Of Quasar Winds and Other Galactic Challenges

By Joe Sugarman

T he evening was not going well for astrophysicist Nadia Zakamska.

On the cold December night in 2010, she was scheduled for observation time on the Gemini telescope on Mauna Kea in Hawaii. Her proposal was to use the telescope’s new integral field unit spectrometer to collect data on quasar winds, a fresh approach that allows for simultaneous collection of about a thousand spectra of the different parts of an astronomical object; standard fiber spectroscopy, by contrast, gives astrophysicists only one spectrum for an entire astronomical object. But there was an ice storm on the mountain—bad news for good observations—as well as technical issues with the equipment. To make matters worse, once she began collecting data, she was forced to stop. “Another team interrupted our program with something called a target of opportunity observation,” recalls Zakamska, who was a research associate at Stanford University at the time. “Somewhere a supernova went off, and because this was a time-sensitive event, the other team had priority. I was heartbroken. Here’s my precious observing time and all this stuff was happening!”

“The active black hole becomes a bomb which sends blast waves through the galaxy.”
—Assistant Professor Nadia Zakamska

But when she finally did get her time on the telescope, the results were spectacular. “Immediately, I could tell that something interesting was going on,” says Zakamska, who arrived at Johns Hopkins in 2011 as an assistant professor. “We finally saw those wind signatures that we had been looking for.”

Because of the complexity of the integral field approach, it would be nearly three years before Zakamska and her team crunched all the data and published a series of papers on their observations. Her efforts were rewarded by the American Astronomical Society with the 2014 Newton Lacy Pierce Prize for outstanding astronomical observation achievements by a young astrophysicist over the past five years. The award committee cited her work in observing quasar winds as well as her in-depth observations of Type 2 quasars, the subject of her graduate thesis.

“It never occurred to me that the [Pierce Prize] was a likely thing to happen,” says Zakamska, who was pregnant with her third child when the first quasar wind papers were published, making her unable to present her research at international conferences. “I knew we were doing really exciting stuff, but it was poorly publicized. ... I received this email from David Helfand, the previous president of the AAS and I just didn’t believe it. For a moment, I thought somebody was impersonating him.”

Zakamska and her team now have more than a dozen programs on Gemini and other telescopes and continue to publish papers on quasar winds, a phenomenon occurring in galaxies with active central black holes. As matter gets sucked into a black hole, it produces vast amounts of radiation, which exerts pressure on material around it, resulting in an outflowing wind of surrounding material. “The active black hole becomes a bomb which sends blast waves through the galaxy,” says Zakamska, who studies the effect quasar winds have on the galaxy as a whole, as the winds push matter farther and farther away from the nucleus.

There are still many questions to answer about the nature of quasar winds, from trying to figure out at what point during the evolution of the galaxy the wind starts to how long it lasts to how it affects various processes like star formation—“all very important questions for understanding galaxy evolution,” she says. “In particular, we think this process limits the maximal possible mass of galaxies in the universe.”

Before she started investigating quasar winds, the bulk of Zakamska’s research focused on Type 2 quasars, a certain type of quasar obscured by gas and dust close to the nucleus. As a graduate student at Princeton, using data from the first Sloan Digital Sky Survey, she discovered a large population of Type 2 quasars, objects theorized to exist but of which only a handful were known. “[At the time], they were rare enough that people weren’t taking them seriously,” says Zakamska, who used data from Sloan to look for specific spectral signatures, proving the existence of the new type of quasar. “It’s one thing to discover that something happens rarely in the universe, it’s another thing to discover that it commonly happens. We found that these objects are quite common.”

In addition to her research on quasars, Zakamska and a team of Johns Hopkins undergraduates have begun using data from the third generation of the Sloan Survey to investigate the structure of our own galaxy—measuring its spiral structure and the amount of dark matter mass in its halo. If this line of research seems completely unrelated to her past work on quasars, it’s because it is.

“I like to hedge my bets,” she admits, with a laugh. “I like to do things that are completely new. I wonder if anybody has done X. If nobody has, then that’s what I want to do. The data on galactic structure is so new and so different from what anyone has done before; it seems like a very ripe space for discovery.”

Artist’s rendering of the environment around a supermassive black hole. The broad outflow seen in the Gemini data is shown as the fan-shaped wedge at the top of the accretion disk around the black hole.
—Artist L. Coo /Gemini Observatory

Harnessing the Potential of Spin

Chia-Ling Chien makes new discoveries in magnetic physics

By Gabriel Popkin

The information technology revolution of the last quarter century has been built almost entirely on one property of the fundamental electron: its electric charge. But thanks to quantum mechanics, the electron also has a tiny magnetic moment, or spin, that can point “up” or “down,” and that could serve as an information carrier. “Spin so far is ignored in manipulation of data,” laments Chia-Ling Chien, the Jacob L. Hain Professor.

