Exceptional Black Hole Discovered in the Milky Way

Heidelberg researchers played a leading role in evaluating the data from the Gaia space observatory

Position of Gaia BH3
Position of Gaia BH3

A mere 2,000 light years from Earth lies a black hole approximately 33 times the mass of the sun. The object known as Gaia BH3 - the most massive black hole ever discovered in the Milky Way - was detected with the aid of the Gaia space observatory of the European Space Agency (ESA). Researchers from the Centre for Astronomy of Heidelberg University (ZAH) were crucially involved in analysing the data. Until now, black holes of this type were observed only in very distant galaxies. With the discovery of this "sleeping giant" in the Eagle constellation, scientists hope to learn more about how such massive stars form and evolve.

"Like countless results before it, this discovery is another spectacular reward of twenty years of hard work in Gaia data analysis," states Dr Michael Biermann, who directs astrometric data evaluation at the Institute for Astronomical Computing at Ruperto Carola. Nearly 90 researchers are involved in this work at the ZAH, making it the largest department of the Gaia data processing consortium. It is responsible for the entire processing chain from the satellite’s raw data to the positions, movements, and distances of the stars derived therefrom.

The current discovery was based on ultra-precise measurements over a period of five years, during which the participating researchers became aware of a star with a slightly fluctuating position. This oscillation is caused by an invisible object that the star orbits every twelve years. As Dr Biermann explains, this object is a "sleeping" black hole. Without a neighbouring star from which it can siphon matter, it does not generate any light, making it very difficult to detect. The unusually large black hole formed billions of years ago from a single supernova explosion and not from the merger of less massive black holes, according to the researcher.

"The scientific consequences of the discovery will only become apparent in the course of the coming years. Many telescopes and measuring instruments will now focus on this object in order to study the properties and behaviour of such a massive black hole at close range for the first time," explains Dr Ulrich Bastian, who was directly involved in the paper on Gaia BH3 published in "Astronomy & Astrophysics". According to the ZAH researcher, this discovery offered up proof that even "sleeping" and hence invisible black holes can be detected as long as they pair with a star.

P. Panuzzo et al.: Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry, Gaia Collaboration, Astronomy & Astrophysics, 2024.