Black holes are one of the most mysterious and fascinating phenomena in the universe. Researchers used simulations and data from the Gaia space telescope to suggest the presence of multiple black holes in the Hyades star cluster, which may be the closest to Earth. A paper published in the journal Monthly Notices of the Royal Astronomical Society suggests that the presence of multiple black holes in the Hyades, the closest open star cluster to the solar system, would make them the closest black holes to Earth detected to date.

The Hyades is the closest star cluster to the sun. The Hyades open star cluster is bright enough to have been noticed thousands of years ago, but it is not as bright or compact as the nearby Pleiades star cluster (M45). Pictured here is an especially deep image of the Hyades, displaying vivid star colors and faint coincident nebulae.

This research is the result of the collaboration of a group of scientists led by Stefano Torniamenti of the University of Padua, Italy, with the strong participation of ICREA Professor Mark Gieles of the School of Physics, Institute of Astronomical Sciences, University of Padua. Barcelona (ICCUB) and the Catalan Institute for Space Research (IEEC) and Friedrich Anders (ICCUB-IEEC).

Specifically, this discovery was made during research carried out by expert Stefano Torniamenti at ICCUB, one of the research units of the IEEC.

New research reveals the possible presence of black holes in the Hyades star cluster, positioning them as the closest black holes to Earth.

Is there a black hole in the Hyades?

Since their discovery, black holes have been one of the most mysterious and fascinating phenomena in the universe and have become the subject of study by researchers around the world. This is especially true for small black holes, as they are observed during gravitational wave detections. Since the first gravitational waves were detected in 2015, experts have observed numerous events corresponding to the merger of pairs of low-mass black holes.

In the published study, a team of astrophysicists used simulations to track the motion and evolution of all the stars in the Hyades cluster (about 45 parsecs, or 150 light-years from the Sun) to recreate their current state.

Open clusters are loosely bound clusters of hundreds of stars that share certain properties, such as age and chemical characteristics. The simulation results were compared with the actual positions and velocities of stars in the Hyades cluster, which are now precisely known from observations by the European Space Agency's (ESA) Gaia satellite.

Gaia is an ambitious mission designed to create a three-dimensional map of our Milky Way, revealing its composition, formation and evolution in the process. Image source: ESA-D. Ducros, 2013

"Our simulations could only match both the mass and the size of the Hyades if some black holes existed at the center of the cluster today (or until recently)," said Stefano Torniamenti, a postdoctoral researcher at the University of Padua and first author of the Hyades paper.

The currently observed properties of the Hyades are best reproduced by simulations of two or three black holes, although simulations in which all the black holes were ejected (less than 150 million years ago, roughly the last quarter of the cluster's age) can still give a good match, because the evolution of the cluster cannot erase the traces of its previous black hole population.

The new results show that the black hole born in the Hyades is still located inside the star cluster, or very close to it. This makes them the closest black holes to the sun, much closer than the previous candidate, the black hole Gaia BH1, which is 480 parsecs from the sun.

In recent years, breakthroughs with the Gaia space telescope have made it possible for the first time to study the positions and velocities of stars in open clusters in detail and to accurately identify individual stars.

Mark Gieles, a member of the Department of Quantum Physics and Astrophysics at the University at Buffalo and leader of the project, said: "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 the source of gravitational waves. These results also provide us with insights into how these mysterious objects are distributed in the Milky Way."