Chien’s research is helping to tap spin’s long-neglected promise. His work could lead to advances that dramatically reduce the heat generated by modern electronics and that speed up computer memory. For Chien, however, harnessing spin’s potential is just the latest effort in a 30-year career that has touched on almost every branch of magnetism, from superconductivity to giant magnetoresistance to exotic new magnetic materials.

Quantum spin invokes magnetism at its most basic. It gives fundamental particles tiny amounts of rotational or angular momentum, even if the particles themselves are point particles, meaning they cannot “spin” in the conventional sense.

In today’s computer technology, waste heat from electric currents in microcircuits is now the main barrier to faster computer processors, Chien says, so finding a more efficient way to transmit digital information is a major industry goal. For example, in a pure spin current, two electrons with opposite spin travel in opposite directions down a wire. The net result is that two units—or “quanta”—of angular momentum flow in the same direction, in the same way that if a positive charge moves in one direction while a negative charge moves in the other, there is a net transfer of two units of positive charge, but in the case of the spin current no net electrical current flows, thereby reducing heat generation.

But spin current is fickle and not easily controlled. Send an electron down a 10-mile wire and its electric charge will be the same on the other end. Its spin, by contrast, will have flipped within less than a hundred microns in the best known materials, due to random interactions with the environment. Chien is working to design new materials that can carry spin currents longer distances without loss of the spin orientation. He is also improving methods for transferring spin information to and from conventional electric circuits.

Professor Chia-Ling Chien

Chien is also excited about an exotic new magnetic structure, the skyrmion. Predicted in the 1960s and finally discovered a few years ago, the skyrmion breaks all the rules of traditional ferromagnets: In its low-energy state, for example, its magnetic spins point in a spiral instead of aligning linearly. Chien’s research group was the first to create a thin-film skyrmion, a necessary step toward any future device application. He is now trying to determine if skyrmions can sustain long-lasting spin currents, as some theorists have predicted.

In addition to helping manipulate data, spin current could open up new ways to store information. Chien studies magnetic tunnel junctions, which take advantage of a property called quantum tunneling, whereby electrons can bridge a tiny energy gap between two materials. Tunnel junctions have the potential to be used as “magnetoresistive random access memory,” or MRAM, which, unlike the RAM in your computer, would be stable even when the computer is off. (Commercial hard drives already use magnetic tunnel junctions, but they operate too slowly to be used as RAM).

Development of MRAM has been hampered, however, because the electric currents needed to operate today’s junctions are so large that they can damage or destroy the stored information. Chien discovered that a much smaller spin current, in concert with a small voltage, can do the job while preserving the stored data. His insight could aid companies that are racing to introduce the long-sought “universal memory.”

Chien emphasizes that as a research physicist, his goal is not to create commercial products. His job is to explore. If one of his results hints at a practical application, he passes the idea to engineers who look for a way to mass-produce it. For many years Chien collaborated with engineers through a National Science Foundation-funded Materials Research Science and Engineering Center at Johns Hopkins. “We can explore things; the worst thing is we fail,” Chien says. Industry scientists “don’t take such risks.”

Chien’s ideas have ranged widely within magnetic physics. In 1992, inspired by the 1988 discovery of giant magnetoresistance in layered structures (which set off a revolution in hard drive technology and was recognized with the 2007 Nobel Prize in Physics), Chien showed that the effect also occurs in granular systems, debunking theories that the multi-layered structure was responsible for the effect.

Chien has also studied superconductivity, the property that allows some materials, when cooled to low temperatures, to conduct electricity without resistance. When a new class of iron-based superconductors was fortuitously discovered in 2008 in Japan, Chien was among the first U.S.-based scientists to obtain samples, and showed that the materials displayed an important symmetry property.

Chien has published more than 400 journal articles, and he is a Fellow of the American Physical Society. He is also a Fellow of the American Association for the Advancement of Science and a 2004 recipient of the David Adler Award of the American Physical Society. But Chien says he is proudest not of the papers that have come out of his lab, but of his students. “Two thirds of them are now university faculty. The rest are in government labs or industrial labs, and they’re all doing very well. That gives me a great deal of pride.”

