Caltech Rocket Experiment Finds Surprising Cosmic Light

Using an experiment carried into space on a NASA suborbital rocket, astronomers at Caltech and their colleagues have detected a diffuse cosmic glow that appears to represent more light than that produced by known galaxies in the universe.

The researchers, including Caltech Professor of Physics Jamie Bock and Caltech Senior Postdoctoral Fellow Michael Zemcov, say that the best explanation is that the cosmic light—described in a paper published November 7 in the journal Science—originates from stars that were stripped away from their parent galaxies and flung out into space as those galaxies collided and merged with other galaxies.

The discovery suggests that many such previously undetected stars permeate what had been thought to be dark spaces between galaxies, forming an interconnected sea of stars. "Measuring such large fluctuations surprised us, but we carried out many tests to show the results are reliable," says Zemcov, who led the study.

Although they cannot be seen individually, "the total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies," says Bock, also a senior research scientist at JPL. Bock is the principal investigator of the rocket project, called the Cosmic Infrared Background Experiment, or CIBER, which originated at Caltech and flew on four rocket flights from 2009 through 2013.

In earlier studies, NASA's Spitzer Space Telescope, which sees the universe at longer wavelengths, had observed a splotchy pattern of infrared light called the cosmic infrared background. The splotches are much bigger than individual galaxies. "We are measuring structures that are grand on a cosmic scale," says Zemcov, "and these sizes are associated with galaxies bunching together on a large-scale pattern." Initially some researchers proposed that this light came from the very first galaxies to form and ignite stars after the Big Bang. Others, however, have argued the light originated from stars stripped from galaxies in more recent times.

CIBER was designed to help settle the debate. "CIBER was born as a conversation with Asantha Cooray, a theoretical cosmologist at UC Irvine and at the time a postdoc at Caltech with [former professor] Marc Kamionkowski," Bock explains. "Asantha developed an idea for studying galaxies by measuring their large-scale structure. Galaxies form in dark-matter halos, which are over-dense regions initially seeded in the early universe by inflation. Furthermore, galaxies not only start out in these halos, they tend to cluster together as well. Asantha had the brilliant idea to measure this large-scale structure directly from maps. Experimentally, it is much easier for us to make a map by taking a wide-field picture with a small camera, than going through and measuring faint galaxies one by one with a large telescope." 

Cooray originally developed this approach for the longer infrared wavelengths observed by the European Space Agency's Herschel Space Observatory. "With its 3.5-meter diameter mirror, Herschel is too small to count up all the galaxies that make the infrared background light, so he instead obtained this information from the spatial structure in the map," Bock says. 

"Meanwhile, I had been working on near-infrared rocket experiments, and was interested in new ways to use this unique idea to study the extragalactic background," he says. The extragalactic infrared background represents all of the infrared light from all of the sources in the universe, "and there were some hints we didn't know where it was all coming from."

In other words, if you calculate the light produced by individual galaxies, you would find they made less than the background light. "One could try and measure the total sky brightness directly," Bock says, "but the problem is that the foreground 'Zodiacal light,' due to dust in the solar system reflecting light from the sun, is so bright that it is hard to subtract with enough accuracy to measure the extragalactic background. So we put these two ideas together, applying Asantha's mapping approach to new wavelengths, and decided that the best way to get at the extragalactic background was to measure spatial fluctuations on angular scales around a degree. That led to CIBER."

The CIBER experiment consists of three instruments, including two spectrometers to determine the brightness of Zodiacal light and measure the cosmic infrared background directly. The measurements in the recent publication are made with two wide-field cameras to search for fluctuations in two wavelengths of near infrared light. Earth's upper atmosphere glows brightly at the CIBER wavelengths. But the measurements can be done in space—avoiding that glow—in just the short amount of time that a suborbital rocket flies above the atmosphere, before descending again back toward the planet.

CIBER flew four missions in all; the paper includes results from the second and third of CIBER's flights, launched in 2010 and 2012 from White Sands Missile Range in New Mexico and recovered afterward by parachute. In the flights, the researchers observed the same part of the sky at a different time of year, and swapped the detector arrays as a crosscheck against data artifacts created by the sensors. "This series of flights was quite helpful in developing complete confidence in the results," says Zemcov. "For the final flight, we decided to get more time above the atmosphere and went with a non-recovered flight into the Atlantic Ocean on a four-stage rocket." (The data from the fourth flight will be discussed in a future paper.)

Based on data from these two launches, the researchers found fluctuations, but they had to go through a careful process to identify and remove local sources, such as the instrument, as well as emissions from the solar system, stars, scattered starlight in the Milky Way, and known galaxies. What is left behind is a splotchy pattern representing fluctuations in the remaining infrared background light. Comparing data from multiple rocket launches, they saw the identical signal. That signal also is observed by comparing CIBER and Spitzer images of the same region of sky. Finally, the team measured the color of the fluctuations by comparing the CIBER results to Spitzer measurements at longer wavelengths. The result is a spectrum with a very blue color, brightest in the CIBER bands.

