After nearly a century, the hunt for an elusive cosmic quarry is over. With the help of lasers and mirrors, scientists have directly observed gravitational waves, or wrinkles in the fabric of spacetime itself.
Two colliding black holes, one with 36 times the mass of the sun, and the other with 29, emitted those gravitational waves as they spiralled into one another and eventually collided.
From roughly 1.3 billion light-years away, these waves spread like ripples in the cosmic pond and washed over Earth on September 14, causing a minuscule but measurable change in the distance between four sets of mirrors—two in Louisiana, and two in Washington state.
In the last second before the black holes merged, they released 50 times more energy than all the stars in all the galaxies in the universe were releasing, combined.
“It’s the first time the universe has spoken to us in gravitational waves,” said David Reitze of Caltech during a press conference announcing the discovery on February 11.
To scientists monitoring that mirror-based experiment at the Laser Interferometer Gravitational-wave Observatory (LIGO), the signal received on Earth carried the characteristic “chirp” predicted to accompany the death and unification of two black holes.
“We can hear gravitational waves, we can hear the universe,” said Gabriela Gonzalez of Louisiana State University. “We are not only going to be seeing the universe, we are going to be listening to it.”
It’s a discovery that many say is likely to earn a Nobel Prize, and an announcement that has been hinted at for weeks, if not months, as tantalizing rumors of the LIGO team’s find circulated on social media.
First predicted by Einstein in 1916, gravitational waves are among the most paradoxical parts of his theory of general relativity. They’re produced by extreme events—such as colliding black holes, merging neutron stars, or exploding stars—that are energetic and violent enough to warp the tough, stiff fabric of spacetime, causing it to expand and contract.
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