Searching for the signals of colliding neutron stars

When two neutron stars merge, a hypermassive neutron star is formed in the short term. After a maximum of 300 milliseconds, however, it collapses again and becomes a black hole. This makes it almost impossible to ever directly observe such an exotic species. A research team led by Cecilia Chirenti from the University of Maryland now describes in the journal »Nature«that it found evidence of two such events in archival data from a former NASA space telescope.

Collisions of massive objects of all kinds are usually a case for gravitational wave detectors. Since the gravitational-wave signal from two merging black holes was first revealed to the public in 2016, the gravitational-wave detector LIGO, short for Laser Interferometer Gravitational-Wave Observatory, has been able to measure dozens of such signals. However, researchers around the world were even happier about the signal GW170817 from 2017. At the same time as the gravitational wave signal, the Fermi satellite received electromagnetic signals from a gamma-ray burst. And in the days that followed, numerous other observatories were able to observe the afterglow.

What is special: At GW170817, two neutron stars merged with each other. It was not only the first time that astronomers were able to measure both gravitational waves and electromagnetic radiation from the same astronomical event. It also told them that a merger of two neutron stars can indeed produce short gamma-ray bursts – a long-held assumption. Since then has the stroke of luck of GW170817 no longer repeated, the current gravitational-wave signals lack the electromagnetic counterpart. Therefore, researchers often do not know exactly what is actually fused together.

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