Astronomers may have discovered the first free-floating black hole in the Milky Way galaxy.
The death of large stars leaves behind black holes but the problem is, isolated black holes are invisible.
Now, astronomers have for the first time discovered what may be a free-floating black hole by observing the brightening of a more distant star as its light was distorted by the object’s strong gravitational field — so-called gravitational microlensing.
The compact object — estimated by UC Berkeley astronomers to be between 1.6 and 4.4 times the mass of our sun — could be a free-floating black hole, one of perhaps 200 million in the Milky Way galaxy.
Because astronomers think that the leftover remnant of a dead star must be heavier than 2.2 solar masses to collapse into a black hole, the researchers caution that the object could be a neutron star instead of a black hole.
Neutron stars are also dense, highly compact objects, but their gravity is balanced by internal neutron pressure, which prevents further collapse to a black hole.
Whether a black hole or a neutron star, the object is the first dark stellar remnant — a stellar ‘ghost’ — discovered wandering through the galaxy unpaired with another star.
The object was discovered thanks to a technique called gravitational microlensing.
It works by observing the brightening of a more distant star as its light is distorted by an object’s strong gravitational field. With new observations, they hope to find many more such ghost stars.
Another team from the Space Telescope Science Institute (STScI) in Baltimore analysed the same microlensing event and found that the mass of the compact object is closer to 7.1 solar masses and indisputably a black hole.
Determining how many of these compact objects populate the Milky Way galaxy will help astronomers understand the evolution of stars — in particular, how they die — and 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.
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