Astronomers think they have discovered a small black hole, with a mass so small that it places it in an exclusive category. Best of all, it’s excitingly close.
About 1,500 light-years from our own planet, in a Milky Way constellation known as Monoceros, it is the closest black-hole candidate to our planet that scientists have yet to find.
The Ohio State University team called it the Unicorn – a highlight for the home of the black hole and its extraordinarily rare nature.
“When we looked at the data, this black hole – the Unicorn – had just emerged,” says astronomer Tharindu Jayasinghe.
So how have we not seen it before? It turns out that our astronomical blinkers were on.
From small primates to supermassive giants that drive the hearts of galaxies, the theory predicts that black holes can exist in different masses. However, when it comes to black holes formed by the collapsing core of dead stars, astronomers have found a ‘mass gap’ over the years.
When a star collapses to about 2.3 times the mass of our sun, it eventually becomes a neutron star, not a black hole. And until recently, we have not found any black holes that are smaller than 5 solar masses – which leaves us with the mass gap.
Before we found any objects in the gap, their existence was so questionable that when astronomers saw a red giant star in the vicinity being struck by something, they initially rejected the possibility that it was a small unseen companion. .
But Jayasinghe looked at it differently. As a graduate student, his supervisor told him about the possibility of extraordinarily small black holes, and he wanted to investigate.
Analyzing data from various telescopic systems and satellites, he honed a red giant in the Monoceros constellation, which was in its final phase of life.
The velocity of the star and the way it was pulled by gravity all suggested that there was a small black hole orbiting it. The size of this dark and quiet companion was calculated at about 3 solar masses.
“Just as the Moon’s gravity distorts the Earth’s oceans, causing the seas to bulge toward and away from the Moon and produce high tides. others, “explains astronomer Todd Thompson, who has helped find other small black holes in the past.
“The simplest explanation is that it’s a black hole – and in this case, the simplest explanation is the most likely.”
It has been unclear for decades whether something exists in the mass gap between two forms of a dead star.
The Unicorn now joins several other small black holes to solve the mystery. The results have yet to be officially verified, but for now it looks like a strong candidate for another black hole in the middle of the mass gap.
“I think the field is moving after this to really map out how many low-mass, how many intermediate-mass and how many high-mass black holes there are,” says Thompson, “because every time you find one, you give it. a clue as to which stars are collapsing, which are exploding and which in between. ”
Who knows how many little black holes there are still that we can find. Ready or not, here come astronomers.
The results were accepted for publication in the Monthly notices from the Royal Astronomical Society and the pre-print can be found here.
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