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Kip Thorne Discusses First Discovery of Thorne-Żytkow Object

In 1975, Kip Thorne (BS '62, and the Richard P. Feynman Professor of Theoretical Physics, Emeritus) and then-Caltech postdoctoral fellow Anna Żytkow sought the answer to an intriguing question: Would it be possible to have a star that had a neutron star as its core—that is, a hot, dense star composed entirely of neutrons within another more traditional star? Thorne and Żytkow predicted that if a neutron star were at the core of another star, the host star would be a red supergiant—an extremely large, luminous star—and that such red supergiants would have peculiar abundances of elements. Researchers who followed this line of inquiry referred to this hypothetical type of star as a Thorne-Żytkow object (TŻO).

Nearly 40 years later, astronomers believe they may have found such an object: a star labeled HV 2112 and located in the Small Magellanic Cloud, a dwarf galaxy that is a near neighbor of the Milky Way and visible to the naked eye. HV 2112 was identified as a TŻO candidate with the 6.5-meter Magellan Clay telescope on Las Campanas in Chile by Emily Levesque (University of Colorado), Philip Massey (Lowell Observatory; BS '75, MS '75, Caltech), Żytkow (now at the University of Cambridge), and Nidia Morrell (also at the University of Cambridge).

We recently sat down with Thorne to ask how it feels to have astronomers discover something whose existence he postulated decades before.

When you came up with the idea of TŻOs, were you trying to explain anything that had been observed, or was it a simple "what if?" speculation?

It was totally theoretical. We weren't the first people to ask the question either. In the mid-1930s, theoretical physicist George Gamow speculated about these kinds of objects and wondered if even our sun might have a neutron star in its core. That was soon after Caltech's Fritz Zwicky conceived the idea of a neutron star. But Gamow never did anything quantitative with his speculations.

The idea of seriously pursuing what these things might look like was due to Bohdan Paczynski, a superb astrophysicist on the faculty of the University of Warsaw. In the early 1970s, he would shuttle back and forth between Caltech, where he would spend about three months a year, and Warsaw, where he stayed for nine months. He had a real advantage over everybody else during this era when people were trying to understand stellar structure and stellar evolution in depth. Nine months of the year he didn't have a computer available, so he had to think. Then during the three months he was at Caltech, he could compute.

Paczynski was the leading person in the world in understanding the late stages of the evolution of stars. He suggested to his postdoctoral student Anna Żytkow that she look into this idea of stars with neutron cores, and then Anna easily talked me into joining her on the project, and came to Caltech for a second postdoc. I had the expertise in relativity, and she had a lot better understanding of the astrophysics of stars than I did. So it became a very enjoyable collaboration. For me it was a learning process. As one often does as a professor, I learned from working with a superb postdoc who had key knowledge and experience that I did not have.

What were the properties of TŻOs as you and Żytkow theorized them?

We didn't know in advance what they would look like, though we thought—correctly it turns out—that they would be red supergiants. Our calculations showed that if the star was heavier than about 11 suns, it would have a shell of burning material around the neutron core, a shell that would generate new elements as it burned. Convection, the circulation of hot gas inside the star, would reach right into the burning shell and carry the products of burning all the way to the surface of the star long before the burning was complete. This convection, reaching into a burning shell, was unlike anything seen in any other kind of star.

Is this how you get different elements in TŻOs than those ordinarily seen on the surface of a star?

That's right. We could see that the elements produced would be peculiar, but our calculations were not good enough to make this quantitative. In the 1990s, a graduate student of mine named Garrett Biehle (PhD '93) worked out, with considerable reliability, what the products of nuclear burning would be. He predicted unusually large amounts of rubidium and molybdenum; and a bit later Philipp Podsiadlowski, Robert Cannon, and Martin Rees at the University of Cambridge showed there would also be a lot of lithium.

It is excess rubidium, molybdenum, and lithium that Żytkow and her colleagues have found in HV 2112.

Does that mean TŻOs are fairly easy to recognize with a spectrographic analysis, which can determine the elements of a star?

