Astronomers have discovered that the nearest black holes near Earth could be hidden within the Hyades Cluster, which sits only around 150 light-years from the Sun. These black holes may have been ejected from the dense cluster of stars millions of years ago to roam the galaxy.
Visible in the Taurus constellation, the Hyades are an open cluster of hundreds of stars. Open clusters like this are collections of stars believed to have formed simultaneously from the same massive cloud of gas and dust. For this reason, it is known that stars within such a cluster share fundamental characteristics such as chemical composition and age.
Simulations using Gaia data
How did we detect what could be the closest black holes near Earth? A team led by Stefano Torniamenti, a researcher at the University of Padua, created a simulation of the movements and evolutions of stars within the Hyades. The simulation also included black holes in the equation. Scientists then compared the results of this simulation with previous observations of the velocities and positions of the stellar population in the cluster. The comparison data set comes from the Gaia space telescope.
“Our simulations can only match the mass and size of the Pleiades if there are some black holes at the center of the cluster” Torniamenti stated in a note (ref.). The team found that models aligning with the observations included two or three black holes. Additionally, simulations involving black holes in the stellar cluster that were theoretically expelled no more than 150 million years ago matched Gaia’s data.
If these black holes were violently expelled from the Hyades when the cluster was about a quarter of its current age, the star cluster would not have evolved enough. Even if the black holes have been expelled from, they would still be the closest black holes to Earth despite their status. This is according to simulations that indicate that if the black holes are not currently in the Hyades, they are in close proximity to the cluster.
Previous record holders
The previous record holders for the closest black hole to Earth were Gaia BH1 and Gaia BH2. As their names suggest, they were discovered using Gaia’s data earlier this year. Gaia BH1 is located 1,560 light-years from Earth, while Gaia BH2 is about 3,800 light-years away. This means that both black holes are still in the cosmic neighborhood of Earth. However, they are over 10 and 20 times farther away than the Hyades cluster and its potential trio of black holes.
Both this new research and the previous discovery of Gaia BH1 and BH2 exemplify how this telescope, launched in 2013, has reshaped astronomy. Gaia has allowed astronomers to study the positions and velocities of individual stars in clusters like the Hyades for the first time. Gaia is capable of such discoveries because it can accurately measure the positions and movements of billions of stars against the backdrop of the sky.
Tracking stellar movements with such precision helps reveal the gravitational influences acting on these stars, even if the influence comes from hidden objects like small black holes. “This observation helps us understand how the presence of black holes influences the evolution of stellar clusters” said Mark Gieles, the study’s author (ref.) and a researcher at the University of Barcelona. “These results also give us an idea of how these mysterious objects are distributed in the galaxy”.