An international research collaboration has detected a mystery object inside the puzzling area known as the “mass gap” — the range that lies between the heaviest known neutron star and the lightest known black hole, according to a new study published on Tuesday.
When the most massive stars die, they collapse under their own gravity and leave behind black holes. When stars that are a bit less massive than this die, they explode in a supernova and leave behind dense, dead remnants of stars called neutron stars.
The heaviest known neutron star is no more than 2.5 times the mass of the sun, or 2.5 solar masses, and the lightest known black hole is about five solar masses, according to the study.
For decades, astronomers have wondered if there are any objects in this mass gap. In the new study from the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European Virgo observatory, scientists have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap.
The intriguing object was found on August 14, 2019, as it merged with a black hole of 23 solar masses, generating a splash of gravitational waves detected back on earth by LIGO and Virgo, according to the study published in The Astrophysical Journal Letters.
“Mergers of a mixed nature — black holes and neutron stars — have been predicted for decades, but this compact object in the mass gap is a complete surprise,” said Vicky Kalogera of Northwestern University, who coordinated writing of the paper.
“We are really pushing our knowledge of low-mass compact objects. Even though we can’t classify the object with conviction, we have seen either the heaviest known neutron star or the lightest known black hole. Either way, it breaks a record,” she said.
The finding has important implications for astrophysics and the understanding of low-mass compact objects, according to the study.