No, it's not easy! TŻOs should have a unique signature, but these objects would be pretty rare.

What are the circumstances in which a TŻO would develop?

As far as we understand it, the most likely way these things form is that a neutron star cannibalizes the core of a companion star. You have a neutron star orbiting around a companion star, and they spiral together, and the neutron star takes up residence in the core of the companion. Bohdan Paczynski and Jerry Ostriker, an astrophysicist at Princeton University, speculated this would happen way back in 1975 while I was doing my original work with Żytkow, and subsequent analyses have confirmed it.

The other way a TŻO might develop is from the supernova explosion that makes the neutron star. In a supernova that creates a neutron star, matter is ejected in an asymmetric way. Occasionally these kicks resulting from the ejection of matter will drive the neutron star into the interior of the companion star, according to analyses by Peter Leonard and Jack Hills at Los Alamos, and Rachel Dewey at JPL.

Is there anything other than peculiar element abundances that would indicate a TŻO? Does it look different from other red supergiant stars?

TŻOs are the most highly luminous of red supergiant stars but not so much so that you could pick them out from the crowd: all red supergiants are very bright. I think the only way to identify them is through these element abundances.

Are you convinced that this star discovered by Żytkow and her colleagues is a TŻO?

The evidence that HV 2112 is a TŻO is strong but not ironclad. Certainly it's by far the best candidate for a TŻO that anyone has seen, but additional confirmation is needed.

How does it feel to hear that something you imagined on paper so long ago has been seen out in the universe?

It's certainly satisfying. It's an area of astrophysics that I dipped into briefly and then left. That's one of the lovely things about being a theorist: you can dip into a huge number of different areas. One of the things I've most enjoyed about my career is moving from one area to another and learning new astrophysics. Anna Żytkow deserves the lion's share of the credit for this finding. She pushed very hard on observers to get some good telescope time. It's her tenacity more than anything else that made this happen.

What are you working on now that you are retired?

I'm an executive producer of the film Interstellar, directed by Christopher Nolan and based in part on the science I've done during my Caltech career. Greater secrecy surrounds Interstellar than most any movie that's been done in Hollywood. I'm not allowed to talk about it, but let's just say that I've been spending a lot of my time on it in the last year. And I've recently finished writing a book about the science in Interstellar.

The other major project I'm wrapping up is a textbook that I've written with Roger Blandford [formerly a professor at Caltech; now on the faculty at Stanford]: Modern Classical Physics. It's based on a course that Roger or I taught every other year at Caltech from 1980 until my retirement in 2009. It covers fluid mechanics, elasticity, optics, statistical physics, plasma physics, and curved space-time—that is, everything in classical physics that any PhD physicist should be familiar with, but usually isn't. This week we delivered the manuscript to the copy editor. After 34 years of developing this monumental treatise/textbook, it's quite a relief.

I'm also working with some of my former students and postdocs on trying to understand the nonlinear dynamics of curved space-time. For this we gain insights from numerical relativity: simulations of the collisions of spinning black holes. But I've had to shelve this work for the past half year due to the pressures of the movie and books. I hope to return to it soon.

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Tuesday, July 29, 2014
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40-Year Service Awardees

Caltech Staff Service Awards 2014

The 59th Annual Staff Service Awards will be presented in Beckman Auditorium on Monday, June 2, at 10 a.m. During the ceremony, more than 250 staff members whose service ranges from 10 to 50 years will be honored. A full list of awardees can be found here.

This week we are featuring Caltech staff members who will be recognized for 40 and 45 years of service to the Institute.

 

The honorees include three 40-year staff members: Eugene Akutagawa, a senior scientist in biology and a member of the professional staff; Susi Martin, assistant to the Board of Trustees; and Steve Vass, a senior instrument specialist at the Laser Interferometer Gravitational-wave Observatory (LIGO).

