody expects you to do something, and they help you to do it. That's something that I really appreciate.

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Kimm Fesenmaier
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Interactions in Space: An Interview with Philip Hopkins

Philip Hopkins, Caltech's newest assistant professor of theoretical astrophysics, describes his work as studying the formation of really big things—like stars, galaxies, black holes, and planets. Although these "big things" may seem wildly different from one another, Hopkins creates models of these events that focus on the interconnectedness of the universe—such as how the formation of a single star can have an impact on the galaxy as a whole.

Originally from Cleveland, Hopkins received his bachelor's in astronomy from Princeton in 2004 and his doctorate from Harvard in 2008. After completing several postdoctoral fellowships at UC Berkeley, Hopkins joined the Caltech faculty in September 2013. Recently, he sat down with us to talk about his work.

Why are you excited to be at Caltech?

It's a fantastic astronomy department. And although there really aren't any other theorists here who do the same kind of work that I do, a good portion of the department is working on the observational side of the things I'm working on. That's super exciting to me, because I feel like now I'm in the heart of where all the observations are coming from. It also helps that my wife got a job next door at IPAC [the Infrared Processing and Analysis Center]. She's an astronomer, too—a planet hunter.

Can you tell us a little bit about your research?

I work on a broad range of topics, but basically I like studying how big things form. I study how galaxies form, how stars form, and how supermassive black holes form. Recently, I started studying how planets form. When you study the formation of entire galaxies and the formation of single planets, it's really a wide range of scales, but a lot of those problems involve the same basic physics—gravity and fluid dynamics—just on larger scales and smaller scales. Right now, I'm mostly focused on how the formation of stars, galaxies, planets, and black holes feed back on one another. The big realization in the past few years in almost all of those fields has been that you can't cleanly separate these big events. You can't say, "My research is focused on galaxies, so I don't have to care about individual stars."

We're trying to study the interplay in detail. We want to see if you can put these interactions in a model, where you start in the very early universe and try to evolve everything through to today.

For example, a star exploding as a supernova has a big impact back on the entire galaxy, and then that, in turn, changes how the next generation of stars, black holes, and planets form. There is some kind of constant feedback loop between all of these processes. We study a lot of those interactions, and in our study, there is a lot of crossing between different fields of astronomy. I think it's a good time to be doing this interdisciplinary work because those fields have been separated for a long time.

What is your relationship with the observers on campus?

It's a lot of back and forth—so it's a little feedback loop of its own. They want to know what they can do with their data, and they want to be able to test models, so sometimes I go to them and I say, "I have this model. Here are the predictions it makes." And sometimes they come to me, and they say, "We saw this weird thing. Do you have an explanation, or can you think of one?" Those are the most exciting: when something is unanticipated, and you get a whole new project out of trying to figure out what's going on.

These are always messy problems because there is always a huge range of possible models out there. I think the observers on campus are looking forward to having a theorist there to help them decide how they can really discriminate between the different models and what properties we need to measure.

Is there anyone in particular that you're looking forward to working with?

In the past, I've worked with Richard Ellis and Chuck Steidel—both do observations of galaxies in the very early universe—and many observers at IPAC and JPL. I'm also thinking about other possible collaborations, but it's still early; I've only been here a few weeks.

How did you get started in this field?

My parents are an art history major and a sociology major who never took a math or science class after junior year of high school, so they don't know quite what happened with me. I always liked science, but I also really liked any subject that was removed from reality. I feel like biology was too practical to me. When I went to college, I started taking courses to be a physics major. I had read a lot of books on string theory, and I thought that was cool. But then I had the "good fortune" to have a terrible adviser for my first physics project who basically convinced me that I didn't want to do physics anymore. I was about to switch to becoming a classics major when my roommate convinced me to take an astronomy class. I didn't even have the requirements for the class, but the professor said it was fine, so I took it, and I loved it. And then I took the second one. When I look back on my first experiences in physics and my first experiences in astronomy, it is like night and day.

