The LIGO collaboration has announced the detection of gravitational waves from a pair of neutron stars colliding. This marks just the second time ever that this kind of event has been spotted, as the smash-up sent ripples through spacetime itself.
Gravitational waves have been detected several dozen times since 2015. They come from gigantic collisions that create enough energy to warp the very fabric of spacetime. As these ripples pass over Earth, detectors like LIGO and Virgo can pick them up and pinpoint their point of origin.
Most of the detections made so far have been from pairs of black holes merging, but scientists have also observed black holes slurping up neutron stars, and in one case two neutron stars crashing into each other. And now, a second event of this lattermost type has been spotted.
In August 2017, astronomers detected gravitational waves using the two LIGO facilities in the US and Virgo in Italy. After tracing them back to their source, other telescopes and observatories around the world were trained on that spot and were treated to a stellar show of electromagnetic signals like light, radio waves, X-rays and gamma rays. That makes it the first case of “multi-messenger astronomy.”
This latest detection, which took place in April 2019, sadly wasn’t accompanied by any other signals, but it does add to our understanding of gravitational waves.
"We have detected a second event consistent with a binary neutron star system and this is an important confirmation of the August 2017 event that marked an exciting new beginning for multi-messenger astronomy two years ago," says Jo van den Brand, an author of the study.
Interestingly, this detection was made by just one gravitational wave detector – LIGO Livingston. Its partner facility, LIGO Hanford, was offline at the time, and the signal was too faint for Virgo to pick up. It normally takes several facilities to triangulate the position of a signal, but in this case the team was able to use the non-detection to infer the rough direction it came from – a patch representing about 20 percent of the sky.
There’s another oddball difference to this 2019 detection, too. The mass of the new neutron star created in the collision is far bigger than usual. It measures about 3.4 times the mass of the Sun, where as most others max out at 2.9 solar masses.
"From conventional observations with light, we already knew of 17 binary neutron star systems in our own galaxy and we have estimated the masses of these stars," says Ben Farr, an author of the study. "What's surprising is that the combined mass of this binary is much higher than what was expected.”
The research was submitted for publication in the Astrophysical Journal Letters (PDF).
Source: Caltech