The Milky Way should be teeming with small black holes. It is believed that in the corners of galaxies there are from 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 themselves, small ones are very difficult to find. Only 20 stellar-mass black holes are currently known , with the nearest one to Earth being about 1,565 light-years away.
New research suggests black holes may 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. This was reported by the University of Barcelona, 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 from the University of Padua .
The Hyades, visible in the night sky in the constellation Taurus, is a so-called open cluster – a group of stars with the same characteristics, moving together in space, gravitationally bound.
Each open cluster is essentially a family of stars born from the same molecular cloud that stick together before moving apart. The Hyades are about 625 million years old and contain hundreds of stars, with those furthest from the center appearing to begin to separate and those at the center clustering most tightly.
Unfortunately, the exact location of the black holes in the cluster has not yet been determined. However, they definitely do not threaten us: the maximum possible speed of movement of these black holes was 3 kilometers per second.
It would take them a very, very long time to get here, even if they were heading in our direction . And in any case, these black holes have no more gravitational force than any star of equivalent mass.
“This discovery helps us understand how the presence of black holes affects the evolution of star clusters and how star clusters, in turn, contribute to the formation of sources of gravitational waves, as well as providing insight into how these mysterious objects are distributed throughout the galaxy,” says the astrophysicist Marc Giles from the University of Barcelona.
