Astronomers now say they’ve heard a second refrain of a cosmic disco beat — the echoes of two more crashing black holes.
This latest discovery by the same team that shook the world of astrophysics when it first detected such a gravitational wave last year hints that the unseen violence of the universe might actually be pretty common.
A gravitational wave is the warp in the fabric of the cosmos that Albert Einstein predicted a century ago in his theory of general relativity, something that results only from the most massive space crashes. It’s something that can’t be seen and that Einstein thought would never be detected.
But an international team of scientists that includes researchers at Northwestern University, Adler Planetarium and the University of Chicago have found a way to hear it — first one note, in September, and now two.
“This is what we call gravity’s music,” said Louisiana State University physicist Gabriela Gonzalez, scientific spokeswoman for the discovery team.
Gonzalez made the announcement at a news conference at the summer meeting of the American Astronomical Society in San Diego where the sounds from the two gravitational waves were played.
With that second, higher-pitched chirp — which was detected Christmas night in the United States — the scientists have switched from reveling in the “aha” of first discovery to the more detailed and telling recording of the historical soundtrack of a chaotic universe. They likened that soundtrack to jazz, maybe with a mix of classical music.
Scientists first heard the cosmic crash after turning on their $1.1 billion set of twin instruments known as the Laser Interferometer Gravitational-wave Observatory, or LIGO. But they weren’t certain then whether they’d lucked into a once-in-a-lifetime chirp from a rare event or if these gravitational waves have been out there waiting to be listened to on a regular basis.
“This event really does establish that there are quite a few merging black holes in the nearby universe,” said Penn State University physicist Chad Hanna, one of the more than 1,000 scientists who wrote the study, released Wednesday at the astronomers conference and published in the journal Physical Review Letters. “The universe is full of these tremendous collisions that are depositing tremendous energy.”
It’s the type of crash that might happen in our own Milky Way once every few hundred millions of years or so, but, by looking at so many other galaxies, we can hear more, said Barnard College physicist Janna Levin, author of “Black Hole Blues And Other Songs From Outer Space,” who wasn’t part of the study.
Columbia University astrophysicist Szabolcs Marka, a member of the discovery team, said detecting the first wave was like going outside and finding a $100 bill. Finding a second one so soon tells scientists that this is more likely to be a regular windfall. He said he wouldn’t be surprised if, once they upgrade their equipment, scientists hear a gravitational wave about once a week.
“They were never rare,” Gonzalez said, but were hard to hear until scientists, in effect, got the right hearing aid.
The latest sound was from a cosmic crash 1.4 billion light-years away. One light-year is 5.9 trillion miles.
The first black hole crash that scientists heard in September was from two massive objects that were unusually huge even for black holes. December’s black holes were more normal-sized — 14 and eight times the mass of our sun. Those mergers produce faint invisible ripples in the fabric of the cosmos that bunch up like a kink in a net.
None of that can be seen. The wave is noticed on Earth only in incredibly tiny misalignments of split laser beams in detectors in Hanford, Washington, and Livingston, Louisiana. That mismatch is a vibration that scientists can hear as sound.
The Christmas Day wave was fainter but lasted longer, Gonzalez said — one second, vs. one-fifth of a second for the earlier one. Marka called it a crescendo. Levin likened it to a drumbeat or whale’s song.