"CIBER tells us a couple key facts," Zemcov explains. "The fluctuations seem to be too bright to be coming from the first galaxies. You have to burn a large quantity of hydrogen into helium to get that much light, then you have to hide the evidence, because we don't see enough heavy elements made by stellar nucleosynthesis"—the process, occurring within stars, by which heavier elements are created from the fusion of lighter ones—"which means these elements would have to disappear into black holes." 

"The color is also too blue," he says. "First galaxies should appear redder due to their light being absorbed by hydrogen, and we do not see any evidence for such an absorption feature."

In short, Zemcov says, "although we designed our experiment to search for emission from first stars and galaxies, that explanation doesn't fit our data very well. The best interpretation is that we are seeing light from stars outside of galaxies but in the same dark matter halos. The stars have been stripped from their parent galaxies by gravitational interactions—which we know happens from images of interacting galaxies—and flung out to large distances."

The model, Bock admits, "isn't perfect. In fact, the color still isn't quite blue enough to match the data. But even so, the brightness of the fluctuations implies this signal is important in a cosmological sense, as we are tracing a large amount of cosmic light production." 

Future experiments could test whether stray stars are indeed the source of the infrared cosmic glow, the researchers say. If the stars were tossed out from their parent galaxies, they should still be located in the same vicinity. The CIBER team is working on better measurements using more infrared colors to learn how the stripping of stars happened over cosmic history.

In addition to Bock, Zemcov, and Cooray, other coauthors of the paper, "On the Origin of Near-Infrared Extragalactic Background Light Anisotropy," are Joseph Smidt of Los Alamos National Laboratory; Toshiaki Arai, Toshio Matsumoto, Shuji Matsuura, and Takehiko Wada of the Japan Aerospace Exploration Agency; Yan Gong of UC Irvine; Min Gyu Kim of Seoul National University; Phillip Korngut, a postdoctoral scholar at Caltech; Anson Lam of UCLA; Dae Hee Lee and Uk Won Nam of the Korea Astronomy and Space Science Institute (KASI); Gael Roudier of JPL; and Kohji Tsumura of Tohoku University. The work was supported by NASA, with initial support provided by JPL's Director's Research and Development Fund. Japanese participation in CIBER was supported by the Japan Society for the Promotion of Science and the Ministry of Education, Culture, Sports, Science and Technology. Korean participation in CIBER was supported by KASI. 

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No Galaxy Too Small: An Interview with Evan Kirby

Assistant Professor of Astronomy Evan Kirby arrived on campus in August. Born and raised in New Orleans, Kirby earned his BS in 2004 from Stanford University; his undergraduate thesis involved trips to Pasadena to test an instrument built by JPL's Jamie Bock, now also a Caltech professor of physics, and the late Andrew Lange, the Marvin L. Goldberger Professor of Physics at Caltech. Kirby earned his MS and PhD degrees from UC Santa Cruz in 2006 and 2009.  His PhD thesis involved an analysis of the spectra of bright stars in dwarf galaxies orbiting the Milky Way. Then as a Caltech postdoc and Hubble Fellow from 2009 to 2012, he moved on to more distant stars in Andromeda and its satellite galaxies. As a Center for Galaxy Evolution Fellow at UC Irvine from 2012 to 2014, he shifted the focus of his spectral analyses from chemical makeups to stellar motions.


Q: What do you do?

A: I study the smallest galaxies we know about. The Milky Way and our nearest big neighbor galaxy, Andromeda, have pantheons of little galaxies in orbit around them. These galaxies are interesting because they are part of our cosmic story. The first galaxies to form were small ones, and over time they got smashed together to build up bigger ones. Tidal disruptions from our galaxy's gravity will eventually rip apart all the remaining dwarf galaxies orbiting us, and they will dissolve into the Milky Way—stars, dust, gas, and all. Similarly, Andromeda will swallow up its dwarfs.

Both sets of satellite galaxies are close enough that I can see each one's individual stars, instead of seeing the whole galaxy as a little smudge. This is important because I can record the spectrum of each bright star separately. A star's spectrum tells me its composition—how much iron is in that star, how much magnesium, how much calcium, and so on—and by compiling that information for each galaxy I can reconstruct its entire history.

The dwarf galaxies' histories tell us about our own; our galaxy formed at the same time and from the same material. It just got bigger faster.


Q: How big a telescope do you need to see a dwarf galaxy?

A: If you're in the southern hemisphere you can see the Milky Way's two biggest dwarfs, the Large and Small Magellanic Clouds, just by looking up at night. But the third biggest, the Sagittarius Dwarf Elliptical Galaxy, was only discovered in 1994 by a team of astronomers at the Cambridge (UK) Astronomical Survey Unit using a 47½-inch telescope modeled after our own 48-inch Samuel Oschin Telescope at Palomar Observatory. The other dwarf galaxies are a lot smaller and a lot fainter, so you need even bigger telescopes to find them.