What's most exciting in your research right now?

There's so much happening that's new. Observations are just pouring in—new planets are being discovered, and new galaxies are being discovered at farther and farther distances and earlier times—and the theory is way behind the observations. So, I'm constantly asking if we are even in the right ballpark. Are we qualitatively near some explanation that actually works for all of this? It's exciting. Unlike in a lot of fields, there's so much new data that a single person can write an interesting paper or make an interesting measurement in just a few months. That's definitely something that's not true in a lot of the sciences. 

Is there a certain research question that keeps you up at night?

The boring answer is: "Where is the newest bug in my simulations?"
For all the romance of looking into the skies, the truth is that I spend most of my day sitting at a computer, debugging code. These big simulations have a couple hundred thousand lines of code that you have to worry about, so it's quite a process.

Does the type of work that you are doing carry over to other fields?

I think it does and not always in the ways I would expect it to. Some of the things I've been working on recently are really more about fluid dynamics. For example, if you think about the gas in galaxies and the gas that forms stars, turbulence is really important. Turbulence is a problem in a whole range of fields—and it turns out there are some interesting problems in turbulence that the astrophysicists have really highlighted.

Surprisingly, I've also found myself talking to people who create models of smog formation. My research involves the dust grains inside of the disks in which planets form and how the dust grains get concentrated in certain regions after swirling around in little turbulent vortices. Although this is a very new topic in astrophysics, there is a whole field studying the phenomenon in smokestacks. The two fields are addressing different problems, but we're sort of converging on the same place from our different sides.

Do you have any interests outside of astronomy?

I really like skiing, and I'm also a big movie nerd. As for a genre, my highbrow answer is that I enjoy film noir; my lowbrow answer is that I'm a big fan of stupid action movies. I will get into long discussions about why Die Hard is the greatest movie ever made.

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John H. Schwarz Wins Physics Frontiers Prize

John H. Schwarz, the Harold Brown Professor of Theoretical Physics at Caltech, and Michael B. Green of the University of Cambridge have been awarded one of three 2014 Physics Frontiers Prizes in recognition of the new perspectives they have brought to quantum gravity and the unification of the fundamental physical forces of the universe. Each Physics Frontiers Prize comes with a $300,000 award and eligibility for the 2014 Fundamental Physics Prize, which, at $3 million, is one of the largest academic prizes in the world.

The Physics Frontiers Prize is awarded each year by the Fundamental Physics Prize Foundation, which was established in July 2012 by Russian physicist and Internet entrepreneur Yuri Milner to recognize groundbreaking work in the field. Previous winners include Caltech's Alexei Kitaev, Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics. He and the other laureates—including theoretical physicist Stephen Hawking—served on the selection committee for this year's prize.

Schwarz and Green were honored for developing superstring theory during their collaboration between 1979 and 1986. Its predecessor, string theory, originated in the late 1960s in response to the rapid discovery of many new particles via accelerator experiments. Theoretical physicists, says Schwarz, tried "to make order out of all this chaos" by postulating that the fundamental object of the universe is the string and that the various particles in the universe could be adequately described as different oscillation modes of the string. It was thought for a time that string theory would yield an explanation of the strong nuclear force that binds protons and neutrons together in an atom's nucleus (or even more fundamentally, the quarks and gluons that make up protons and neutrons). But then in the mid-1970s, quantum chromodynamics provided an excellent account of the strong nuclear force, and string theory fell out of favor among most theoretical physicists.

In 1974, Schwarz and his then collaborator, Joel Scherk, suggested a different possible use of string theory, and it was the granddaddy of them all, at least in the terms of modern physics: a quantum theory of gravity and the unification of all the forces in nature. To follow up on this suggestion, Schwarz began his collaboration with Green in 1979, and together they created superstring theory, a version of string theory that relies on the property of supersymmetry to relate the two fundamental types of particles in quantum theory—bosons and fermions—to one another.

