Gabriela González is an undercover celebrity.
Soft-spoken, humble and always smiling, you’d never guess from passing Gaby on LSU’s campus that she’s one of the biggest names in gravitational wave research. Just a little over two years ago, scientists at LIGO (Laser Interferometer Gravitational-Wave Observatory) observed ripples in the fabric of spacetime, called gravitational waves, for the first time. Today, the pioneering leaders of LIGO have been awarded the 2017 Nobel Prize in Physics for the detection of those ripples in spacetime. Gaby, a professor of physics and astronomy at LSU, has been and continues to be instrumental in testing and improving the sensitivity of LIGO detectors to tell us when gravitational waves from distant astronomical events such as the collision of black holes are passing by earth.
In 2015, Gaby became the first spokesperson of the LIGO Scientific Collaboration (LSC) to announce the groundbreaking detection of gravitational waves. These “waves” produce tiny movements within detectors that live inside the long arms of LIGO Livingston in Louisiana and LIGO Hanford in Washington.
With her propensity for big ideas and inspirational words, Gaby is also the kind of scientist that other scientists want at their birthday parties. Even Stephen Hawking couldn’t pass up the opportunity to invite Gaby to his 75th!
Gaby traveled to Cambridge, U.K. for the event, to not only celebrate Hawking’s birthday but to talk about LIGO’s discovery of gravitational waves. As Gaby walked through the halls of the University of Cambridge, she felt like she was walking into the world of Harry Potter, she laughed.
It was the first time Gaby had seen Hawking in person. “I was a bit nervous,” Gaby laughed. “I was so impressed that to celebrate his birthday, instead of a cruise or vacation, he asked for a scientific symposium. When I got there, I realized that there were only four speakers presenting at the public symposium, and they were all very famous! Well, three of them were famous – the fourth was me!”
Hawking’s birthday celebration speakers included himself, famous British science communicator Brian Cox, Gabriela González, and Lord Martin John Rees, a British cosmologist and astrophysicist who has a long history of working with Hawking.
“Hawking is famous for many things, but one of the things he is famous for is his work on the area theorem of black holes, which says that when two black holes collide to form a larger black hole, the area of the larger black hole is greater than the sum of the individual areas of the smaller black holes,” Gaby said. “This theorem isn’t trivial, and has to do with the theory of the thermodynamics of black holes that was developed after Hawking proved black holes can evaporate.”
Soon after LIGO first announced the discovery of gravitational waves emanating from a black hole merger, there were questions about whether the discovery could prove his area theorem. Unfortunately, Gaby says, scientists can’t prove this theorem from the first LIGO detection because they didn’t have the precision to deduce the area of the final black hole independently of the areas of the smaller black holes.
“I knew Hawking was curious about this, and would want to hear about it in my talk at his symposium. I was nervous about that,” Gaby laughed. “I tried my best to explain our discovery and how it relates to Hawking’s work on black holes.”
Gaby was touched and a bit relieved, she laughed, that in Hawking’s symposium speech that followed hers, he discussed not only his own life in physics but also how excited he was to see the detection of gravitational waves.
“Hearing Hawking talk left a big impression on me,” Gaby said. “Not just because I heard him mention my name, pronounced by his machine, but because I could tell how difficult life is for him, and yet he had not only asked for this event to be organized but had been there all day and prepared multiple talks, including one on the spot between the public symposium and dinner. I developed such an admiration for his courage and active interest in science at 75 years old. It was amazing.”
Much More than a Theory
Many people don’t know that Hawking developed an interest in the experimental study of gravitational waves in the 1970s, before interferometers like those at LIGO observatories were developed to do just this. In his book My Brief History published in 2013, Hawking wrote about his early interest in gravitational waves, and about how he later abandoned the pursuit of their detection when it seemed that it was practically impossible to build detectors sensitive enough. “I am very glad I remained a theorist,” Hawking wrote in 2013.
“Gravitational wave detectors have become much more sensitive since the 1970s. The current detectors employ laser ranging to compare the lengths of two arms at right angles. The U.S. has two of these LIGO detectors. Although they are ten million times more sensitive than [the ones Hawking had suggested building], they have not so far made a reliable detection of gravitational waves. I’m very glad I remained a theorist.” – Stephen Hawking, My Brief History, 2013
“I told him [Hawking] that I was very glad he remained a theorist, too, because he has accomplished great things as a theorist,” Gaby laughed. “But we have detected them now!” Gaby left dinner with Hawking’s autograph, his thumbprint, in a copy of his book, within the chapter on gravitational waves.
Gaby’s research group continues to be very involved in improving the sensitivity of the LIGO detectors, as well as in the instrumental characterization and calibration of data collected in the data-taking Observing Runs performed by the LIGO Scientific Collaboration (LSC). She has published several early papers on the specific predictions of Brownian motion as a limiting source to the detectors' sensitivity. She was a founding member of LSC and has participated intensely in the commissioning of the LIGO detector at the Livingston Observatory since joining LSU in 2001, in issues related to alignment sensing and control. Now that LSC has a new spokesperson, Gaby is excited to move back into her role as a researcher at LIGO and a teacher. She has missed these roles, especially teaching, over the last few years as her duties as the LSC spokesperson demanded much of her time and energy, even though public speaking has quickly become one of Gaby’s passions.
“It’s such an exciting time for research now at LIGO,” Gaby said. “Before the detection of gravitational waves, it was always a pleasure but also a challenge to work with the instrument to overcome the limitations we thought might be preventing reliable detections. But now we know that with every little bit we improve the sensitivity of the LIGO detectors, we are going to see more and more things, not just black holes, but all kinds of astronomical events. Now, there is even more gratification in working with the instrument.”
Gaby’s next steps include further improving LIGO detection sensitivity and conceptualizing and potentially developing and building third-generation facilities to detect gravitational waves. As of September, 2017, the LSC has announced four detections of gravitational waves from binary black hole systems, and looks to soon detect other events, such as coalescence of binary neutron star systems, rotating stars in our Galaxy, and most exciting of all, the unknown.