When large stars collapse, they are thought to leave behind black holes. If that is the case, there should be hundreds of millions scattered throughout the Milky Way, left behind after the death of those stars.
But scientists have struggled to find them. Isolated black holes are invisible.
Now, researchers believe they have spotted such a “free-floating” black hole, flying through the galaxy at 100,000 miles per hour. It was spotted using gravitational microlensing, where scientists watch for the distortion of light caused by an object’s gravity.
The object is in our galaxy, but still thousands of light years away from us. However, the finding suggests that, statistically, the nearest such object to us should be less than 80 light years away.
It is somewhere between 1.6 and 4.4 times the mass of our Sun, according to one set of scientists. Another, using the same data, believe it to be nearer 7.1 solar masses.
The smaller size estimates means the object could still prove to be a neutron star rather than a black hole. But with the latter, larger calculations, it would certainly be a black hole.
Whatever it is, the object is the first such “ghost” – the dark, dense leftovers of a dead star – that has ever been seen wandering through our galaxy unpaired with another star.
“This is the first free-floating black hole or neutron star discovered with gravitational microlensing,” said Jesica Lu, from UC Berkeley, one of the leaders on one of the studies.
“With microlensing, we’re able to probe these lonely, compact objects and weigh them. I think we have opened a new window onto these dark objects, which can’t be seen any other way.”
The separate research by two competing teams mean that the research is described in two papers: one, by the UC Berkeley team that believes it to be smaller, is published in Astrophysical Journal Letters, while the other larger estimate from the Space Telescope Science Institute is described in The Astrophysical Journal.
As well as estimating different masses, the teams disagree on how far away the object probably is. The UC Berkeley team believes it to be between 2,280 and 6,260 light years away, while the STSci team thinks it is about 5,153 light years from us.
It also means that the object has been given two distinct names: MOA-2011-BLG-191 and OGLE-2011-BLG-0462, or OB110462, for short.
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