However, the 10-meter Keck Telescope on Mauna Kea is definitely my instrument of choice. Andromeda is about 2.5 million light-years away, and the Keck gets me out to about 4.5 million light-years. If I go much beyond Andromeda, I no longer see galaxies as individual stars. And if I turn a medium-sized telescope on Andromeda, the stars become too faint to take spectra.


Q: A galaxy named Segue 2 features prominently on your website. What's the story there?

A: Segue 2 was discovered in 2007 by a group of astronomers at the Institute of Astronomy at Cambridge. I took spectra of many of its stars, which told me how fast they were moving. And I found that Segue 2's velocity dispersion, which is a measure of its mass, was less than 2.2 kilometers per second. That's very, very small, and it implies that Segue 2 has about a thousand stars, and up to another few hundred thousand solar masses' worth of dark matter. By comparison, the Milky Way's velocity dispersion is 200 kilometers per second and its total mass, including dark matter, is somewhere around a trillion solar masses. The Large Magellanic Cloud's mass is 20 times less than that. And the smaller dwarf galaxies typically have a few tens of millions of solar masses. A few hundred thousand solar masses is tiny.


Q: You mentioned dark matter. Does your work tell us anything about the nature of dark matter itself?

A: Absolutely. The currently accepted paradigm is "cold dark matter." Back in the 1980s, theorists began making computer models of the early universe to see how clouds of cold dark matter would coalesce. The big clumps became galaxies like Andromeda and the Milky Way, and the smaller clumps, called subhaloes, became their satellites. The simulations predicted that the Milky Way should be surrounded by lots and lots of satellites having about one one-hundredth the mass of the Magellanic Clouds, and a big problem arose well over a decade ago when we couldn't see as many of them as we thought we should. Finding things like Segue 2 is helping to resolve the missing-satellite problem.

Things got worse about three years ago, when astronomers discovered that not only were a lot of the little satellites missing, a lot of the big satellites are also missing! My officemate at UC Irvine, who did a lot of work on this, calls it the "too-big-to-fail" problem. The cold dark matter theory predicts there should be a decent number of subhaloes about one-tenth the size of the Magellanic Clouds. That's too big to not form stars, and if a subhalo that big forms stars, we should see the resulting galaxies—all of them. But we've counted up all the ones we can see, and we're missing about 10 of them. Either they don't exist, or somehow they did fail to form stars. Both alternatives challenge our understanding of how these dwarf galaxies form.


Q: How did you get started on all this?

A: When I was a little kid, I always wanted to be an astronaut. I realized that was unrealistic, so I chose a slightly less unrealistic goal—to be an astronomer. I subscribed to Astronomy magazine and bought all these astrophysics textbooks. I didn't understand a word of them, but I thought I was so cool for reading them. I went to Stanford knowing that I wanted to study physics and astronomy. I thought I would be a theoretician, but then I realized that observing is way cooler. Going out to the telescope is far more romantic than sitting in front of the computer, and I discovered I loved working with my hands and building instruments.


Q: What do you do for fun?

A: I'm into road cycling. UC Santa Cruz was Mecca for that. I biked uphill to campus four miles every day, and it really got me in shape. It was efficient—you should exercise for half an hour every day, so instead of spending 30 minutes sitting on a bus, I spent 30 minutes sitting on a bicycle.

When I was a Hubble fellow here, I met a postdoc named Hai Fu who became my best friend. I told him I was into biking and he said, "I am too. Let's go on a ride—I know an easy one." So I got in his car that weekend, and he started driving east on 210. After about an hour, I asked, "Where are you taking me?" "Oh, I'm just going to Mount Baldy." Cycling up Mount Baldy, the highest peak in the San Gabriel Mountains, was his idea of an easy ride.

I also play the clarinet. I was pretty serious about it at one point, but never professionally serious. Science and music are both hard to get jobs in, and I knew I had a much better chance in science.

Douglas Smith
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A Newborn Supernova Every Night

Thanks to a $9 million grant from the National Science Foundation and matching funds from the Zwicky Transient Facility (ZTF) collaboration, a new camera is being built at Caltech's Palomar Observatory that will be able to survey the entire Northern Hemisphere sky in a single night, searching for supernovas, black holes, near-Earth asteroids, and other objects. The digital camera will be mounted on the Samuel Oschin Telescope, a wide-field Schmidt telescope that began its first all-sky survey in 1949. That survey, done on glass plates, took nearly a decade to complete.

The ZTF camera's field of view will encompass 47 square degrees, larger than 200 full moons. By contrast, the field of view of the Hubble Space Telescope is so small that a mosaic of 130 of its images of the moon would be needed to see it in its entirety. "The Hubble Space Telescope and the big ground-based telescopes see really deep but have small fields of view," says astrophysicist Eric Bellm, a postdoctoral scholar at Caltech and ZTF's project scientist. With its field of view, ZTF will be able to identify supernovas less than 24 hours old every single night. This quick response is critical, as the light emitted in the first few hours after a supernova explodes contains a wealth of information that cannot be retrieved later.