According to Schwarz, this is "a very ambitious project, and not something that's going to be completed in my lifetime." But, he says, "people are making lots and lots of progress. We keep discovering new things about superstring theory, which give us the sense that we're closing in on something really important." Indeed, experimental physicists working on CERN's Large Hadron Collider may soon be able to prove the existence of supersymmetry, which, says Schwarz, "wouldn't prove that superstring theory is right, but would be extremely encouraging."

This feeling of the impending success of superstring theory has not always been shared throughout the scientific community. When Schwarz and Green began their work together in 1979, it was, says Schwarz, "not particularly fashionable or popular." But in 1984, the pair's discovery of the so-called Green-Schwarz anomaly cancellation mechanism brought new excitement to superstring theory. "It has remained popular ever since—30 years later," Schwarz remarks.

Tom Soifer, chair of Caltech's Division of Physics, Mathematics and Astronomy, says he is delighted that the Fundamental Physics Prize Foundation chose Schwarz and Green for this honor, noting that while they were developing superstring theory, "these two were in the wilderness. But at Caltech," says Soifer, "we support these solo quests and see them through to fruition."

Schwarz notes that he is especially honored because "the people who were making the selection were other theoretical physicists who've already won the prize, and they are people that I respect and admire. Being chosen by them is particularly meaningful."

The winner of the $3 million Fundamental Physics Prize for 2014 will be announced on December 12 in San Francisco.

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Cynthia Eller
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From One Collapsing Star, Two Black Holes Form and Fuse

Black holes—massive objects in space with gravitational forces so strong that not even light can escape them—come in a variety of sizes. On the smaller end of the scale are the stellar-mass black holes that are formed during the deaths of stars. At the larger end are supermassive black holes, which contain up to one billion times the mass of our sun. Over billions of years, small black holes can slowly grow into the supermassive variety by taking on mass from their surroundings and also by merging with other black holes. But this slow process can't explain the problem of supermassive black holes existing in the early universe—such black holes would have formed less than one billion years after the Big Bang.

Now new findings by researchers at the California Institute of Technology (Caltech) may help to test a model that solves this problem.

Certain models of supermassive black hole growth invoke the presence of "seed" black holes that result from the deaths of very early stars. These seed black holes gain mass and increase in size by picking up the materials around them—a process called accretion—or by merging with other black holes. "But in these previous models, there was simply not enough time for any black hole to reach a supermassive scale so soon after the birth of the universe," says Christian Reisswig, NASA Einstein Postdoctoral Fellow in Astrophysics at Caltech and the lead author of the study. "The growth of black holes to supermassive scales in the young universe seems only possible if the 'seed' mass of the collapsing object was already sufficiently large," he says.

To investigate the origins of young supermassive black holes, Reisswig, in collaboration with Christian Ott, assistant professor of theoretical astrophysics, and their colleagues turned to a model involving supermassive stars. These giant, rather exotic stars are hypothesized to have existed for just a brief time in the early universe. Unlike ordinary stars, supermassive stars are stabilized against gravity mostly by their own photon radiation. In a very massive star, photon radiation—the outward flux of photons that is generated due to the star's very high interior temperatures—pushes gas from the star outward in opposition to the gravitational force that pulls the gas back in. When the two forces are equal, this balance is called hydrostatic equilibrium.

During its life, a supermassive star slowly cools due to energy loss through the emission of photon radiation. As the star cools, it becomes more compact, and its central density slowly increases. This process lasts for a couple of million years until the star has reached sufficient compactness for gravitational instability to set in and for the star to start collapsing gravitationally, Reisswig says.

Previous studies predicted that when supermassive stars collapse, they maintain a spherical shape that possibly becomes flattened due to rapid rotation. This shape is called an axisymmetric configuration. Incorporating the fact that very rapidly spinning stars are prone to tiny perturbations, Reisswig and his colleagues predicted that these perturbations could cause the stars to deviate into non-axisymmetric shapes during the collapse. Such initially tiny perturbations would grow rapidly, ultimately causing the gas inside the collapsing star to clump and to form high-density fragments.

