Neutron star collision continues to emit X-rays, puzzling astronomers

Two neutron stars colliding, producing gravitational waves and an enormous, vivid jet.


When two neutron stars smashed into each other, about 130 million light-years from Earth, the universe lit up. The collision, between a few of the densest objects within the cosmos, produced gravitational waves and a spattering of fireworks on Aug. 17, 2017. Dozens of telescopes on Earth captured the uncommon merger across different wavelengths of the electromagnetic spectrum. First, there got here a burst of extremely energetic gamma rays, adopted by bursts of sunshine and UV, radio and infrared indicators.

About 9 days after the collision, NASA’s Chandra observatory picked up an X-ray sign. In line with our understanding of neutron stars, it ought to have pale away by now. 

However in a brand new examine, printed Monday in the journal Monthly Notices of the Royal Astronomical Society, researchers have studied the neutron-star-on-neutron-star impact, designated GW170817, and found that 1,000 days later, the X-ray sign was nonetheless detectable.

“We actually do not know what to anticipate from this level ahead, as a result of all our fashions had been predicting no X-rays,” mentioned Eleonora Troja, an astrophysicist at NASA’s Goddard House Flight Heart and lead creator on the examine, in a press launch.

GW170817 is the primary neutron star merger detected by the three gravitational wave observatories stationed on Earth. The triad of observatories had been in a position to triangulate the place of the merger moments after it occurred, permitting researchers to show their telescopes to area and get take a look at the occasion. And it is a violent one.

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As a result of we’ve not seen many neutron star collisions (solely two have been recorded and confirmed to date), scientists have needed to depend on fashions to foretell the aftermath. For essentially the most half, the fashions lined up with what was detected with GW170817. When two neutron stars collide, they launch a jet of gamma rays and an enormous blast of vivid gasoline, referred to as a “kilonova.” These occasions are transient — we see them for just a few days or even weeks after which they disappear. That was the case with GW170817.

However Chandra, NASA’s X-ray observatory, was nonetheless detecting X-rays on the location when it centered on the merger in February, two and a half years after it flared to life. The most recent measurements present the sign has pale, however the specter of an X-ray burst remains to be seen and it is a bit brighter than fashions predicted. Why are these X-rays nonetheless seen? That is a puzzle the researchers try to resolve.

It might be there’s a further part of the neutron star mergers fashions haven’t beforehand accounted for. Or maybe the dynamics of the vitality launched within the aftermath of the collision are a bit totally different to what we count on. An thrilling chance is that the stays of the merger signify an X-ray-emitting neutron star — although rather more evaluation is required to find out the place the sign is coming from. Astronomers will flip their telescopes to GW170817 in December, presenting one other alternative to unravel the thriller within the merger.

“No matter occurs, this occasion is altering what we learn about neutron star mergers and rewriting our fashions,” mentioned Troja.

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Jackson Ryan