Astronomers detect gravitational waves from a merged, hyper-massive neutron star

Gravitational waves become extremely weak by the time they reach the Earth and require highly sensitive equipment for detection

Two astronomers claim to have detected gravitational waves from a merged hyper-massive neutron star. This is the first time that gravitational waves from a merged hyper-massive neutron star have been observed by any research team.

Gravitational waves are hard to detect as they become extremely weak by the time they reach Earth. To detect these waves, highly sensitive equipment is required, like the Laser Interferometer Gravitational Wave Observatory (LIGO) detector, which has enabled scientists to observe gravitational waves for the first time in 2016.

Since 2016, scientists have succeeded in detecting these waves on only six other occasions.

In August 2017, astronomers detected a gravitational wave signal resulting from the coalescence of two neutron stars. The signal was detected by both, the LIGO and Virgo detectors. The LIGO detection event was named GW170817 by scientists.

This signal had duration of only about 100 seconds, exhibiting the characteristics expected of the inspiral - merger - of two neutron stars.

Analysis of the data further indicated that the two neutron stars likely merged into a black hole.

In the latest study, Massimo della Valle of the Osservatorio Astronomico de Capodimonte in Italy and Maurice van Putten of Sejong University in South Korea decided to confirm the previous result using the data from LIGO and the Virgo gravitational wave detector in Italy.

LIGO data revealed that the H1 and L1 detectors (located about 3,000 kilometres apart from each other) had also simultaneously detected a descending 'chirp' that lasted for about 5 seconds. The frequency of that chirp was less than 1 KHz, which further reduced to 49 Hz.

The chirp started between the end of the opening burst of gravitational waves and a following burst of gamma rays. These observations suggested that two neutron stars had actually merged to create a hyper-massive neutron star (instead of merging with a black hole as originally believed).

"We're still very much in the pioneering era of gravitational wave astronomy. So it pays to look at data in detail," said Van Putten. "For us this really paid off, and we've been able to confirm that two neutron stars merged to form a larger one."

The findings of the study are published in Monthly Notices of the Royal Astronomical Society: Letters.

^{The gravitational wave spectrum. Source: NASA Goddard Space Flight Center}

^{Main image: Simulating eXtreme Spacetimes. Collaboration/Canadian Institute for Theoretical Astrophysics/SciNet}