These fragments would orbit the center of the star and become increasingly dense as they picked up matter during the collapse; they would also increase in temperature. And then, Reisswig says, "an interesting effect kicks in." At sufficiently high temperatures, there would be enough energy available to match up electrons and their antiparticles, or positrons, into what are known as electron-positron pairs. The creation of electron-positron pairs would cause a loss of pressure, further accelerating the collapse; as a result, the two orbiting fragments would ultimately become so dense that a black hole could form at each clump. The pair of black holes might then spiral around one another before merging to become one large black hole. "This is a new finding," Reisswig says. "Nobody has ever predicted that a single collapsing star could produce a pair of black holes that then merge."

Reisswig and his colleagues used supercomputers to simulate a supermassive star that is on the verge of collapse. The simulation was visualized with a video made by combining millions of points representing numerical data about density, gravitational fields, and other properties of the gases that make up the collapsing stars.

Although the study involved computer simulations and is thus purely theoretical, in practice, the formation and merger of pairs of black holes can give rise to tremendously powerful gravitational radiation—ripples in the fabric of space and time, traveling at the speed of light—that is likely to be visible at the edge of our universe, Reisswig says. Ground-based observatories such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), comanaged by Caltech, are searching for signs of this gravitational radiation, which was first predicted by Albert Einstein in his general theory of relativity; future space-borne gravitational-wave observatories, Reisswig says, will be necessary to detect the types of gravitational waves that would confirm these recent findings.

Ott says that these findings will have important implications for cosmology. "The emitted gravitational-wave signal and its potential detection will inform researchers about the formation process of the first supermassive black holes in the still very young universe, and may settle some—and raise new—important questions on the history of our universe," he says.

These findings were published in Physical Review Letters the week of October 11 in a paper titled "Formation and Coalescence of Cosmological Supermassive-Black-Hole Binaries in Supermassive-Star Collapse." Caltech coauthors authors on the study include Ernazar Abdikamalov, Roland Haas, Philipp Mösta. Another coauthor on the study, Erik Schnetter, is at the Perimeter Institute for Theoretical Physics in Canada. The work was funded by the National Science Foundation, NASA, the Alfred P. Sloan Foundation, and the Sherman Fairchild Foundation.

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qCraft Introduces Gaming Kids to Quantum Principles

Finding common ground between schoolchildren and quantum-mechanics researchers is no easy task. After all, understanding quantum mechanics—the physics that governs the behavior of matter and light at the atomic (and subatomic) scale—can be daunting even for some physicists. However, through a recent collaboration with Google, researchers at Caltech have created a new space for this unlikely interaction—in the world of Minecraft, a popular video game.

The project originated five months ago, when Spyridon Michalakis, a staff researcher at Caltech's Institute for Quantum Information and Matter (IQIM), received a phone call from Google Creative Lab executive producer Lorraine Yurshansky. Yurshansky was calling about making a promotional video for Google's recent collaboration with NASA and the Universities Space Research Association on the development of the Quantum Artificial Intelligence Lab. The collaborators hope that the new lab, hosted at NASA Ames Research Center, will harness the power of quantum computing—next-generation computing technologies that are rooted in the principles of quantum mechanics—in order to solve currently intractable problems in machine learning and optimization. During their conversation, Michalakis, who is also the outreach manager at IQIM, brought up educational outreach as a way to invest in the future of quantum computing.

"To me, more important than telling kids and the public what we've accomplished already is to tell them of all of the exciting things that have yet to be discovered but will be discovered—by them. In the end, I think that is the point of educational outreach. It is not just to brag about what we've done in academia or to get research funding," Michalakis explains. "We're trying to get kids excited about the future, and I thought Google's other educational involvement with STEM outreach and the maker movement was a good example of this. "

The technology giant quickly got on board. A few weeks after the initial phone call, Michalakis was approached again by Google Creative Lab, which had a proposal for IQIM: come up with a way to use Minecraft to get kids excited about quantum mechanics and quantum computing.

