The neutron star collision is 520 million light-years away

Astronomers for the second time discovered gravitational waves generated from the intense merger of two neutron stars.

The collision of two super neutron stars creates gravitational waves. Photo: CNN.

The two neutron stars in the collision are larger than any known binary star pair. Because they collided at 520 million light-years away, gravitational waves from the event now reach Earth. Astronomers announced their findings at the 235th annual meeting of the American Astronomical Society in Honolulu on January 6. The results of the study challenge the hypothesis about the process of neutron star pairs forming and merging.

On April 25, 2019, the Laser Interferometer Gravity Observatory (LIGO) in Livingston, Louisiana, received the gravitational wave signal in the universe. At first, the team did not know which event produced the gravitational wave. They wondered between the three hypotheses that were collisions between neutron stars and black holes, collisions between two super-large neutron stars or three merged black holes.

The first time researchers discovered gravitational waves generated from neutron star collisions was August 2017. It was also the first time gravitational waves, heavy metals such as gold and platinum, were observed during the same event. Because no light signals were detected during the April 2019 collision, the team identified the objects in the event as being extremely massive.

"Through observation, we know there are 17 binary neutron star systems in our galaxy and an estimate of the mass of these stars," said Ben Farr, a LIGO member at the University of Oregon. "Surprisingly, the total mass of the newly discovered binary system is much higher than expected."

Neutron stars are the smallest type in the universe, traces of supernova explosions. Their diameter is equivalent to a city like Chicago or Atlanta, but they are very dense and more massive than the Sun. According to the team, the total mass of the two neutron stars in the collision is 3.4 times larger than that of the Sun. Meanwhile, the neutron stars in the Milky Way are only about 2.9 times the size of the Sun.

Researchers do not exclude the possibility that an object in the collision is a black hole. But based on the data, they are convinced that the collision occurred between two unusually large neutron stars. Neutron-star pairs form when two super-massive stars in binary come to the end of their lifecycle. They can also form separately and merge in orbit.