Colliding two neutrons produce stars, gravitational waves and a huge, bright jet.
Caltech / LIGO
When Two neutron stars crashed into each other, About 130 million light-years from Earth, the universe was illuminated. Dozens of telescopes on Earth received a rare merger in various wavelengths of the electromagnetic spectrum on August 17, 2017, as this collision between some of the densest objects in the universe spreads gravitational waves and fireworks. First, there was an explosion of very intense gamma rays, followed by an explosion of light and UV, radio and infrared signals.
About nine days after the collision, NASA’s Lunar Observatory Scored an X-ray signal. According to our understanding of neutron stars, it should now be gone.
But in a new study published Monday in the Royal Astronomical Society’s journal Monthly Notices, researchers studied the neutron-star-on-neutron-star effect, designated GW170817 and found that 1,000 days later, the X-ray signal was still Detectable.
“We don’t really know what to expect beyond this point, because all of our model models were predicting an X-ray,” said Eleanora Troja, an astrophysicist and lead author on the study at NASA’s Gaddard Space Flight Center, in a press release. .
GW170817 is the first neutron star merger to be discovered by three gravitational wave observatories located on Earth. The triad of observers was able to triangle the moments of the merger after it happened, allowing researchers to rotate their telescopes into space and get a better view of the event. And it’s violent.
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Because we haven’t seen many neutron star collisions (so far only two have been recorded and confirmed), scientists have relied on models to predict the outcome. Mostly, the models stood in line with what was found with the GW170817. When two neutron stars collide, they emit a jet of gamma rays and a large explosion of luminous gas, known as “kilonova.” Those events are fleeting – we’ll see them for a few days or weeks and then they’ll disappear. That was the case with GW170817.
But at NASA’s X-ray observatory, Chandra was still searching for X-rays at the site, when he was focusing on a merger in February, a year after it exploded in life. The latest measurements show that the signal has disappeared, but the spectrum of the X-ray explosion is still visible and is slightly brighter than the predicted models. Why do these X-rays still appear? It is a puzzle that researchers are trying to solve.
It may be that the neutron star merger is an additional component that is not in the previous calculations of the models. Or perhaps the dynamics of energy released after a collision are slightly different from what we expect. One compelling possibility is that the merger remnants represent a neutron star rather than X-ray-emission – although further analysis is needed to determine where the signal comes from. In December astronomers will turn their telescopes toward GW170817, offering a second chance to unravel the mystery at the merger.
“Whatever happens, this event is changing what we know about the Neutron Star merger and could rewrite our models,” Troza said.
