For many years astronomers have wondered about a gap that lies between a neutron star and black holes. The heaviest known neutron star is no more than 2.5 times the mass of the sun, and the lightest known black hole is about five solar masses. The mystery for scientists is what exactly lies in the so-called mass gap between those two objects. A new study from the LIGO and Virgo detectors has discovered an object that is 2.6 solar masses putting it firmly in the mass gap that has puzzled scientists for so many years.
The object was discovered on August 14, 2019, as it merged with the black hole of 23 solar masses. That merger generated gravitational waves detected on Earth by LIGO and Virgo. The scientists say that they don’t know if the object is the heaviest known neutron star or the lightest known black hole. Either way, the object sets a record.
Researchers say that the discovery will change how scientists talk about neutron stars and black holes. They believe that the mass gap may not exist at all and could have been due to limitations in observational capabilities. Researchers say more time and observations will help settle that argument. The event detailed in the study was dubbed GW190814. The merger resulted in a final black hole about 25 times the mass of the sun.
Some of the merged mass was converted to a blast of energy in the form of gravitational waves. Researchers note that the newly formed black hole is about 800 million light-years from Earth. Before the two objects merged, their masses different by a factor of nine, making this the most extreme mass ratio known for a gravitational-wave event.
When scientists discovered the merger, they did send out an alert to the astronomical community, and dozens of ground and space-based telescopes searched for light waves generated by the event, but none were picked up. Light counterparts to gravitational-wave signals have been seen only once. Black hole mergers, in most situations, are believed to produce no light.