“Spin so far is ignored in manipulation of data.”

That his students have done so well is no accident, though. Chien drills them in how to present their research at conferences and seminars. “The same material, if you give it to different people, the delivery will be totally different. One will knock your socks off; another one could bore you to death,” he says. When coaching a student on a presentation, he says, “I may want to hear it three, five, seven, or even more times, until they get it right.”

One of Chien’s colleagues at Hopkins, theorist Oleg Tchernyshyov, recalls an anecdote: “Every time Chia-Ling comes in in the morning, he goes into the lab and asks what’s new. They have to be prepared to tell him something interesting that has happened in their research project. His students are trying hard to surprise him with something interesting.”

With characteristic modesty, Chien also attributes his success to picking the right field at the right time. “I’ll tell you a true story,” he says. “In 1984, when I was a much younger man, a famous physicist visited the department. He asked, ‘What do you do?’ I said ‘I work on magnetism,’ and he said, ‘That field is dead.’ I said ‘I also work on superconductivity;’ he said, ‘That field is also dead.’ What he didn’t know is that in 1986, the first [high-temperature] superconductor would be discovered. In 1988 [giant magnetoresistance] was discovered…Since 1988 there has been a flurry of activity [in magnetism that has lasted] to this day.”

“In that sense I was very lucky,” he says. “This thing has been going on for 25 years, my whole career.”

Filming Physics

How the documentary “Particle Fever” brought physics to the masses

Interview by Joe Sugarman

Johns Hopkins theoretical physicist David Kaplan has had an eventful year. “Particle Fever,” the documentary he produced and starred in continues to receive praise for making complicated scientific discoveries accessible and for illustrating how thrilling the Higgs boson discovery was. The film, which has qualified for an Academy Award, could receive an official nomination come January. But when we spoke with Kaplan over the phone in late August, he was unpacking, preparing for a year-long sabbatical at Stanford University, and filmmaking was the furthest thing from his mind. “I just want to sit around and talk physics until we hopefully discover something,” he said. “Not only did the movie have a dramatic effect on me, but it’s such a dramatic time in my field. A lot of people are wondering what to work on next. My goal is to choose the direction of my research for the next five years.” In the meantime, we had a few questions for Kaplan about his film, the Large Hadron Collider, and the future of his field.

Professor and theoretical physicist David Kaplan’

Q: So how did you go about making particle physics compelling in the movie?

A: The core was that we really wanted to make this a story about a group of people [primarily experimental and theoretical physicists] who were doing something at a dramatic time. … The number one goal in terms of structure was to introduce the characters first. You first have to like the people, and then you’re interested in what they’re doing because you have an attachment to them.

Q: How did you decide how much physics to include in the film?

A: We argued a lot in the beginning about how much to set up and what not to set up. Our attitude about the science in the film was that the only physics that goes in should help propel the story forward and not just for the sake of teaching people anything.

Q: Have you heard any criticisms about how you portrayed the science?

A: There’s been some narrow criticism that we didn’t explain enough. Some people watch the film and think they’re watching a Nova special, and they’d like to learn all these things in detail. But that was never the intention. We wanted people to feel like they didn’t have to understand everything, but they got a sense of what was going on, which allowed them to follow characters through events.

Q: Essentially you were making a movie in real time with no idea about how it was going to end. That must have been a little crazy.

A: [Director] Mark Levinson and I had two totally different attitudes that fit together well. His attitude was that at every stage, assuming we’d run out of money or couldn’t continue shooting, could he end the film? Could he use the material he already had and make a movie? He was constantly second guessing what the end would be. For me, I demanded that the movie end once the data from the LHC had an emotional impact on the theorists. The experimentalists would be affected just by the machine working, but I wanted all of the characters to go through something. I started making the movie from the perspective of the theorists—that’s me—so I wanted to make the film on what was learned, not just that this big machine works.

Q: You sound as much a filmmaker as theorist now.

A: I’m trying to recover from that!

Q: Do you think a physicist was the only one who could have made this movie?

A: Yes, for sure. If you come from the outside, you feel like you have to explain the physics, that that’s the important part. Mark has a PhD in physics and I’m in the thick of it, so we knew what the human story was. It’s really hard to see through this complicated vernacular and see the human condition inside of it. The physicist can see what makes it such an interesting time for the field—and focus on the people themselves.

Q: There’s a scene in the film where you confide to the camera that the theory of supersymmetry—your life’s work—might not be true. You comment that that’s “pretty cool.” Do you still feel that way?