"At first, I did not know what Minecraft was," recalls Michalakis about his first introduction to the video game. "But then I saw it, and I thought, 'This is huge! It's everywhere!'"

In Minecraft, which has been downloaded more than 30 million times worldwide, players can freely build and create their own world by mining and stacking different types of bricks in a sandbox-like environment. Because of its customizable dynamic, the game has also become a background platform for many user-generated modifications, or "mods," that add novel capabilities, brick textures, and properties to the original Minecraft game.

Partnering with the creators of MinecraftEdu—the educational arm of Minecraft—Michalakis and game developers from E-Line Media developed a new mod, produced and funded by Google, to introduce quantum mechanics into the game's landscape.

The mod, dubbed qCraft, was unveiled for download on October 15. Although the project was completed in just a few months, Michalakis found that striking a balance between quantum learning and a fun gameplay experience was challenging because the general elements of the classic Minecraft game obey the laws of classical mechanics—the rules that govern the behaviors of larger objects, like molecules, grains of sand, and even humans. "I had to think, How do I bring quantum mechanics into the classical world of Minecraft?" Michalakis says. "I struggled with it because I wanted to recreate quantum mechanics as faithfully as possible."

qCraft uses the Minecraft platform to introduce three high-level quantum-mechanical concepts: observational dependency, superposition, and entanglement. The mod informally teaches players about observational dependency by allowing them to create either quantum blocks or "observer dependent blocks" (ODBs)—which are classical, but have some quantum-like behaviors. ODBs, Michalakis says, are like rolled dice: if you roll a six, there are six dots on the top face, and the only way this number "changes" is if you look at the die from the bottom or a side, where you will see a different, but fixed, number. Instead of numbers, boxes in qCraft can have different materials on each face, such as diamond or gold.

Using this first concept as a starting point, players can learn more about the vagaries of the quantum universe and how it differs from the classical one by observing in the quantum blocks a phenomenon known as superposition. Superposition is the principle that allows particles to occupy more than one state at the same time (and that permits Schrödinger's notorious cat to be simultaneously dead and alive). "In quantum objects, things behave differently. If you were to roll a six on a quantum die, the number on the face of the die will still be a six. But if you now look from the side, you will not always see a three where a three was supposed to be—you will sometimes see a three and sometimes a four, and you will never be able to predict which one will show up," Michalakis says. Superposition in qCraft means that one face of a quantum block could be gold at first glance, but after looking at another face and then coming back for a second glance, that same face is just as likely to be diamond as it is to be gold—or to completely disappear.

Additionally, the quantum blocks in one qCraft world can be "entangled" with the blocks in another qCraft world, allowing them to share information and to influence each other, despite having no visible connection. Such entanglement allows a player to make one quantum block disappear—and in the process make a group of quantum wall blocks disappear to create a doorway. Entanglement (which Albert Einstein called "spooky action at a distance") may not be possible in the classical world, but researchers at IQIM and around the world, through their experiments, are trying to scale up the weirdness of the quantum world, pushing the boundaries between our classical intuition and the strange and profound properties of quantum-mechanical objects. It is a herculean effort, Michalakis notes, all the more difficult because of the fragile nature of information at the quantum level, which tends to rapidly "decohere" into its classical counterparts due to interactions with its surrounding environment, the ever-present observer.

To deal with these environmental interactions, a feature of the mod even allows players to wear "quantum goggles" so that they can hide their role as an observer, leaving the fate of the quantum blocks unresolved.

Michalakis will provide more insight into how the behaviors of these modified Minecraft blocks relate to quantum mechanics in a series of blog posts on the qCraft website. "Through the game and the blog posts, we hope to bring the public up to speed on some of the most fascinating physics research that is happening right now, including studies of quantum mechanics, black holes, time travel, wormholes, and more," he says.