 

Eugene Akutagawa graduated from UCLA with a bachelor's degree in microbiology; a help-wanted ad in the Los Angeles Times for a lab assistant brought him to Caltech, where "I was standing in the hallway, waiting to be interviewed, and there's [Nobel Laureate] Max Delbrück coming out of the lab. To me, a microbiologist, he was like a god, and there he was, right in my face—so I knew this place was going to be great. And I liked its smallness, especially contrasted with UCLA, where undergraduate biology classes were 700 or 800 people spilling into the aisles."

Nevertheless, his first job proved unrewarding. "I was implanting electrodes in rats and watching them press the lever until they pooped out," Akutagawa recalls. (The lab belonged to Research Associate Marianne Olds, whose husband, Bing Professor of Behavioral Biology James Olds, had discovered the brain's pleasure center more than two decades earlier.) "Then one day, I was sitting in the parking lot eating my lunch, and a mockingbird landed on a bush and started singing his heart out. I thought, 'I know he's not really singing words, but he's communicating. It would be interesting to study that.' And lo and behold, within a few months Mark Konishi [now the Bing Professor of Behavioral Biology, Emeritus] came here from Princeton."

Konishi had already made a name for himself studying songbirds and owls, so Akutagawa changed labs. The job interview was informal, Akutagawa recalls. "Mark said, 'What experience do you have?' And I said, 'Well, when I was growing up in Hawaii, I tried to save nestlings that had fallen out of their nests.' And he looked at me very sternly and said, 'What did you feed them?' I said, 'Rice. And water.' 'Did any of them live?' 'Nope. They all died.' I think he appreciated my honesty. He never told me I got the job, but he went over to the chalkboard and drew a football shape. He said, 'That's canary seed. That goes to canaries and white-crowned sparrows.' And he drew a little circle, and he says, 'That's millet. That goes to the finches.'"

Within a decade Akutagawa had become a full-fledged collaborator, doing the meticulous microscopy needed to trace fine neural circuitry. In 1985, Konishi and Akutagawa published a paper that showed why male zebra finches sing and females don't: specialized neurons in the male's brain flourish and develop many connections, but in females they atrophy and die. Says Akutagawa, "Our relationship eventually evolved into me doing my own independent research. It's been quite a ride, I must say." The ride, however, is nearing its end; Konishi has retired, and Akutagawa will be following suit.

"I love this job," Akutagawa continues. "It's more like a hobby. It's just an amazing place to work, in large part because Mark was just an incredible supervisor. He gave us a lot of freedom, which spurs a lot of good science."

 

Susi Martin works in the Caltech president's office as assistant to the Board of Trustees. The Board has 85 members and meets five times a year, and Martin manages their comings and goings. She says, "I arrange transportation to and from the airport, hotels, whatever assistance they need. It could be anything." During her tenure, she's moved from a Selectric typewriter to a Filemaker Pro database to the Internet; from three-ring binders to PDFs.

Martin began her Caltech career in the procurement division at JPL before joining the office of then-director Bruce Murray. After a special assignment supporting the Seasat mission's Failure Review Board in 1978, she moved on to one of JPL's early biomedical technology projects before transferring to the Lab's office of planning and review. It was there in April, 1981 that Hardy Martel (BS '49, PhD '56), an electrical engineering professor and the secretary to Caltech's Board of Trustees, called to inquire whether she'd consider moving to campus. One of Martin's former colleagues in the director's office, Mary Webster, had joined the staff of Caltech president Marvin Goldberger earlier that year; when Martel became in need of an assistant, Webster had recommended Martin.

From 1988 to 1994, Martin also served first as assistant secretary and then secretary to the board of directors of the California Association for Research in Astronomy (CARA), a partnership set up by Caltech and the University of California to build and operate the W. M. Keck Observatory on the summit of Mauna Kea.

"I love working with the trustees," Martin says. "It is an honor and a delight—they are a truly remarkable group of individuals, and it is a privilege to facilitate their work on behalf of Caltech." Over the past 33 years, no two days have been the same, she says. "The challenges have been interesting, but the rewards have been awesome and tremendously diverse." For example, Martin was at JPL for the landing of the Mars rover Curiosity, staffing one of the rooms set up for the trustees. "Seeing that first image of the rover's shadow cast on the surface was just amazing," she recalls. "To see something nobody else had ever seen—to be a part of that history—was so cool."