"Discovery is only the first step," says Shrinivas Kulkarni, ZTF's principal investigator and Caltech's John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science. "When something unusual is found, we will rapidly respond with some of the world's most powerful telescopes," including the Palomar Observatory's 200-inch Hale.

In time, researchers hope, ZTF itself will be pointed at targets identified by the Laser Interferometer Gravitational-wave Observatory (LIGO), an NSF-funded project run by Caltech and MIT that is searching for gravitational waves. These ripples in the fabric of space and time are predicted to occur when neutron stars, black holes, or other massive objects collide. Currently, LIGO is offline undergoing a technical upgrade to Advanced LIGO, which is slated to begin operations in 2016. If and when Advanced LIGO registers a gravitational wave, it will command ZTF to scan the ribbon of sky from which the signal emanated, searching for any visible change that might mark the point of origin.

ZTF—the successor to the intermediate Palomar Transient Factory (iPTF) survey and its predecessor, the Palomar Transient Factory—is a fully automated wide-field survey that uses the Oschin telescope to collect data that are then sent to the Infrared Processing and Analysis Center (IPAC) on the Caltech campus. At IPAC, software developed for PTF looks for anything that has changed between frames. ZTF will shoot one frame per minute at 18 gigabits per frame—the rough equivalent of watching eight hours of high-definition movies on Netflix every 60 seconds.

"ZTF is really about celestial cinematography," says Mansi Kasliwal (PhD '11), currently a visiting associate in astronomy who will start as an assistant professor of astronomy at Caltech in September 2015. "Our new camera can make a movie of the entire sky. Moving solar-system bodies such as asteroids will just pop out at us, and we'll be able to study catastrophic explosive transients such as supernovas and stars being torn apart by black holes."

"Processing so many images in real time is a huge challenge," says IPAC's executive director, George Helou. "It takes imaginative programming and powerful computers." ZTF will visit every corner of the sky some 900 times over the course of its three-year observing program; IPAC will compile the data into atlases of variable stars, active galactic nuclei, and other astronomically interesting objects.

Part of the NSF grant will fund an annual summer institute, coordinated by Pomona College in Claremont, California, to train students from across the United States in the latest astronomy instrumentation skills, large sky surveys, and data-analysis software.

"These undergraduates will be controlling some of the largest telescopes in the world and getting a taste of the excitement of the scientific process," explains Bryan Penprase, a professor at Pomona College and a co-principal investigator on the project, and the organizer of the summer institute. "The technology is so advanced that discoveries will be common. In just one night, the ZTF can discover hundreds of new sources. It's an incredible thing for a student to be able to say, 'I discovered that thing in the sky that no one else has ever seen before.'"

The Zwicky Transient Facility is named in memory of Caltech astronomer Fritz Zwicky, who pioneered the use of wide-field Schmidt-type telescopes for sky surveys. Zwicky was the prime mover behind the Oschin's construction, using its survey plates to hunt for supernovas—a term that Zwicky and Walter Baade coined in 1931. Zwicky also predicted the existence of neutron stars, dark matter, and gravitational lensing.

ZTF is a public-private partnership supported by the National Science Foundation, Caltech, IPAC, the Weizmann Institute of Science (Israel), the Oskar Klein Centre (Sweden), Humboldt University (Germany), Los Alamos National Laboratory, Lawrence Berkeley National Laboratory, the Jet Propulsion Laboratory, the TANGO consortium (Taiwan), the University of Wisconsin–Milwaukee, and Pomona College. The survey will begin in 2017. 

Douglas Smith
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Remembering Tom Tombrello


Thomas Anthony Tombrello, Caltech's Robert H. Goddard Professor of Physics, passed away on September 23, 2014, at age 78. His studies of nuclear reactions in the 1960s helped show how chemical elements are created.

Tombrello was known on campus as a devoted teacher. "Probably his greatest contribution to Caltech was the identification and mentoring of generations of promising undergraduate physicists," says Steven Koonin (BS '72), Caltech's provost from 1995 to 2004 and now director of the Center for Urban Science and Progress at New York University. "I was among the first of those."

"Tom was incredibly enthusiastic, supportive, and generous with his time with my cohort of undergrads, and he kept this up for the next 40 years," says Joe Polchinski (BS '75), a string theorist at the Kavli Institute for Theoretical Physics at UC Santa Barbara.

"Tom counseled me in all aspects of graduate student life—from classes and instructors to the more personal challenges that students face," says France Córdova (PhD '79), the director of the National Science Foundation. "He remained a lifelong friend and counselor. I was buoyed by his email messages, such as the one that followed the announcement of my current position: 'These will be trying times, but you are up to the challenge. If there is any way I can be of help, please let me know.' This was characteristic of his ready support."

