For the first time ever, humans have observed light and gravitational waves from the same event, a neutron star collision 130 million light years away. Thanks to advance warning from the Laser Interferometer Gravitational-Wave Observatory (LIGO), roughly 70 observatories from every continent on Earth, including Antarctica, managed to tune in to watch the merger.
Based on this first-ever “multi-messenger” event, thousands of scientists are now making breakthroughs about the behavior of neutron stars and the origin of elements like gold and uranium.When enormously heavy objects, such as black holes, smash into each other, they release enough energy to deform the fabric of spacetime, the same way tossing a stone into a pool of water can produce ripples. The twin LIGO detectors in Hanford, Washington and Livingston, Louisiana, which keep watch for these wave signals, have already detected several black hole collisions, an achievement worthy of this year’s Nobel Prize. Most recently, Italy’s Virgo detector also began picking up gravitational waves.
On August 17, LIGO received a signal, dubbed GW170817, unlike any it had detected before. Researchers published the full results in Physical Review Letters. While the black hole mergers had produced brief chirps in limited sets of frequencies, this signal lasted 100 seconds and spread through the entire frequency range. Scientists realized the objects that had produced GW170817 were much smaller than black holes—they had to be neutron stars.
What’s a neutron star?
A neutron star weighs slightly more than our Sun, but crams that mass into an object fewer than 12 miles (less than the length of Manhattan) across. Because they’re so incredibly dense—one teaspoon of neutron star would weigh about six billion tons—the matter in these stars doesn’t look like the familiar atoms that make up all the stuff on Earth. Instead, neutron stars contain the particles you’d normally find in an atom’s nucleus, a densely-packed crowd of neutrons (hence the name) with a smattering of protons mixed in.
Unlike black holes, neutron stars create a visible spectacle when they collide: Theorists have predicted that they would shoot out jets of gamma rays and hurl glowing matter into space. So when LIGO heard GW170817, its researchers alerted astronomers all over the globe to start scanning the skies. Thanks to Virgo, they could also tell observatories roughly where to look. The signal that reached each detector had a slightly different strength and arrived at a slightly different time, and researchers could analyze these disparities to narrow down the area of space where the waves must have originated: a 30-square-degree region visible from Earth’s southern hemisphere.
NASA’s Fermi Space Telescope picked up a tell-tale burst of gamma rays. Optical telescopes in Chile caught the merger spewing jets of molten matter, allowing researchers to pinpoint the exact galaxy where the neutron stars had collided: NGC4993. X-ray telescopes, radio telescopes, infrared and ultraviolet telescopes, even a neutrino detector at the South Pole—just about every observatory that could view the southern hemisphere tried to catch sight of this merger.
“There’s probably never been an event so closely monitored by so many telescopes,” Columbia University astrophysicist Brian Metzger told Popular Science.
That wide variety of eyes on the sky fulfills one of the most valuable promises of gravitational wave astronomy: multi-messenger events. By watching the neutron-star merger through gravitational waves, gamma rays, and the full electromagnetic spectrum, researchers are already making breakthroughs about how neutron stars, as well as many of the elements in the universe, formed. As they continue to analyze their data, more papers are sure to follow.
“We’re just beginning to explore the gravitational universe,” David Reitze, executive director of the LIGO Laboratory at Caltech, told Popular Science. “It’s very likely that we’re going to see something that no one anticipated, that really shakes the paradigms of established scientific theory.” (Reitze’s number-one goal: “Proving Einstein wrong, with all due respect, would be a big deal. We might be…
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