A group of astronomers from the University of Berkeley made a discovery of a stellar ghost (an isolated dead star) that could constitute the first black hole discovered floating.
The phenomenon was found by observing the brightness of a more distant star as its light is distorted by the object’s strong gravitational field, hence it is called gravitational microlensing. The team, led by graduate student Casey Lam and Jessica Lu, an associate professor of astronomy, estimates the invisible compact object’s mass to be between 1.6 and 4.4 times that of the sun.
Berkeley warn that the object could be a neutron star rather than a black hole. Neutron stars are also dense, highly compact objects, but their gravity is balanced by internal neutron pressure, preventing further collapse to a black hole.
Whether it’s a black hole or a neutron star, the object is the first dark stellar remnant, a stellar “ghost,” discovered wandering the galaxy without being paired with another star.
“This is the first free-floating black hole or neutron star discovered with gravitational microlensing,” Lu said. “With microlensing, we can probe these solitary, compact objects and weigh them. I think we’ve opened a new window on these dark objects, which can’t be seen any other way.”