A: Oh, yeah. I sort of want nature to scare me. I’d like to figure things out, but supersymmetry is not something I’m attached to. It would be convenient if it were discovered, because I’m an expert on it, and I can give lots of big talks and explain it to people, but I like to learn new things.

Q: What’s the best case scenario when the LHC goes back online?

A: If the LHC sees any new particle or even sees something that is a deviation from what the Standard Model predicts and does so significantly, it’s another transformation. But if nothing new is seen, we really don’t know where the next big discovery or theory will show up. What we do know is that there are deep issues with the Standard Model. It can’t be the complete theory and the most compelling experimental reason for that is dark matter. That already is an indicator that the universe is made of things beyond the Standard Model. The question is, are we going to be able to get information about it?

Q: If nothing new is discovered, is that bad news for particle physics?

A: There is stress in the community that if the LHC doesn’t see anything else and if we don’t build a bigger collider, people are afraid that the field is dead. The motivation to fund it will disappear and people just won’t go into it and progress will be incredibly slow. I’m not quite of that mind. It’s hard for me to believe that in a modern society, there at least won’t be some support for this type of research.

Q: What direction do you see your research taking during the next five years?

A: I have some crazy ideas about what dark matter could be. I don’t want to tell you much because it’s not well-formed. Instead of individual particles, it could be chunky objects made out of a new particle beyond the Standard Model. There are also a lot of people trying to understand black holes again. It’s something I never dove into deeply, so maybe that little slice of the field could use people who think differently and try to figure something out.

Q: Do you foresee more films in your future?

A: Ha! I’m a much happier person when I’m doing physics than making movies. My goal for the next year is to do as much physics as humanly possible.

Big Black Holes Can Block New Stars

By Dennis O'Shea

M assive black holes spewing out radio-frequency-emitting particles at near-light speed can block formation of new stars in aging galaxies, a study by Assistant Professor Tobias Marriage has found.

The research provides crucial new evidence that it is these jets of “radio-frequency feedback” streaming from mature galaxies’ central black holes that prevent hot free gas from cooling and collapsing into baby stars.

“When you look into the past history of the universe, you see these galaxies building stars,” said Marriage, co-lead author of the study. “At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe.”

The findings have been published in the journal Monthly Notices of the Royal Astronomical Society. They were made possible by adaptation of a well-known research technique for use in solving a new problem.

Johns Hopkins postdoctoral fellow Megan Gralla found that the Sunyaev–Zel’dovich effect signature—typically used to study large galaxy clusters—can also be used to learn a great deal about smaller formations. The SZ effect occurs when high-energy electrons in hot gas interact with faint light in the cosmic microwave background, light left over from earliest times when the universe was a thousand times hotter and a billion times denser than today.

“The SZ is usually used to study clusters of hundreds of galaxies but the galaxies we’re looking for are much smaller and have just a companion or two,” Gralla said.

Tobias Marriage & Megan Gralla

“What we’re doing is asking a different question than what has been previously asked,” Gralla said. “We’re using a technique that’s been around for some time and that researchers have been very successful with, and we’re using it to answer a totally different question in a totally different subfield of astronomy.”

“I was stunned when I saw this paper, because I’ve never thought that detecting the SZ effect from active galactic nuclei was possible,” said Eiichiro Komatsu, director of the Max Planck Institute for Astrophysics in Germany and an expert in the field who was not involved in the research. “I was wrong. … It makes those of us who work on the SZ effect from galaxy clusters feel old; research on the SZ effect has entered a new era.”

In space, hot gas drawn into a galaxy can cool and condense, forming stars. Some gas also funnels down into the galaxy’s black hole, which grows together with the stellar population. This cycle can repeat continuously; more gas is pulled in to cool and condense, more stars begin to shine, and the central black hole grows more massive.

But in nearly all mature galaxies —the big galaxies called “elliptical” because of their shape—that gas doesn’t cool any more. “If gas is kept hot, it can’t collapse,” Marriage said. When that happens: No new stars.

Marriage, Gralla, and their collaborators found that the elliptical galaxies with radio-frequency feedback—relativistic radio-frequency-emitting particles shooting from the massive central black holes at their center at close to the speed of light—all contain hot gas and a dearth of infant stars. That provides crucial evidence for their hypothesis that this radio-frequency feedback is the “off switch” for star-making in mature galaxies.

Marriage said, however, that it is still not known just why black holes in mature elliptical galaxies begin to emit radio-frequency feedback. “The exact mechanism behind this is not fully understood and there are still debates,” he said.