Tombrello was born in Austin, Texas, on September 20, 1936. He attended Rice Institute (now Rice University), earning his BA, MA, and PhD in physics in 1958, 1960, and 1961, respectively, before coming to Caltech as a postdoctoral fellow in 1961. He accepted an assistant professorship at Yale in 1963, but returned to Caltech a year later and resumed his research with William Fowler (PhD '36) in the W. K. Kellogg Radiation Laboratory. Fowler and his colleagues had predicted that certain isotopes of lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine would be produced as sun-like stars burned their nuclear fuel. Tombrello synthesized many of these isotopes in Kellogg's megavolt particle accelerator and recorded their spectra, allowing astronomers to measure their stellar abundances and confirm that they appeared in the predicted proportions. He was promoted to assistant professor in 1965, associate professor in 1967, and full professor in 1971.

In 1973, Tombrello took over as principal investigator on the main grant supporting the Kellogg lab, just as money for nuclear physics began to dry up. With some 50 faculty, students, and staff to support, he found other funding by broadening Kellogg's scope of work. He used the particle accelerator to bombard lunar rocks with heavy ions to replicate conditions on the lunar surface and ventured into materials science by conducting radiation-damage studies for the China Lake Naval Weapons Center.

In 1986, Tombrello was put in charge of the physics staffing committee, where he helped hire new physics faculty, according to David Morrisroe Professor of Physics Ed Stone, then the division chair for Physics, Mathematics, and Astronomy.

From 1987 to 1989, Tombrello took a leave of absence from Caltech to become vice president and director of research for Schlumberger-Doll, an oil-industry service company.

Tombrello chaired the Division of Physics, Mathematics and Astronomy from 1998 to 2008. Says Koonin, "I was provost for the majority of that time, and we worked well together, although not without productive tensions. He was an energetic, strategic thinker who advanced the division through hires in quantum optics, string theory, nanotechnology, and space-based X-ray and ultraviolet astronomy." But their "greatest collaborative effort," Koonin says, was the Thirty Meter Telescope, which when completed in the early 2020s, will be the world's most advanced optical and near-infrared observatory.

Tombrello oversaw several other projects during his tenure as division chair. He was deeply involved in the design and construction of the Cahill Center for Astronomy and Astrophysics. He helped establish what is now the Kavli Nanoscience Institute, a nanotechnology fabrication center open to campus and JPL users, and he played an important role in LIGO, the Laser Interferometer Gravitational-wave Observatory.  

Tombrello co-advised many students with nanotechnologist Axel Scherer, the Bernard A. Neches Professor of Electrical Engineering, Applied Physics, and Physics. "Tom was deeply immersed in the work of my group—nanoscale vacuum tubes, new gene-sequencing systems, sensors for oilfield applications, and lithography at the atomic scale," Scherer says. "He had an intuitive understanding of the physics behind the devices."

A self-proclaimed "kindergarten dropout," Tombrello's true calling was teaching. "One of his most important legacies at Caltech was the creation of Physics 11 [in 1989], a freshman physics course that challenged incoming students to think in nonconventional ways," Koonin says. Applicants to the class completed assignments called "hurdles"—questions that had no right answers and generally had little to do with physics. "He wanted to know whether you had the creativity and courage to attack a strange new problem, work on it until you had a solution you believed in, and allow your solution to be judged on its merits," says Phys 11 veteran Charles Tschirhart, class of 2015.

Tombrello recruited faculty mentors for the students admitted to Physics 11; together, the group planned a summer research project for each student. Says Tschirhart, "The class was about as informal as a class can be; we talked about our work while lounging on a circle of beat-up couches around a whiteboard outside Professor Tombrello's office. The professors would sit among us on the couches while we talked. Conversations often strayed to science policy, history, school politics, and general advice for success in science and in life. It was probably the best thing that anyone could have done for my development as a scientist and as a person."

"He was a very kind person to be around," says senior Adam Jermyn. "He understood the undergraduates in a way I think is uncommon among the faculty. He came to our formal dinners, he talked to us outside of class, and he kept his finger on the pulse of student government. When I applied for permission to overload, he said it would make me miserable. However, he let me try it. I was miserable, and I learned a lesson I think he knew I would not have learned if he'd opposed me directly."

"Tom Tombrello was one of Caltech's most dedicated and effective servants," says former Caltech astrophysicist Marc Kamionkowski. "He could be brash, opinionated, and hot-tempered, but he was a deeply devoted and extraordinarily effective PMA chairman. He was not just dutiful and responsible, he was passionate. He believed with every ounce of his being that Caltech was a special place, that its students and faculty were extraordinary, and that it was his mission to do whatever he could to help them out. He worked tirelessly recruiting outstanding faculty and raising money for them while reserving time each week to work with the undergraduates he adored. With his Texas drawl and his frequent references—with a wink of an eye—to his Sicilian origins, he was one of a kind."

"Tom was an ensemble of talents not easily found in one person—a cross between Socrates, Leonardo Da Vinci and Abraham Lincoln," says high-energy physicist Maria Spiropulu, the last faculty member hired while Tombrello was division chair

"For half a century, Tom Tombrello has represented not just the DNA but the heart and soul of Caltech," says author, radio host, and performer Sandra Tsing Loh (BS '83), a Caltech Distinguished Alumna and a Tombrello protégé. "His legacy is legendary. His loss leaves a giant meteorite crater. If heaven has an Ath, Dr. T. is being welcomed to his much-deserved corner table, although we'll sorely miss him from down here."

