March 24, 2016
When scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) made their stunning announcement in February that its detectors had directly observed gravitational waves for the first time ever, few people were more excited than Hertz Fellow Katelin Schutz.
The second-year UC Berkeley graduate student, along with Professor Chung-Pei Ma, already had been working on the problem, albeit at a much different scale. When she first got to Berkeley, Schutz teamed up with Ma to work on synthesizing data from spinning pulsars collected by Pulsar Timing Arrays (PTAs) to identify areas where supermassive black hole binaries might exist within 300 million light years from Earth. The gravitational waves from the most massive nearby black hole binaries, she reasoned, would alter the rhythmic pulses emitted by these extremely dense neutron stars, such that the signals would arrive later or earlier on Earth than they otherwise would. With this method, Schutz and Ma were able to precisely map out and constrain the most likely hosts of such black hole binaries, which, in cosmological time, form quite frequently as galaxies merge. Their paper, “Constraints on Individual Supermassive Black Hole Binaries from Pulsar Timing Array Limits on Continuous Gravitational Waves”, was completed a few months before LIGO’s announcement.
"Angular positions of pulsars from NANOGrav (cyan stars), Parkes PTA (yellow stars), and European PTA (red stars). Also shown are the locations of the most likely hosts of supermassive black hole (SMBH) binaries that could emit detectable continuous gravitational waves (circles). The top plot shows galaxies with measured SMBH masses, while the bottom plot shows the ~100 most massive, nearby galaxies. The latter group make up the MASSIVE survey, and since we know that galaxy mass and SMBH mass are tightly correlated, we can infer that these host galaxies might be gravitational wave hotspots. The shading of the circles represents the potential strength of gravitational waves emitted from each source based on what we know about its properties (i.e. how far away it is, what the total mass of the black holes is, etc.) Strong sources at similar angular positions as pulsars constitute the most promising places to look for gravitational waves using this method."
“As the first ones to do this analysis, we already were able to do meaningful science and actually start to rule out the existence of these binaries in specific host galaxies,” Schutz said. “It has implications for how people should analyze data to look for these gravitational waves in the future and also for how people should improve their pulsar timing arrays. We think these black holes play an instrumental role in the evolution of the galaxy and shaping its properties.”
Schutz’s research differed from LIGO in that she was looking at black holes on a more massive and extreme scale. The discovery, she said, represents the tip of the iceberg. “LIGO’s discovery is really exciting because there are so many unknowns,” she said. “It is encouraging because it means gravitational waves are out there, just waiting to be observed. And I think it’s going to lead to a renaissance of doing gravitational wave science across all scales.”
Katelin is not the only one who sees a renaissance coming. Hertz Fellow and professor of astronomy, Alex Filippenko, from Berkeley says that, “The LIGO detection of gravitational waves is a magnificent achievement. It confirms a major prediction of Einstein's general theory of relativity and opens a whole new window for observing the universe. Already, an interesting and somewhat unexpected system was discovered –-- the merger of two roughly 30-solar-mass black holes. Who knows what other fascinating objects will be found in the future?”
As a theoretical cosmologist, Schutz studies the universe, how it began, and what it’s made of, and uses that knowledge to understand exotic and fundamental physics. Throughout her academic career at MIT and Berkeley, she’s conducted research in areas such as the origins of the Big Bang, the particle nature of dark matter, primordial black holes, and an effective field theory approach for understanding the formation of structure in the universe. Currently, she’s exploring novel ways of detecting exotic dark matter, the elusive building block that makes up an estimated five-sixths of the matter in the known universe, but so far has yet to be directly observed.
“It’s sort of disturbing that we’ve known about dark matter for almost a century and yet we still don’t have any clue what it’s made of or what its properties are,” Schutz said. “It’s so ubiquitous but we don’t know what its interactions are like with the stuff we are made out of. All we know for sure is that it’s very important for helping to form galaxies via its gravitational interactions. It’s kind of like if someone invisible was in your house rearranging all your furniture, you’d want to get to the bottom of it.”
Raised in rural western New York, Schutz was always a voracious reader with an interest in math and the cosmos. At 16, when most of her peers were begging for a car, Schutz wanted a telescope. After high school, she left her small town to attend MIT, where she studied general relativity, quantum field theory, astrophysics, cosmology and particle physics of the early universe. She was awarded a Hertz Fellowship in 2014.
“Having a network of people who think in the same way that I think is so valuable,” Schutz said. “It’s just a wonderful community. It has really been what’s kept me going and motivated.”
Schutz is scheduled to earn her PhD in physics in 2019 and intends on keeping on an academic path, as a faculty member at a university or pursuing a job at a national lab such as Lawrence Berkeley, where she’s currently working with physicist Kathryn Zurek on dark matter detection.
When asked about the apparent breadth of her research, Schutz laughed. “I just really enjoy seeing the confluence of different kinds of physics coming together,” she said. “Basically I’m just doing whatever’s fun right now.”
A self-described “foodie,” Schutz also enjoys cooking and rock climbing.
To contact Hertz Fellow Katelin Schutz regarding her research: firstname.lastname@example.org