The Milky Way should be full of small black holes. It is believed that in the corners of galaxies there are 10 million to 1 billion black holes with a mass comparable to that of a star.
However, unlike supermassive black holes that are bright and gather galaxies around them, small black holes are very difficult to find. Only 20 stellar-mass black holes are currently known, with the nearest example being about 1,565 light-years away.
New research suggests black holes could be much closer. By analyzing and modeling the Hyades star cluster, a group of stars 150 light-years away, the astronomer discovered that two or three small black holes may be hiding there. The University of Barcelona reports this in a scientific article published in the monthly notices of the Royal Astronomical Society.
“The model can only match the observed mass and size of the Hyades if black holes are present at the center of the cluster,” says astrophysicist Stefano Torniamenti of the University of Padua.
The Hyades, visible in the night sky in the constellation Taurus, are a so-called open star cluster – a group of stars with similar characteristics, moving together in space and bound by gravity.
Each open cluster is essentially a family of stars born from the same molecular cloud that stay together before breaking up. The Hyades are about 625 million years old and contain hundreds of stars, with the stars farthest from the center appearing to separate and those in the center closest together.
Unfortunately, the exact location of the black holes in the cluster has not yet been determined. However, they do not threaten us at all: the maximum possible speed of movement of these black holes was 3 kilometers per second.
It would take a very long time for them to get here, even if they went our way. And in any case, these black holes have no more gravity than any star of equivalent mass.
“This discovery helps us understand how the presence of black holes influences the evolution of star clusters and how star clusters in turn contribute to the formation of gravitational wave sources. galaxy,” says astrophysicist Marc Giles of the University of Barcelona.
