Astronomers believe 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 interesting up close.
About 1,500 light-years from our own planet, in a constellation of the Milky Way known as Monoceros, this is the closest candidate black hole to our planet, scientists have still been lucky enough to find.
The team at Ohio State University called it the Unicorn – a top hat for the black hole house and its extremely rare nature.
“When I analyzed the data, this black hole – the Unicorn – just came out,” says astronomer Tharindu Jayasinghe.
So how come I haven’t seen her before? As it turns out, we had our astronomical blinds on.
From the primordial small ones to supermassive giants that feed the hearts of galaxies, the theory predicts that black holes can exist in a number of masses. However, when it comes to black holes formed by the collapsed cores of dead stars, astronomers have found some “mass gaps” over the years.
If a star collapses to about less than 2.3 times the mass of our Sun, it becomes a neutron star, not a black hole. And, until recently, we didn’t find any black stellar hole smaller than 5 solar masses – which leaves us with the mass gap.
Before we found objects in this gap, their existence had been so dubious that when astronomers noticed a huge red star nearby drawn by something, they initially rejected the possibility that it was a small unseen companion.
But Jayasinghe looked at her differently. As a graduate student, his leader had told him about the potential for extremely small black holes and he wanted to investigate.
Analyzing data from various telescope and satellite systems, he gathered a red giant from the constellation Monoceros, which was in its last stages of life.
The speed of the star and the way it was pulled by gravity suggested that there was a small black hole orbiting around it. The size of this dark and silent companion was calculated to be about 3 solar masses.
“Just as the gravity of the Moon distorts the Earth’s oceans, causing the sea to swell to and from the Moon, producing high tides, so the black hole distorts the star in a football-like shape, with one axis longer than the other.” explains astronomer Todd Thompson, who 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.”
For decades, it was unclear if there was anything in the mass gap between two dead star shapes.
The unicorn now joins several small black holes to help solve this mystery. The results have not yet been officially verified, but for now, this seems to be a strong candidate for another black hole in the middle of the table gap.
“I think the field is heading for this, to really identify how many small masses, how many intermediate masses, and how many large black holes there are,” says Thompson, “because every time you find one, it gives you a clue about which stars are collapsing, which are exploding and which are between them. ”
Who knows how many smaller black holes are there for us to find. Ready or not, here come the astronomers.
The results were accepted for publication in Monthly notifications from the Royal Astronomical Society and prepress can be found here.