Several black holes may have been found in the nearby Hyades cluster. If they are confirmed, they would be the closest black holes to Earth – only 150 light-years away.
A team of astronomers have hinted at the possible existence of neighbouring black holes in a paper published in the journal Monthly Notices of the Royal Astronomical Society.
The Hyades cluster is the nearest “open cluster” to Earth. These clusters are loosely bound groups of stars numbering from a few dozen to a few hundred. In Greek mythology, the Hyades were the five daughters of Atlas and half-sisters to the Pleiades.
Hyades contains several hundred stars, is estimated to be about 650 million years old and is about 20 light-years across. It is one of the most well-studied star clusters.
A team of astrophysicists used computer simulations to track the motion and evolution of all the stars in the cluster. Their aim was to reproduce the current state of the cluster. This was then compared with the actual positions and trajectories of the Hyades stars, which are known to high precision thanks to observational data from the European Space Agency’s Gaia satellite.
“Our simulations can only simultaneously match the mass and size of the Hyades if some black holes are present at the centre of the cluster today (or until recently),” says the paper’s first author Dr Stefano Torniamenti from Italy’s University of Padua.
Simulations most closely match the known location and velocities of stars in the cluster when Hyades is home to 2 or 3 small black holes. Other simulations where all the cluster’s black holes were ejected less than 150 million years ago also give good results.
The results suggest that the black holes should still be inside the cluster, or very close to it. This makes them about 10 times closer than the previous candidate for closest black hole to Earth – the black hole Gaia BH1, which is about 1,500 light-years away.
Even at this distance, the black holes present no immediate threat to us on Earth.
“This observation helps us understand how the presence of black holes affects the evolution of star clusters and how star clusters in turn contribute to gravitational wave sources,” says co-author Mark Gieles from the University of Barcelona in Spain. “These results also give us insight into how these mysterious objects are distributed across the galaxy.”
The hints of the closest black holes to Earth follow the announcement in July that NASA’s James Webb Space Telescope has spotted the furthest black hole yet seen – about 13.2 billion light-years away.