Explosive neutron star collision is still emitting X-rays, puzzling astronomers

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


When two neutron stars smashed into each other, about 130 million light-years from Earth, the universe lit up. The collision, between a number 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 alerts.

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

However in a brand new examine, revealed 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,” stated 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 a great take a look at the occasion. And it is a violent one.

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As a result of we have not seen many neutron star collisions (solely two have been recorded and confirmed up to now), 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 shiny fuel, often known as a “kilonova.” These occasions are transient — we see them for a couple of days or perhaps 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 targeted on the merger in February, two and a half years after it flared to life. The most recent measurements present the sign has light, however the specter of an X-ray burst continues to be seen and it is somewhat brighter than fashions predicted. Why are these X-rays nonetheless seen? That is a puzzle the researchers try to resolve.

It could be there’s an extra 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 somewhat completely different to what we anticipate. An thrilling chance is that the stays of the merger symbolize 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,” stated Troja.

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Jackson Ryan