Hundreds of millions of black holes may exist nearby

At the center of our galaxy, there is a supermassive black hole known as Sagittarius A*. The area is also filled with young stars, gas, and dust, leading to a complex environment that is hard to study. Most notably, stellar-mass black holes are present but remain largely unknown due to the difficulty in observing them. Traditionally, scientists have estimated that there might be around 300 stellar-mass black holes near Sagittarius A*. However, a new study published in Astronomy & Astrophysics suggests that there could be many more. Researchers propose a model called the "star grinder," which explains how black holes could accumulate in this region. The model suggests that the dense gas and dust near Sagittarius A* allow for the easy formation of large, short-lived stars. When these stars die, they explode as supernovae, leaving behind black holes. This cycle repeats over time, leading to a buildup of black holes in the area. As their numbers increase, collisions between black holes and stars become more frequent, further accelerating the formation of both. If this theory is accurate, the center of our galaxy might be home to millions or even billions of stellar-mass black holes. Researchers are exploring a concept called collision time to validate this model. Collision time estimates how long it would typically take for a star to collide with a black hole, which varies based on their numbers and sizes. The study found that the largest O-type stars are relatively scarce near Sagittarius A*, indicating they may be frequently destroyed by black holes. In contrast, smaller B-type stars are more plentiful, suggesting they escape such encounters. The authors estimate there are about 100 million black holes per cubic parsec in this area. The model may also help explain the existence of hypervelocity stars in our galaxy. These stars travel at incredible speeds and could gain that speed from close encounters with black holes. Such interactions at the center of the Milky Way could explain why we observe these exceptionally fast stars.