The black hole was spotted using the gravity lens technique (Getty)
A black hole, which could be four times the size of our sun, has been spotted “floating freely” in our galaxy alone, researchers say.
Researchers at the University of California say there may be up to 200 million such “free-floating” black holes in our Milky Way galaxy.
Black holes are invisible unless they are part of a stellar binary system or surrounded by an accretion disk.
Researchers have used “gravitational microlensing” – in which a black hole distorts and illuminates the light coming “from behind”, as seen from Earth.
Researchers are still unsure whether the object is a black hole or a neutron star, the “heavy” nucleus left over from a supernova explosion.
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The team, led by graduate student Casey Lam and Jessica Lou, an associate professor of astronomy at the University of California, Berkeley, estimates that the mass of the invisible compact object is between 1.6 and 4.4 times that of the sun.
Because astronomers believe the remains of a dead star must be heavier than 2.2 solar masses to collapse into a black hole, UC Berkeley researchers warn 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 it’s a black hole or a neutron star, the object is the first dark stellar remnant – a stellar “ghost” – discovered, wandering the galaxy, unpaired with another star.
Determining how many of these compact objects inhabit the Milky Way galaxy will help astronomers understand the evolution of stars – especially how they die – and our galaxy.
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This could also reveal whether any of the invisible black holes are primary black holes that some cosmologists believe were produced in large quantities during the Big Bang.
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The analysis of Lam, Lou and their international team has been accepted for publication in The Astrophysical Journal Letters.
The team also concluded that the probable population of black holes in the galaxy is 200 million – about what most theorists predict.
The length of the lens event was the main signal that researchers were looking at a black hole, Lam said. In 2020, she showed that the best way to look for microlens for black holes is to look for very long events.
Only 1% of detectable events with microlenses are probably from black holes, she said, so looking at all the events would be like looking for a needle in a haystack.
But, Lam estimated, about 40% of microlens events that last more than 120 days are probably black holes.
“How long the lightening lasts is a hint at how massive the lens in the foreground is, which bends the light of the background star,” Lam said.
“Long events are more likely due to black holes. However, this is not a guarantee, as the duration of the lighting episode depends not only on how massive the foreground lens is, but also on how fast the foreground lens and the background star move. each other.
“However, by obtaining measurements of the visible position of the background star, we can confirm whether the lens in the foreground is really a black hole.
I’m watching; Footage shows a black hole in the Milky Way
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