Gravitational waves are back. And this time, they’re not traveling alone. In the first four detections of these astronomical phenomena, gravitational waves emanated from merging binary black holes—a source that puts off no light.
On Monday, Astronomers from LIGO, the Laser Interferometer Gravitational-Wave Observatory, and the Virgo detector in Italy announced in a press conference that they discovered a collision of neutron stars that released both a stream of gravity waves and a flash of light. These findings–published in a suite of Science and Nature papers–back decades-old theories, including one by Albert Einstein that gravitational waves travel at the speed of light.
“It’s a privilege to discover that neutron stars can also emit gravitational waves, especially so close to the original gravitational wave discovery’s second anniversary,” said Stefano Covino, a researcher at the National Institute for Astrophysics in Italy and lead author of a Nature Astronomy paper that details some of the announced findings. LIGO and Virgo identified the gravitational waves from the twin neutron stars on August 17. At about 130 million light years away, this is the nearest gravitational wave event detected so far.
Astronomers verified the source by the neutron stars’ low masses. Black holes tend to start at around three to five times the mass of our sun. The new source ranged from 1.1 to 1.6 solar masses, which fit the bill for a neutron star.
Though it doesn’t seem massive, a neutron star is the collapsed core of a giant star after it goes supernova. They’re packed with neutrons (hence the name) and are usually about 12 miles in diameter. The density of a neutron star is so great that scooping up a teaspoon of its matter would weigh more than a billion tons. So, neutron stars — like black holes — were considered by astronomers to be massive enough to interact with the universe; thus, causing gravitational ripples in the curvature of spacetime.
Neutron star mergers were what scientists initially expected to find with LIGO, explained astrophysicist France Córdova, director of the National Science Foundation, which funds LIGO.