Tombrello received two teaching awards from the Associated Students of the California Institute of Technology (ASCIT), and, in 1994, the first Richard P. Feynman Prize for Excellence in Teaching, in part for the creation of Physics 11. He was named the William R. Kenan, Jr. Professor of Physics in 1997, and Robert H. Goddard Professor of Physics in 2012. He was also a fellow of the American Physical Society; a member of Sigma Xi, the international honorary society for science and engineering; and of Phi Beta Kappa, the nation's oldest academic honor society.

Tombrello is survived by his second wife, Stephanie; his first wife, Ann, and their children, Christopher Tombrello, Susan Tombrello, and Karen Burgess; and seven grandchildren. He was predeceased by his stepdaughter, Kerstin.

Memorial donations may be made to the Thomas Tombrello Physics 11 Scholarship Fund by clicking on the link to the fund under his picture, selecting "special gifts," scroll downing and checking "other," and writing "Thomas Tombrello Physics 11 Scholarship" in the "Comments" box. 

Plans for a memorial service are pending.

Douglas Smith
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Quantum States of Matter in Crystals

Watson Lecture Preview

David Hsieh, an assistant professor of physics at Caltech, is searching for new forms of matter that exhibit weird quantum properties in bulk. Find out the why, where, and how at 8 p.m. on Wednesday, October 15, in Caltech's Beckman Auditorium. Admission is free.


Q: What do you do?

A: I'm an experimental condensed-matter physicist. I'm searching for quantum phases of matter in crystals big enough to hold in your hand. A quantum phase occurs when the electrons in a crystal share a quantum state that creates an interdependence among them. This can lead to tangible phenomena that seem to defy the laws of everyday physics.  

The three familiar phases of matter—solids, liquids, gases—are governed by electrostatic forces. Likewise, free electrons interact with one another through electrostatic repulsions. If you just threw a bunch of electrons into a box, they'd eventually situate themselves as far away from one another as possible. These forces are not under our control, but when we embed electrons in a crystal, they swim in a lattice of ions that can facilitate many other types of interactions. By properly choosing those ions, we can actually exert a significant degree of control over the interactions and start creating new forms of quantum matter. My group is particularly interested in two types of interactions: electron-electron repulsion, and spin-orbit coupling.

Electron-electron repulsions are relatively weak in the metals we typically encounter in daily life. But under the right circumstances, the repulsions can get really, really big, and the material becomes a high-temperature superconductor. "High temperature" in this context means keeping the material at –135°C instead of –245°C, or in other words, keeping them really cold as opposed to really, really cold. Can a room-temperature superconductor be made? Nobody knows.

The other interaction that interests me is called spin-orbit coupling. Basically, an electron can be either "spin up" or "spin down," and most materials have an equal population of each all swimming around in random directions through the crystal. An atomic nucleus has a positive charge, so it emits an electric field. If the atom is really big and heavy, like lead or bismuth, the field is actually strong enough to torque the spins of passing electrons so that they all leave pointing in the same direction. The importance of spin-orbit coupling was given a huge boost about 10 years ago, when people began to think about so-called "topological order" in crystals. The hallmark of topological objects is that the bulk of that object doesn't carry electricity, but the boundaries carry it almost perfectly. This property cannot be induced in a non-topological system.


Q: What are these quantum phases of matter good for?

A: If you have something that carries electricity almost perfectly, the most straightforward application is microelectronic circuitry. Integrated circuits are made of semiconductors; the electricity that a semiconductor does not conduct gets dissipated as heat, which is why computer rooms are so heavily air-conditioned. A near-perfect conductor would generate very little heat. It could be a very "green" technology, so if you're running huge server farms, like or Google, the energy savings would be tremendous.

Moreover, the current would be spin-polarized—all the electrons' spins would point in the same direction—making topological materials ideal for wiring up spintronic circuits. Spintronics is an emerging computer technology that reads and writes information by using electric fields to manipulate spins, or magnetic fields to manipulate charge.

And if you start to assemble structures from both topological and conventional materials, you may get objects that might be used to build quantum computers.

I'd like to push further. Nobody knows what happens when you create both spin-orbit interactions and electron-electron interactions in the same crystal. A lot of condensed-matter physicists are going in that direction—it's an experimentally unknown territory.

We're also looking for what are called topological superconductors. Topological superconductors are predicted to have the potential to perform quantum computations in a fault-tolerant way, meaning that they would resist perturbations from the outside world that would otherwise crash the computer. There's a huge quantum-computing effort going on at Caltech, and engineering fault tolerance into the system is a key element.


Q: How did you get into this line of work?

A: Well, I wanted to do fundamental physics, but I also hoped to see societal benefits from my research within my lifetime. So I'm idealistic, but there's some pragmatism there, too. When I went to Princeton as a graduate student, I wanted to do experimental tests of string theory. But after a couple of years I grew increasingly attracted to condensed-matter physics, so I changed fields and wound up doing my PhD thesis on topological materials.