The outreach plan for qCraft doesn't end there. In November, Michalakis, along with the qCraft team and the Caltech graduate and undergraduate students who helped him to build and beta-test the mod, will attend Minecon 2013, an annual convention for Minecraft players, developers, and enthusiasts. At the meeting, the team will promote the mod, explain concepts, and answer questions from current qCraft users.

The mod is already gathering a fan base, but Michalakis says the final success will be when players start to dig deeper and begin to learn about the equations and concepts that are its foundation. Indeed, Michalakis hopes that qCraft will encourage many future scientists to "look under the hood" of quantum mechanics. "We're the table upon which they can build something bigger. We're not the end," he says.

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Building the World's Most Sensitive Detectors: A Conversation with Rana Adhikari

Caltech professor of physics Rana Adhikari has been on a singular quest for 15 years: to detect gravitational waves.

Gravitational waves—ripples in the fabric of space-time—are predicted by Einstein's theory of general relativity. Major astrophysical events such as the collapse of a binary system of neutron stars or black holes or one of each should release intense gravitational waves in the frequency range that we potentially might detect here on Earth. As theorized, gravitational waves are curious things; they move across the universe at the speed of light and pass right through everything they encounter without being affected as electromagnetic waves (such as light and radio waves) would be. And yet they are very weak compared to electromagnetic waves.

Scientists began to search for gravitational waves at the end of the 1960s, trying out a variety of technologies, including metal or ceramic bars that were designed to resonate at the proper frequencies when struck by gravitational waves. By the 1990s, the technology of choice was the laser interferometer, an L-shaped apparatus with two vacuum pipes four feet in diameter through which a laser beam passes. The laser's job is to sense the slightest motion in large glass mirrors hung at the far end of each pipe. Today the LIGO (Laser Interferometry Gravitational-Wave Observatory) project, a cooperative venture between Caltech and the Massachusetts Institute of Technology funded by the National Science Foundation, operates two laser interferometers whose vacuum pipes are four kilometers long: one in Livingston, Louisiana, and the other in Hanford, Washington. The detectors are currently offline while Advanced LIGO, slated to begin operation in 2014, is fitted into the apparatus.

So far the number of gravitational waves we have directly observed is zero.

Professor Adhikari, and indeed the entire LIGO team, is devoted to changing that tally in our favor. Adhikari recently sat down to answer a few questions about his work on LIGO and his experience of the students, staff, and faculty at Caltech.

How did you get started with the search for gravitational waves?

Whoever recruits you into this field says, "This is the best time to get in. You're getting in on the ground floor! The past has been a hard slog, but this is the perfect moment. In the next couple of years, boom! It's all going to play out." I heard that and thought, "Oh yes, I believe you. This is a great deal for me."

Now I say the same thing to potential recruits, but now it's true!

How do you feel about the fact that gravitational waves still haven't been detected?

It can be frustrating. Other astronomers have it a lot easier. Every time they point an instrument at the sky, they detect something. Meanwhile, LIGO has been waiting decades for anything, just one little blip. I went to an astronomy conference in San Francisco a while ago, and I swear, every single person who got up to give a talk said, "For six months we worked on this machine, and then we put it in a remote place in Africa or Chile, and as soon as we did, we saw this pulsar and this explosion. It was wonderful!" When I got up to give my talk, I pounded on the podium for a while and said, "What about me? I've been working on this thing for 15 years, and I've got nothing. Where's my signal?" People came up afterward and patted me on the back and said, "It's all right, it's going to happen for you too, don't worry."

Do you think you will eventually detect gravitational waves?

Yes, if our device is as sensitive as we believe it is, and if the kind of dramatic events that produce significant gravitational waves happen often enough.

I have extremely high confidence that these events are happening. In 1974, two radio astronomers, Russell Hulse and Joe Taylor, then at the University of Massachusetts at Amherst, observed a binary neutron-star system from a radio observatory in Puerto Rico. They and others have been tracking it ever since. The orbit of the stars is gradually decaying, which indicates the presence of gravitation. But more importantly, the decay is exactly as predicted by Einstein's theory. And we know that there are other events like this that would produce gravitational waves. People observe some such events using radio astronomy and optical astronomy. What we don't know is precisely how often they happen.

