Stony Brook Researchers Among Physicists Worldwide Celebrating 10th Anniversary of Direct Detection of Gravitational Waves

A Stony Brook University associate professor and graduate student have been part of a worldwide team of researchers who have used the loudest black hole merger detected to date to help identify how black holes work, confirming theoretical predictions about black hole spacetimes.

This revelation comes 10 years after scientists first detected ripples in the fabric of space-time, called gravitational waves, from the collision of two black holes. This latest discovery was the result of improved technology, instruments and techniques over the past decade and confirms theories predicted by Albert Einstein, Stephen Hawking and Roy Kerr.

Will Farr, associate professor in the College of Arts and Sciences Department of Physics and Astronomy, and graduate student Nicole Khusid are among the researchers around the world - as part of the LIGO-Virgo-KAGRA (LVK) collaboration, associated with the Laser Interferometer Gravitational-Wave Observatory (LIGO), the Virgo Interferometer, and the Kamioka Gravitational Wave Detector (KAGRA) - who have collaborated on this research. These results were published in a paper September 10 in Physical Review Letters.

The new analysis of data collected by LIGO was performed in part by Farr, and astrophysicist and Columbia University's Maximiliano Isi, who are both also researchers with the Flatiron Institute's Center for Computational Astrophysics. Joining them was Khusid, who worked to help detect and reveal insights into the properties of black holes and the fundamental nature of space-time, hinting at how quantum physics and Albert Einstein's general relativity theory fit together, and confirming theories first developed by Stephen Hawking about the behavior of black hole event horizons. Khusid helped develop and employed computer codes providing early analysis that helped drive the research collaborations to recognize the significance of the event.

These findings have provided the clearest measurements of a black hole merger ever taken by LIGO. The gravitational waves from this merger reveal that a 34 solar mass black hole merged with a 32 solar mass black hole, producing a 63 solar mass black hole, about the size of Long Island, spinning at 100 revolutions per second.

The team got a complete look at the collision from when the black holes first careened into each other to the final reverberations as the merged black hole settled into its new state, which happens only milliseconds after first contact. By measuring the early phases of the collision, they were able to measure the area of the progenitor black holes' horizons; and by measuring the late phases of the relaxation of the remnant, they were able to measure the area of the remnant's horizon. Hawking's theory states that the remnant's area must be larger than the sum of the progenitors' areas, and this observation matches that to extremely high statistical significance.

"Observing the gravitational waves emitted by these black holes is our best hope for learning about the properties of the extreme spacetimes they produce," said Farr. "As we build more and better gravitational wave detectors, the precision will continue to improve; but it is amazing to think that only ten years after the very first observations of a merger like this, we are already making precision measurements of the spacetime generated by these extreme objects, and able to observationally confirm precise mathematical predictions about black holes."

"Back in March, I had the opportunity to share my preliminary analyses of this 10-year-anniversary event with members of the LVK at a collaboration-wide meeting," said Khusid. "The results, namely the precise measurement of multiple tones at late times in the post-merger gravitational wave signal, quickly generated interest. It felt exciting and rewarding to hear the community respond to the science potential of this merger. With this event alone, we've performed some of the strongest tests of our understanding of gravity and black holes!"

"The improvements in sensitivity of LIGO have truly opened up a new way to see the universe," said Barry Barish, Nobel laureate and President's Distinguished Endowed Chair in Physics in the Department of Physics and Astronomy. "We now observe new events weekly, and with precision, enabling such exciting, detailed studies of black holes."

Barish, who became principal investigator and director of LIGO in 1994, orchestrated the construction and commissioning of LIGO's interferometers, leading to the historic detection of gravitational waves in 2015, validating Einstein's predictions and revolutionizing astrophysics. He and colleagues Rainer ("Rai") Weiss and Kip Thorne received the 2017 Nobel Prize in Physics "for decisive contributions to the LIGO detector and the observation of gravitational waves."

It is thought that likely future black hole merger detections will only unveil more about the nature of these objects. In the next decade, detectors are expected to become 10 times more sensitive than today, allowing for more rigorous tests of black hole characteristics.