The Universe Spoke, The World Listened (And Cheered)

Gravitational waves were detected for the first time on that day -- confirming Einstein’s general theory of relativity. And after decades of planning, testing and hard work, the Laser Interferometer Gravitational-Wave Observatory (LIGO) Scientific Collaboration uncovered the first physical evidence that black holes exist.

Northwestern astrophysicists Vicky Kalogera and Shane Larson had been working feverishly with scientists around the world since they first heard the news in September, checking data, doing multiple simulations, participating in countless teleconferences and writing a flurry of scientific papers.

The Northwestern scientists were more than ready for the media rollout last week and were cited in a number of news outlets, including The New York Times, The Washington Post, The New Yorker, the Chicago Tribune, and several local broadcast outlets.

The following is an excerpt from the The New York Times story, in which Kalogera shares her expertise in black-hole formation in binary systems and in LIGO data analysis.

A team of scientists announced on Thursday that they had heard and recorded the sound of two black holes colliding a billion light-years away, a fleeting chirp that fulfilled the last prediction of Einstein’s general theory of relativity.

That faint rising tone, physicists say, is the first direct evidence of gravitational waves, the ripples in the fabric of space-time that Einstein predicted a century ago. (Listen to it here.) It completes his vision of a universe in which space and time are interwoven and dynamic, able to stretch, shrink and jiggle. And it is a ringing confirmation of the nature of black holes, the bottomless gravitational pits from which not even light can escape, which were the most foreboding (and unwelcome) part of his theory.

More generally, it means that a century of innovation, testing, questioning and plain hard work after Einstein imagined it on paper, scientists have finally tapped into the deepest register of physical reality, where the weirdest and wildest implications of Einstein’s universe become manifest.

Conveyed by these gravitational waves, power 50 times greater than the output of all the stars in the universe combined vibrated a pair of L-shaped antennas in Washington State and Louisiana known as LIGO on Sept. 14.

If replicated by future experiments, that simple chirp, which rose to the note of middle C before abruptly stopping, seems destined to take its place among the great sound bites of science, ranking with Alexander Graham Bell’s “Mr. Watson — come here” and Sputnik’s first beeps from orbit.

Later in the Times story, Kalogera discussed the size of the two binary black holes that merged to form the bigger, gravitational wave-producing black hole:

Astronomers now know that pairs of black holes do exist in the universe, and they are rushing to explain how they got so big. According to Vicky Kalogera of Northwestern University, there are two contenders right now: Earlier in the universe, stars lacking elements heavier than helium could have grown to galumphing sizes and then collapsed straight into black holes without the fireworks of a supernova explosion, the method by which other stars say goodbye. Or it could be that in the dense gatherings of stars known as globular clusters, black holes sink to the center and merge.  

Kalogera is one of LIGO’s most senior astrophysicists and led the LIGO effort as the LIGO co-editor of the paper about the discovery’s implications. At Northwestern, she is director of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). She also is the Erastus O. Haven Professor of Physics and Astronomy and associate chair of the physics and astronomy department in the Weinberg College of Arts and Sciences.

“I often daydreamt about announcing our discovery to the world, but I could never imagine or anticipate the excitement with which the public and our science colleagues have received this ‘historic,’ as they call it, discovery,” Kalogera said, reacting to the media coverage.

“At Princeton last week, I was asked to pose for a photo shoot in front of Einstein’s desk, and later I got a call from Greece’s president. Whirlwind does not come close to describing this experience! Almost as dizzying as riding the waves we discovered! 

Kalogera, a native of Greece, leads the LIGO research team at Northwestern, which currently includes Larson, two postdoctoral fellows, three graduate students and several undergraduate students. The team’s contributions to the Sept. 14 discovery include making predictions for anticipated detections, interpreting the astrophysics, analyzing the data and characterizing the detectors.

Larson is a research associate professor of physics and astronomy at Northwestern, a CIERA member and an astronomer at the Adler Planetarium in Chicago. He has been involved with LIGO for five years and with the gravitational-wave community for more than a decade.

Reflecting on the announcement, Larson said, “Today has been an amazing day! And while I have spent my whole scientific career working on gravitational waves, there are many in our field who have spent far more time on this. The opening moment of the press conference will be burned in my mind forever -- Dave Reitze nailed it: ‘Ladies and gentlemen -- we have discovered gravitational waves. We did it!’”

Another Northwestern colleague, Selim Shahriar, who is not an astrophysicist but an electrical engineer in The McCormick School Engineering and Applied Science, focuses on the laser physics of this enterprise.