In 2017, gravitational waves and light were observed coming from the merger of a pair of neutron stars. The discovery proved that gravitational wave sources could also be viewed at visible, X-ray, and even gamma-ray wavelengths, but has remained the only such event observed to date. Now, researchers have identified a “cosmic look-alike” — an event they believe came from the same type of system as the one that produced the gravitational waves.
Such a discovery would double the number of known events of this type. “It’s a big step to go from one detected object to two,” said Eleonora Troja of NASA’s Goddard Space Flight Center, and lead author of the study published October 16 in Nature Communications, in a press release. The paper focuses on a gamma-ray burst, called GRB 150101B, seen by NASA’s Neil Gehrels Swift Observatory in 2015. Troja’s team followed up using NASA’s Chandra X-ray Observatory, Fermi Gamma-ray Space Telescope, Hubble Space Telescope, and the Discovery Channel Telescope to determine that GRB 150101B appears similar to the 2017 gravitational wave event GW170817, which was produced by a kilonova that occurred when two inspiralling neutron stars collided. Shortly after that event’s gravitational waves reached Earth, astronomers also spotted a gamma-ray burst and light at several wavelengths associated with the merger, proving that neutron star mergers are capable of producing all these signals.
During a neutron star merger, astronomers believe a narrow jet of high-energy particles is created, which is responsible for the short burst of gamma rays spotted from Earth. In the case of both GW170817 and GRB 150101B, that jet was likely viewed off-axis, meaning it was not directly pointed toward our planet, because the bursts were fainter and shorter lived than expected. Both events also generated bright blue light at visible wavelengths (the kilonova) and lasting X-ray emission. The two even came from host galaxies that look similar: old elliptical galaxies with no newly forming stars.
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