When stars of a certain mass explode as supernovae, they leave behind an extremely dense core, or neutron star. Often, they form binary star systems that slowly merge until they become a black hole or a new neutron star. What exactly – depends on the total mass of objects.

According to computer simulations, certain regularities, called quasi-periodic oscillations, occur in gravitational waves during the formation of supernova neutron stars. Although modern instruments are not sensitive enough to detect them, a group of American astronomers has tried to detect them in gamma rays.

To do this, they combed through archival data of 700 short gamma-ray bursts recorded by three observatories over the past few decades. And they discovered these quasi-periodic oscillations on two events in July 1991 and November 1993.

Results of the research

Calculations showed that the superheavy neutron stars that were the source of these signals must be more than 2.5 times the mass of the Sun. But they didn’t exist for more than 300 milliseconds and then they turned into black holes. Additionally, they were spinning extremely fast—almost 78,000 revolutions per minute if they had that minute. For comparison, the fastest pulsar rotates at less than 43,000 revolutions per minute.

The researchers believe that future gravitational wave detectors should be sensitive enough to directly detect signatures of supermassive neutron stars. This will help to learn more about objects with such a short lifespan.