An international team of astrophysicists, including researchers at UBC, have detected the ‘extremely loud’ merger of a black hole with a mystery compact object—the most asymmetric gravitational-wave source yet observed.
GW190814, the merger of a heavy black hole with an unidentified compact object about nine times smaller, was reported today in Astrophysical Journal Letters.
“We can use gravitational waves to measure the masses of the two objects that collided to generate this signal,” says Jess McIver, a UBC physicist and member of the international LIGO Scientific Collaboration. “But it’s difficult to tell from its mass alone whether the smaller object was an incredibly light black hole, an incredibly heavy neutron star, or something else entirely.”
When stars die, they can collapse into black holes or explode in a supernova that leaves behind dense, dead remnant star cores called neutron stars. For decades, astronomers have been puzzled by the observed gap between measured neutron star masses and black hole masses. Past observations that used light to measure black hole companions orbiting stars yielded neutrons stars with masses no more than 2.5 times our own Sun, and black holes with masses no less than five times that of our Sun. The question has remained: Could any stellar remnant could form in this ‘mass gap’?
The mass of the lighter compact object in the GW190814 system lies between 2.5 and three solar masses, placing it confidently within the ‘mass gap’. This makes it heavier than nearly every neutron star observation reported to date, or an unusually light black hole, consistent only with the remnant black hole from the binary neutron star merger observed in 2017, GW170817.
“This is going to change how scientists talk about neutron stars and black holes,” says co-author Patrick Brady, a professor at the University of Wisconsin, Milwaukee, and the LIGO Scientific Collaboration spokesperson. “The mass gap may in fact not exist at all but may have been due to limitations in observational capabilities. Time and more observations will tell.”