And you believe that if they happen, LIGO will detect them?

I think the main reason we stick with this effort is because our detectors are working like they should be. We can see a big piece of glass—a 40-kilogram mirror—move back and forth a distance equivalent to one-billionth the size of a hydrogen atom in response to a gravitational wave. You might say it could move by the size of a hydrogen atom and be believed. But one-billionth? Come on. It seems like this level of sensitivity can't be possible. When you tell people how sensitive LIGO is, it sounds like you're a nutcase—but we've measured it to be that precise.

With an instrument that sensitive, how do you avoid measuring everything else?

LIGO reacts to everything. If there's a lightning strike in Kansas, we see a magnetic pulse; if there's an earthquake anywhere in the world, our detector shakes around. Once, we had interference in our signal at the LIGO site in eastern Washington, and it was due to the release of a little extra water by a dam in western Washington.

Our whole concept is to get a thousand different kinds of sensors attached to LIGO: accelerometers, magnetometers, microphones, pressure sensors, devices to measure temperature, cosmic rays, everything. Our detector is the only thing in the world that will ever sense a gravitational wave, because it is so hard to detect. So if you see a blip in any other sensor, you're seeing something other than a gravitational wave.

Are you working to further increase the sensitivity?

All the time. For example, we originally decided to go with glass—fused silica—as the material for the mirrors. People have been studying glass for hundreds of years; it has some almost magical properties that may help LIGO to detect gravitational waves.

More recently we've learned that there may be an even quieter material: silicon crystal. Silicon has some difficult properties, but they vanish at about 120 degrees Kelvin, or about minus 150 degrees centigrade. So now we are looking at developing silicon detectors and keeping them in a cryogenic atmosphere. Unfortunately, this means completely revamping LIGO. So while the next generation of LIGO—Advanced LIGO—is online, we will already be working on its successor.

How are students involved in your work on LIGO?

From the beginning, I thought that if we were going to make LIGO work, we had better get a huge gang of students from Caltech working on this project. That's what makes it all go. My students work from . . . well, sometime after lunch until the sun rises. Starting several years ago, we set students to work on prototyping new, speculative ideas for LIGO. Some of these ideas never add up to anything, but others that we originally thought wouldn't be of any use at all are now the standard vanilla technology of LIGO. We ask ourselves, "How did we ever live without this?"

One of these student projects was to imagine putting a bunch of microphones and vibration sensors around LIGO. Then, without trying to determine which events were creating which reactions, we simply inputted the signals into a computer and told it to subtract the noise out of the interferometer. We found out that there were already learning algorithms like this created by people for other reasons. In fact, to get rid of all kinds of noise in the interferometer we now use similar learning algorithms to those used in noise-canceling headphones.

We have international collaborators in Japan, Italy, France, Germany, Australia, and India, so we always have undergraduate and graduate students coming from these places. Our labs are an international mix of people of different ages and levels. And everyone is really into the project. I don't have to do any cheerleading; they're already self-motivated.

What excites you about Caltech?

Getting to work with the people here. They're all really bright and energetic and thinking about things all the time. Before physics, I had several other jobs, and mostly we tried to figure out how to do the least possible amount of work until five o'clock came around and we could get out. Here the work is so exciting that you can easily lose track of time and leave six hours late.

Caltech is a special place because of its intensity, and also because of all the expertise that is around. We have geophysics, aeronautics, applied physics . . . And the teaching is wonderful. For the past three years I have taught electromagnetism to nonphysics majors. It's full of practical questions like "What is this thing?" I learn a lot from teaching that.

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Cynthia Eller
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Tuesday, December 10, 2013
Noyes 153 (J. Holmes Sturdivant Lecture Hall)

Advice for Future New Faculty: Caltech Postdoc Association Event

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