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.

Douglas Smith
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TA Training: fall make-up session

Remembering Gerry Neugebauer


Gerry Neugebauer, Caltech's Robert Andrews Millikan Professor of Physics, Emeritus, passed away on September 26, 2014, of complications from spinocerebellar ataxia, a neurodegenerative disease. He was 82. 

Neugebauer was one of the founders of the field of infrared astronomy, the study of astronomical objects using the heat energy they emit.

"Gerry's foundational contributions to infrared astronomy laid the groundwork for the more than $10 billion in investments in this discipline that many countries have made in their infrared space projects, as well as substantial components of ground-based telescopes," says Tom Soifer (BS '68), professor of physics, Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy (PMA) at Caltech, and Neugebauer's protégé and longtime collaborator. "None of this would have happened without the excitement of the discoveries made by Gerry and his students and colleagues."

"During his career, Gerry had a profound impact on JPL and Caltech," says Charles Elachi (MS '69, PhD '71), JPL's director and a professor of electrical engineering and planetary science at Caltech. "He truly was the father of infrared space astronomy."

Neugebauer was born on September 3, 1932, in Göttingen, Germany, to Grete Bruck and Otto Neugebauer, a noted mathematical historian. The family soon relocated to Copenhagen and then to Providence, Rhode Island, in 1939, after Otto took a faculty position at Brown University. The younger Neugebauer earned an AB in physics from Cornell University in 1954 and his PhD in physics from Caltech in 1960, after which he served two years in the United States Army, stationed at JPL. There, he was assigned to work on the infrared instrument on the Mariner 2 space probe, which, upon its arrival at Venus in 1962, became the first successful NASA mission to another planet. 

In 1962, Neugebauer returned to Caltech as an assistant professor of physics and began working with astrophysicist Bob Leighton on the world's first infrared sky survey, the Two-Micron Sky Survey (TMSS). The survey revealed an unexpectedly large number of relatively cool objects, including new stars still surrounded by their dusty pre-stellar shells and supergiant stars in the last stages of their evolution. "This work was a huge milestone in astronomy," Soifer says, "in that it demonstrated that the infrared portion of the electromagnetic spectrum held tremendous excitement and potential for discovery in astronomy."

Neugebauer later led the science team for the first orbiting infrared observatory, the Infrared Astronomical Satellite (IRAS), which conducted the first far-infrared sky survey and eventually detected more than half a million sources of infrared radiation, including numerous galaxies and the debris rings around stars that gave astronomers early hints of the existence of extrasolar planets. He and his colleagues obtained the first infrared view of the galactic center, and he was the codiscoverer, with astrophysicist Eric Becklin (PhD '68) of the Becklin-Neugebauer Object, a massive but compact and intensely bright newly forming star in the Orion Nebula, previously undetected at other wavelengths of light.

"Gerry had original, expansive ideas about how to illuminate the relatively unknown infrared universe," adds France Córdova (PhD '79), the director of the National Science Foundation. "He became one of the first to work with X-ray astronomers to identity mysterious astrophysical sources and encouraged students in both infrared and X-ray fields to work and learn together."

As the chair of the Division of Physics, Mathematics and Astronomy, a position he held from 1988 to 1993, Neugebauer played a key role in the design and construction of the W. M. Keck Observatory in Hawaii, and he participated in the first science run of the first instrument on the Keck 1 telescope, the Near Infrared Camera. From 1980 to 1994, he also served as the director of the Palomar Observatory and spearheaded significant upgrades to the observatory's telescopes.

In addition to his scientific and administrative achievements, Neugebauer was a dedicated educator and mentor. "Gerry was devoted to Caltech, and he was an outstanding teacher," Soifer says. "He participated as one of the junior faculty with the group surrounding Richard Feynman as Feynman did the lectures on physics that are the benchmark of learning physics for all practicing physicists." 

"He had the marvelous capability to sense when you were in trouble on something, and promptly showed up to help," recalls Robbie Vogt, R. Stanton Avery Distinguished Service Professor and Professor of Physics, Emeritus, and a former Caltech provost and PMA division chair, who had an adjoining office with Neugebauer when both joined the Caltech faculty as young assistant professors, and who worked with him on the Feynman lectures.

"Whether he was at the telescope or in the instrument lab, he was hands-on and treated his students like peers," Córdova says. "He was an active listener with helpful advice about the range of a student's concerns. He was always himself and always looked happy, even when he definitely was not, because he loved what he was doing and cared about the people with whom he worked."

"He was a mentor and colleague with great integrity, who got the best out of all who worked with him," adds Becklin, professor of physics and astronomy, emeritus, at the University of California, Los Angeles.

