Astronomers may have identified the Milky Way’s first free-floating black hole.
When huge stars die, they leave behind black holes, although isolated black holes are invisible.
Observing the brightness of a more distant star as its light was bent by the object’s strong gravitational field — so-called gravitational microlensing — astronomers have now uncovered what may be a free-floating black hole for the first time.
The compact object, which is estimated to be between 1.6 and 4.4 times the mass of our sun by UC Berkeley researchers, could be a free-floating black hole, one of 200 million in the Milky Way galaxy.
The researchers warn that the object could be a neutron star rather than a black hole because astronomers believe the relic of a dead star must be heavier than 2.2 solar masses to collapse into a black hole.
Neutron stars are also tight, compact objects, but their gravity is counterbalanced by internal neutron pressure, which prevents them from collapsing further into black holes.
The item is the first dark stellar remnant — a stellar ‘ghost’ — observed traveling across the galaxy unpaired with another star, whether it is a black hole or a neutron star.
A technique known as gravitational microlensing was used to find the item.
It works by measuring the brightness of a distant star when its light is bent by the gravitational field of a nearby object. They hope to detect many more ghost stars with new observations.
Another team from Baltimore’s Space Telescope Science Institute (STScI) examined the identical microlensing event and discovered that the compact object’s mass is closer to 7.1 solar masses, indicating that it is unmistakably a black hole.
Determining the number of these compact objects in the Milky Way galaxy may aid scientists in better understanding the evolution of stars, particularly how they die, as well as the evolution of our galaxy.
‘As much as we would like to say it is definitively a black hole, we must report all allowed solutions. This includes both lower mass black holes and possibly even a neutron star,’ said Jessica Lu, a UC Berkeley associate professor of astronomy.
Lu’s team also found potential evidence to support a new theory that black holes are not the result of supernovas but instead come from failed supernovas that don’t make a bright splash in the universe.