 

While Akutagawa and Martin have essentially stayed put, Steve Vass has occupied eight different offices in three of Caltech's academic divisions. Vass was born and raised in Hungary, where he learned electronics at a trade school. "I had some college but not too much." He eventually came to the United States, where he landed a job in Caltech's biology division in the laboratory of then-professor Leroy Hood (BS '60, PhD '68). Vass helped Hood and postdoc Michael Hunkapiller (PhD '74) build the protein sequenator, which automatically determines the sequence of amino acids that make up a protein. Two decades later, this machine and the other ones developed in the Hood lab—the protein synthesizer, the DNA synthesizer, and the DNA sequenator—would spark the biotech revolution of the 1990s.

In the early 1980s, Vass moved to the Division of Chemistry and Chemical Engineering, where he built X-ray diffractometers for physical chemist Richard Dickerson. Dickerson used them to make high-precision measurements of DNA's crystal structure—both its usual right-handed spiral and the less common left-handed form.

In 1987, Vass moved again—to the Division of Physics, Mathematics and Astronomy and the LIGO project. LIGO searches for the gravitational waves that Einstein predicted would be generated by the motions of extremely massive bodies—colliding black holes being an oft-cited example. The detector consists of twin interferometers, each with a perpendicular set of 4-kilometer-long arms, that were built in Louisiana and Washington in the late 1990s. When Vass joined the project, the design's details were being worked out in a prototype interferometer with 40-meter arms that had been built on the Caltech campus. Nearly two decades later, the 40-meter prototype remains the proving ground for next-generation ideas.

Vass describes how LIGO changed his perspective: "In biology, people said, 'Oh, if we only had a good chemist, we would hit it out of the park.' Then in chemistry they said, 'Oh, if we had a really good electronics guy, we would be just the best.' But in physics, they say, 'We know everything. We can do it ourselves.'"

"Basically, I run the lab, but the fun part is you get to do everything. This morning, I've been hunting for 'ground loops.' The east end of the interferometer has a 60-Hertz hum, which is line current, and it's ruining the spectrum. So I'm going around with an ohmmeter looking for something disconnected—or something connected that shouldn't be. My job is to prepare the best possible environment to get good science done."

LIGO measures the distance between suspended mirrors to within a billionth of the diameter of an atom by bouncing a laser beam between them, so Vass begins his mornings making sure the interferometer hasn't lost lock. "If people stayed really late the night before, things will be fine," he says. "But if they left at 10 p.m., everything will have drifted a little. And earthquakes affect the machine. It's much better designed against quakes now, but in earlier days if we had a local magnitude 4, our precious glass might have fallen and gotten chipped, or our mirror coating could have been ruined. Back then it was a baby, and I've seen it grow up with my kids. I have grandkids now, and someday LIGO will produce something, too—some cosmic event will happen close by, and we'll see it."

"I have to say thank you to all the people who've helped me grow," Vass concludes. "I've learned a lot here and had a lot of fun doing it."

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Douglas Smith
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Tuesday, July 22, 2014
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Teaching Quantum Mechanics with Minecraft and Comics

Supernova Caught in the Act by Palomar Transient Factory

Supernovae—stellar explosions—are incredibly energetic, dynamic events. It is easy to imagine that they are uncommon, but the universe is a big place and supernovae are actually fairly routine. The problem with observing supernovae is knowing just when and where one is occurring and being able to point a world-class telescope at it in the hours immediately afterward, when precious data about the supernova's progenitor star is available. Fortunately the intermediate Palomar Transient Factory (iPTF) operated by Caltech scans the sky constantly in search of dramatic astrophysical events. In 2013, it caught a star in the act of exploding.

