“Shy” Black Holes Detected by Gaia Telescope.. A Mystery in Their Orbits

Most of the black holes known to scientists accrete matter from a companion star, emitting radiation that reveals their presence.

But there is a “shy” type that consumes nothing, remaining completely hidden until it is detected by the European Gaia probe through its indirect gravitational signature.

According to Universe Today, the Gaia telescope tracks the motion of more than a billion stars in our galaxy with exceptional precision. Thanks to this, three “sleeping” stellar-mass black holes have so far been discovered, each with a low-mass companion star. This trio is known as Gaia BH1, BH2, and BH3, with the last being the most massive, weighing approximately 33 times the mass of the Sun and located in the constellation Aquila, about 2,000 light-years from Earth.

Notably, for two of the three—BH1 and BH2— their companion stars orbit the black hole at distances much closer than predicted by the standard model of binary star evolution. Only BH3 orbits in a wide enough path to avoid a phase known as “Roche lobe overflow,” during which part of the companion star’s material spills onto the black hole.

To explain this puzzle, a new study published in The Astrophysical Journal proposes a mechanism called “non-conservative mass transfer” as a plausible explanation for the formation of these unusual binary systems, pending further Gaia data to uncover more of these “shy” black holes.