Astronomers have made a groundbreaking discovery in the Milky Way galaxy, identifying the most massive stellar black hole ever observed. This black hole, known as Gaia BH3 or BH3 for short, was found using data from the European Space Agency’s Gaia mission. It was detected due to the unusual ‘wobbling’ motion it imposes on the companion star orbiting it. Further data from the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and other ground-based observatories confirmed its mass, which is an impressive 33 times that of the Sun. This discovery sets BH3 apart from previously identified stellar black holes in the galaxy, which on average are about 10 times as massive as the Sun.
Interestingly, Gaia BH3 is located remarkably close to Earth, only 2000 light-years away in the constellation Aquila. This proximity makes it the second-closest known black hole to our planet. The black hole was discovered unexpectedly while the team was reviewing Gaia observations for an upcoming data release. This unexpected find has been described as a once-in-a-lifetime discovery by astronomers involved in the project. To confirm the discovery, data from ground-based observatories such as ESO’s VLT and the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument were utilized, providing essential information about the companion star and enabling precise measurements of BH3’s mass.
The discovery of Gaia BH3 has provided valuable insight into the formation of high-mass black holes in the Milky Way. While theories suggest that these black holes may be formed from the collapse of metal-poor stars, direct evidence linking metal-poor stars to high-mass black holes has been lacking until now. The metal-poor nature of BH3’s companion star indicates that the star that collapsed to form this exceptional black hole was also metal-poor, as predicted. This finding sheds light on the properties and composition of stars that give rise to high-mass black holes in our galaxy.
The research study, led by astronomer Pasquale Panuzzo, has been published in Astronomy & Astrophysics, with co-author Elisabetta Caffau emphasizing the significance of the discovery. The decision to publish based on preliminary data ahead of the forthcoming Gaia release reflects the unique nature of this finding, enabling other astronomers to study BH3 without delays. Future observations of this system, using tools like the GRAVITY instrument on ESO’s VLT Interferometer, could provide further insights into the history and behavior of this black hole, including its interactions with surrounding matter.
While Gaia BH3 is not the most massive black hole in the Milky Way, that title belongs to Sagittarius A*, the supermassive black hole at the galaxy’s center, it is the most massive stellar black hole known to have formed from the collapse of a star. This distinction underscores the exceptional nature of BH3 within our galaxy. A collaborative effort involving various observatories and spectrographs contributed to this groundbreaking discovery, highlighting the importance of multi-instrument studies in expanding our understanding of the cosmos. Overall, the identification of Gaia BH3 represents a significant step forward in the study of high-mass black holes and their origins within our own galactic neighborhood.