The iPTF is a robotic observing system mounted on the 48-inch Samuel Oschin Telescope on Palomar Mountain. It has been scanning the sky since February 2013. The iPTF (and its predecessor experiment, the Palomar Transient Factory [PTF], which operated between 2009 and 2012) regularly observes a wide swath of the night sky looking for astronomical objects that are moving and developing quickly, such as comets, asteroids, gamma-ray bursts, and supernovae. Both the earlier PTF and the current iPTF collaborations are led by Shrinivas Kulkarni, the John D. and Catherine T. MacArthur Professor of Astronomy and Planetary Science and director of the Caltech Optical Observatories.

Last year the iPTF discovered an object of special interest: a supernova with a spectral signature suggesting that its progenitor star was a Wolf-Rayet star. Massive stars are typically structured like an onion, with the heaviest elements in the core, while lighter elements are layered over them and then frosted, if you will, by a layer of hydrogen gas on the stellar surface. Wolf-Rayet stars, which are unusually large and hot, are exceptions to this rule, being relatively deficient in hydrogen and characterized by strong stellar winds. Astronomers have long wondered if Wolf-Rayet stars are the progenitors of certain types of supernovae, and according to a recent paper published in Nature this is just what the iPTF found in May 2013.

This supernova, SN2013cu, was picked up on a routine sky scan by the iPTF. The on-duty iPTF team member in Israel promptly sounded an alert, asking colleagues at the W. M. Keck Observatory on Mauna Kea to take a spectral image of the supernova before the sun rose in Hawaii.

When supernovae explode, they briefly ionize the sky immediately around them. The ionized materials rapidly recombine, producing unique spectral features that enable astronomers to get a full picture of the ambient material of a supernova event. This process lasts from minutes to a few days and hence is called a "flash spectrum" of the event. Flash spectrography is a novel observational method developed by Avishay Gal-Yam of the Weizmann Institute of Science in Israel, leader of the team that published the Nature paper.

In the case of SN2013cu, the flash spectrum showed relatively less hydrogen and relatively more nitrogen, suggesting that perhaps the progenitor of the supernova was a nitrogen-rich Wolf-Rayet star. This finding will enable astronomers to better understand the evolution of massive stars and identify potential progenitors of supernovae.

"I could not believe my eyes when I saw those high-ionization features perfectly matching emission lines from a Wolf-Rayet star," says Yi Cao, a graduate student from Caltech who works with Kulkarni. "Our software pipeline efforts were paying off. Now we are working even harder so that we can get flash spectra of many more supernova flavors to probe their progenitor stars."

Above all, the observation of SN2013cu highlights the success of the intermediate Palomar Transient Factory at catching the universe in the act of doing something interesting, something that might merit a second look. Though especially intriguing, SN2013cu is only one of over 2,000 supernovae that PTF/iPTF has detected during its four and a half years of observations. As Kulkarni remarks, "I am proud of how the global iPTF network is working together to invent new techniques enabling entirely new science."

The iPTF is a collaboration between Caltech, Los Alamos National Laboratory, the University of Wisconsin–Milwaukee, the Oskar Klein Centre, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe.

Coauthors on the paper, "A Wolf-Rayet-like progenitor of supernova SN 2013cu from spectral observations of a wind," include Kulkarni, Cao, Mansi Kasliwal, Daniel Perley, and Assaf Horesh of Caltech; Gal-Yam, I. Arcavi, E. O. Ofek, S. Ben-Ami, A. De Cia, D. Tal, P. M. Vreeswijk, and O. Yaron of the Weizmann Institute of Science; S. B. Cenko of NASA's Goddard Space Flight Center; J. C. Wheeler and J. M. Silverman of the University of Texas at Austin; F. Taddia and J. Sollerman of Stockholm University; P. E. Nugent of the Lawrence Berkeley National Laboratory; and A. V. Filippenko of UC Berkeley.

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Tricking the Uncertainty Principle

Caltech researchers have found a way to make measurements that go beyond the limits imposed by quantum physics.

Today, we are capable of measuring the position of an object with unprecedented accuracy, but quantum physics and the Heisenberg uncertainty principle place fundamental limits on our ability to measure. Noise that arises as a result of the quantum nature of the fields used to make those measurements imposes what is called the "standard quantum limit." This same limit influences both the ultrasensitive measurements in nanoscale devices and the kilometer-scale gravitational wave detector at LIGO. Because of this troublesome background noise, we can never know an object's exact location, but a recent study provides a solution for rerouting some of that noise away from the measurement.

