The Phenomenon of Continuing to Produce X-rays After the Collision of Neutron Stars has Puzzled Astronomers

According to foreign media CNET reports, astronomers have discovered that two neutron stars collide with each other about 130 million light-years away from the earth. On August 17, 2017, the collision between some of the densest celestial bodies in the universe produced gravitational waves and X-rays. Dozens of telescopes on Earth have captured this rare merger at different wavelengths of the electromagnetic spectrum. First, there is a burst of high-energy gamma rays, followed by a burst of light and ultraviolet, radio and infrared signals.

About nine days after the collision, NASA’s Chandra Observatory received X-ray signals. According to astronomers' understanding of neutron stars, it should have disappeared by now. But in a new study published on Monday in the Journal of the Royal Astronomical Society , researchers studied the neutron star collision called GW170817 and found that after 1,000 days, X-ray signals can still be detected. "We really don't know what to expect from this point, because all our models predict that there will be no X-rays," said Eleonora Troja, an astrophysicist at NASA's Goddard Space Flight Center and lead author of the study. Said in the press release. GW170817 is the first neutron star merger detected by three gravitational wave observatories on Earth. The three major observatories were able to triangulate the location of the merger immediately after the merger occurred, allowing researchers to turn their telescopes into space to observe the event carefully.

Since no multiple neutron star collision events have been observed (so far only two have been recorded and confirmed), scientists have to rely on models to predict the consequences. In most cases, these models are consistent with the test results of GW170817. When two neutron stars collide, they will release gamma-ray jets and huge bright gas explosions, called "thousand novae." These events are short-lived-by observing them a few days or weeks later, they disappear. But when NASA’s X-ray observatory Chandra focused on the merger in February, it was still detecting X-rays at the location, two and a half years after it exploded with vitality. The latest measurement results show that the signal has faded, but the X-ray signal can still be detected. Why can these X-rays still be detected? This is a problem that researchers are trying to solve. It may be that there is an additional component in the neutron star merger, which the model did not consider before. It may also be that the dynamics of the energy released after the collision are somewhat different from what scientists expected. An exciting possibility is that the merged debris represents an X-ray neutron star - although more analysis is needed to determine the source of the signal. Astronomers will turn their telescopes to GW170817 in December to provide another opportunity to uncover the mystery of the merger. "No matter what happens, this event is changing our understanding of neutron star mergers and rewriting our model," Troja said.