LIGO Just Detected A Second Neutron Star Collision

An artist's impression of the jet and fireball produced by the collision of two neutron stars, the second of which has now been detected. LSC/Sonoma State

When gravitational wave detectors first picked up a collision between neutron stars it was one of the scientific achievements of the century. Shortly after, the detectors were taken offline in the hope of making them more sensitive. In the first month after their restart, a second such event has been found, and soon such discoveries may be routine. Given the astonishing wealth of knowledge we gained from the first collision, this is exciting news for astronomy's future.

The first neutron star collision allowed astronomers to search the sky with optical and radio telescopes and catch the burst of light released by the encounter. This produced an unprecedented bounty of scientific papers; perhaps most importantly including the discovery that many of the universe's heavy elements, previously thought to come from supernovae, are formed in collisions like these.

Sadly, there will be no such scientific cornucopia this time. By chance, the event occurred while one of the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors was offline. “The more detectors we have, the smaller the piece of sky we can narrow an event’s location down to,” Professor Susan Scott of the Australian National University told IFLScience. Missing one detector left optical astronomers searching a quarter of the heavens. Unsurprisingly they could not find the needle of the collision's glow in that enormous haystack.

Disappointing as that is, Scott explained the discovery still bodes well for the future. Based on the small number of events we had found previously, and the approximate doubling of LIGO's sensitivity, it was anticipated we would detect roughly a black hole collision every week, and one between neutron stars every month. However, these estimates were very rough, and no one could be sure they weren’t optimistic. So far, Scott told IFLScience, things are going to plan. Hopefully next time all detectors will be in operation.

“We expect to detect gravitational waves from lots more cataclysmic events – including those we’ve never detected before such as a black hole swallowing a neutron star and nearby exploding stars, which produce much fainter signals,” Scott said in a statement.

Although we will probably never know all that much about this event, it is thought to have occurred at a distance of about 500 million light-years, four times further from us than the first one. Unlike last time, where the event was kept from the public until a slew of papers had been peer-reviewed, this one was announced within a week of detection, before papers have even been written. Scott explained to IFLScience LIGO detections are now announced online as soon as they are made, so it's hard to keep things quiet.

Many components went into the increased sensitivity, including the use of “quantum squeezers” that damp down quantum noise that would otherwise overwhelm gravitational wave signals.

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