Author: Lisa Grossman / Source: Science News
When a pair of ultradense cores of dead stars smashed into one another, the collision shot a bright jet of charged subatomic particles through space.
Astronomers thought no such jet had made it out of the wreckage of the neutron star crash, first detected in August 2017. But new observations of the crash site using a network of radio telescopes from around the world show that a high-speed stream of particles did escape from the debris, researchers report online February 21 in Science.
The work is part of an emerging consensus among scientists that the merger actually produced a jet, and could shed light on the origins of mysterious flashes of high-energy light called short gamma-ray bursts.
According to theory, a pair of crashing neutron stars should merge into another dense object, possibly a black hole. In the process, a combination of extreme energies and magnetic fields could launch a bright jet of electrons and protons moving close to the speed of light. Researchers think that such jets are seen from afar as short gamma-ray bursts, or GRBs. But no one has ever directly observed a neutron star collision producing the bursts.
The 2017 neutron star crash — the first time scientists had directly observed such a merger — provided the first chance to test the idea, says study coauthor and astrophysicist Giancarlo Ghirlanda of the National Institute for Astrophysics in Merate, Italy. That merger was picked up when the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, and its sister experiment, Advanced Virgo, detected ripples in spacetime called gravitational waves caused by the crash.
Previous gravitational wave detections involved colliding black holes, which did not emit any observable light. But the neutron star crash glowed in every wavelength of light astronomers checked, from long radio waves to short gamma rays (SN: 11/11/17, p. 6). Those extra observations let astronomers tease out details of the crash and its aftermath.
After two neutron stars collided, a shell of debris surrounded the site of the collision. New research shows that a jet of charged particles eventually escaped that shell, spreading its energy out through space in an ever-widening cone. Because the jet isn’t aimed directly at Earth, scientists can observe its structure, including a core of light-speed particles and slower particles at the cone’s edges.
But, when scientists looked for jetlike gamma-ray emissions from the merger, they didn’t find any at first. Gamma rays were emitted after the crash, but they were much dimmer than expected from a GRB….
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