Astronomers think they've discovered a tiny black hole, so low in mass that they had to come up with an exclusive category to put it into.
Besides being small, this black hole is also the closest to us. About 1.500 light-years away from our planet, in the constellation of the Unicorn in the Milky Way, scientists were lucky enough to discover a black hole that is the closest to Earth according to data so far. Due to its unusual properties and the constellation in which it was discovered, the scientists from the University of Ohio who discovered it decided to call it the "Unicorn".
"When we analyzed the data, this black hole, the Unicorn, just popped out," says astronomer Tarindu Jayashingwe. "Why didn't we discover it earlier? It seems we had our astronomical blinds down," adds the scientist.
In theory, black holes can be of different masses - from "tiny" to supermassive giants that drive the hearts of galaxies. However, when it comes to black holes created by the quenching of the cores of dead stars, astronomers have found some "massive gaps" over the years.
If a star with a mass less than 2,3 times that of our Sun dies, general relativity says it will become a neutron star or white dwarf rather than a black hole. Until recently, no black holes smaller than five solar masses had been found.
Before astronomers were able to find smaller black holes, their existence was so unreliable that when they noticed something pulling on a nearby red giant star, they initially dismissed the possibility that it could be a small black hole. But Jayashingwe looked at it from a different perspective. As a PhD student, his mentor told him that small black holes might exist, and he wanted to investigate this.
Analyzing data from various telescope systems and satellites, he focused his attention on a red giant in the constellation of the Unicorn that was in its last stages of life.
The speed of the star, and the way gravity was pulling it, suggested that there was a black hole around it that was pulling it. It is calculated that the size of this dark and silent companion should be approximately three solar masses.
"Just as the Moon's gravity affects Earth's oceans and pulls them towards it and repels them, producing tides, so the black hole warps the star into a shape similar to a rugby ball," explains astronomer Todd Thompson, who was a member of the team that has previously discovered small black holes.
"The simplest explanation is that it's a black hole - and in this case it turned out that the simplest solution was also the most likely," adds Thompson.
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