The findings were published online in the May 15 issue of Science Express.

"If you want to know where something is, you have to scatter something off of it," explains Professor of Applied Physics Keith Schwab, who led the study. "For example, if you shine light at an object, the photons that scatter off provide information about the object. But the photons don't all hit and scatter at the same time, and the random pattern of scattering creates quantum fluctuations"—that is, noise. "If you shine more light, you have increased sensitivity, but you also have more noise. Here we were looking for a way to beat the uncertainty principle—to increase sensitivity but not noise."

Schwab and his colleagues began by developing a way to actually detect the noise produced during the scattering of microwaves—electromagnetic radiation that has a wavelength longer than that of visible light. To do this, they delivered microwaves of a specific frequency to a superconducting electronic circuit, or resonator, that vibrates at 5 gigahertz—or 5 billion times per second. The electronic circuit was then coupled to a mechanical device formed of two metal plates that vibrate at around 4 megahertz—or 4 million times per second. The researchers observed that the quantum noise of the microwave field, due to the impact of individual photons, made the mechanical device shake randomly with an amplitude of 10-15 meters, about the diameter of a proton.

"Our mechanical device is a tiny square of aluminum—only 40 microns long, or about the diameter of a hair. We think of quantum mechanics as a good description for the behaviors of atoms and electrons and protons and all of that, but normally you don't think of these sorts of quantum effects manifesting themselves on somewhat macroscopic objects," Schwab says. "This is a physical manifestation of the uncertainty principle, seen in single photons impacting a somewhat macroscopic thing."

Once the researchers had a reliable mechanism for detecting the forces generated by the quantum fluctuations of microwaves on a macroscopic object, they could modify their electronic resonator, mechanical device, and mathematical approach to exclude the noise of the position and motion of the vibrating metal plates from their measurement.

The experiment shows that a) the noise is present and can be picked up by a detector, and b) it can be pushed to someplace that won't affect the measurement. "It's a way of tricking the uncertainty principle so that you can dial up the sensitivity of a detector without increasing the noise," Schwab says.

Although this experiment is mostly a fundamental exploration of the quantum nature of microwaves in mechanical devices, Schwab says that this line of research could one day lead to the observation of quantum mechanical effects in much larger mechanical structures. And that, he notes, could allow the demonstration of strange quantum mechanical properties like superposition and entanglement in large objects—for example, allowing a macroscopic object to exist in two places at once.

"Subatomic particles act in quantum ways—they have a wave-like nature—and so can atoms, and so can whole molecules since they're collections of atoms," Schwab says. "So the question then is: Can you make bigger and bigger objects behave in these weird wave-like ways? Why not? Right now we're just trying to figure out where the boundary of quantum physics is, but you never know."

This work was published in an article titled "Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field." Other Caltech coauthors include senior researcher Junho Suh; graduate students Aaron J. Weinstein, Chan U. Lei, and Emma E. Wollman; and Steven K. Steinke, visitor in applied physics and materials science. The work was funded by the Institute for Quantum Information and Matter, the Defense Advanced Research Projects Agency, and the National Science Foundation. The device was fabricated in Caltech's Kavli Nanoscience Institute, of which Schwab is a codirector.

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Ditch Day? It’s Today, Frosh!

Today we celebrate Ditch Day, one of Caltech's oldest traditions. During this annual spring rite—the timing of which is kept secret until the last minute—seniors ditch their classes and vanish from campus. Before they go, however, they leave behind complex, carefully planned out puzzles and challenges—known as "stacks"—designed to occupy the underclass students and prevent them from wreaking havoc on the seniors' unoccupied rooms.

Follow the action on Caltech's Facebook and Twitter pages as the undergraduates tackle the puzzles left around campus for them to solve, and get in on the conversation by sharing your favorite Ditch Day memories. Be sure to use #CaltechDitchDay in your tweets and postings.

View photos from the day:

 

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