"Gerry was the chair of PMA at Caltech during five years while I was president. The personal sensitivity that his students describe, he extended to all members of his division during his chairmanship," says Thomas E. Everhart, president emeritus and professor of electrical engineering and applied physics, emeritus. "He was an excellent representative in the Institute Academic Committee, explaining the science in his division to the other chairs, the provost, and me, and he was instrumental in establishing the leadership of the LIGO [Laser Interferometer Gravitational-wave Observatory] project on campus after the award from the National Science Foundation, as well as overseeing many other projects in PMA. He was not only a great scientist but also answered the call of his division to provide it leadership. He has been greatly missed since disease shortened his spectacular career at Caltech."

"Simply put, he was one of the greatest scientists and human beings I know, and I will forever be grateful for having had the opportunity to work with him," says Andrea Ghez (MS '89, PhD '93) of the University of California, Los Angeles, an advisee of Neugebauer's and the discoverer of a supermassive black hole at the center of our galaxy.

"He was the best mentor one could possibly hope for," she says. "I learned from him what it means to be a scientist: how to ask good scientific questions, how to design an experiment that can actually answer the question you've asked, the importance of a completely rigorous analysis and communicating clearly what you have done. He held himself and everyone around him to incredibly high standards and was absolutely devoted to the pure pursuit of science. He was not only a great scientist who was so willing to do the things that were uncharted, but he was also a tremendous human being who cared deeply for those around him. His influence was, and will continue to be, immense, both in the field of astronomy and on those of us fortunate enough to work with him.

"Gerry was a magnificent mentor and teacher," adds Soifer. "He inspired, pushed, taught how to do science with integrity and have fun. He never expected more from his students than he did of himself. For me, he was an inspiration, from when I worked on the two-micron survey as an undergraduate, to collaborating with him in many scientific endeavors, to watching him handle the intractable problems of guiding the IRAS science team through many trials and tribulations both technical and political, to watching him guide Palomar and the division, to watching him handle with grace the debilitating condition that he suffered from for the last two decades of his life. He was a wonderful counselor and valued friend."

Neugebauer was a member of the National Academy of Sciences, the American Philosophical Society, and the American Academy of Arts and Sciences and was a fellow of the Royal Astronomical Society. His numerous prizes included the Rumford Prize of the American Academy of Arts and Sciences (1986), the Herschel Medal of the Royal Astronomical Society (1998), the Space Science Award of the American Institute of Aeronautics and Astronautics (1985), two NASA Exceptional Scientific Achievement awards (1972 and 1984), and lifetime achievement awards from the American Astronomical Society (the Henry Norris Russell Lectureship, 1996) and the Astronomical Society of the Pacific (the Catherine Wolfe Bruce Medal, 2010). He was named California Scientist of the Year in 1986.

He is survived by his wife, Marcia Neugebauer, a geophysicist at JPL; daughters Carol Kaplan and Lee Neugebauer; and two granddaughters.

Kathy Svitil
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Alumnus Eric Betzig Wins 2014 Nobel Prize in Chemistry

Eric Betzig (BS '83), a group leader at the Howard Hughes Medical Institute's Janelia Farm Research Campus in Ashburn, Virginia, has been awarded the 2014 Nobel Prize in Chemistry along with Stefan W. Hell of the Max Planck Institute for Biophysical Chemistry and William E. Moerner of Stanford University. The three were honored "for the development of super-resolved fluorescence microscopy," a method that allows for the creation of "super-images" with a resolution on the order of nanometers, or billionths of a meter. In essence, the work turns microscopy into "nanoscopy."

The technique developed by the trio overcomes the so-called Abbe diffraction limit, which describes a physical restriction on the sizes of the structures that can be resolved using optical microscopy, showing that, essentially, nothing smaller than one-half the wavelength of light, or about 0.2 microns, can be discerned by these scopes. The result of the Abbe limit is that only the larger structures within cells—organelles like mitochondria, for example—can be resolved and studied with regular microscopes but not individual proteins or even viruses. The restriction is akin to being able to observe the buildings that make up a city but not the city's inhabitants and their activities.

Betzig, building on earlier work by Hell and Moerner, found that it was possible to work around the Abbe limit to create very-high-resolution images of a sample, such as a developing embryo, by using fluorescent proteins that glow when illuminated with a weak pulse of light. Each time the sample is illuminated, a different, sparsely distributed subpopulation of fluorescent proteins will light up and, because the glowing molecules are spaced farther apart than the Abbe diffraction limit, a standard microscope would be able to capture them. Still, each of the images produced in this way has relatively low resolution—that is, they are blurry. Betzig, however realized that by superimposing many such images, he would be able to obtain a sharp super-image, in which nanoscale structures are clearly visible. The new technique was first described in a 2006 paper published in the journal Science.

After Caltech, Betzig, a physics major from Ruddock House, earned an MS (1985) and a PhD (1988) from Cornell University. He worked at AT&T Bell Laboratories until 1994, when he stepped away from academia and science to work for his father's machine tool company. Betzig returned to research in 2002 and joined Janelia in 2005.

To date, 33 Caltech alumni and faculty have won a total of 34 Nobel Prizes. Last year, alumnus Martin Karplus (PhD '54) also received the Chemistry Prize. 

Kathy Svitil
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