Astronomers have accidentally discovered the most massive stellar black hole ever detected in the Milky Way galaxy, according to a study published in Astronomy & Astrophysics.
A stellar black hole is caused by the collapse of a star—typically after a supernova explosion—but is much smaller than Sagittarius A*, the supermassive black hole at the Milky Way’s center. It’s four million times the sun’s mass, while “Gaia BH3” is 33 times the sun’s mass.
Unexpected Discovery
Gaia BH3 is 2,000 light-years away in the constellation Aquila and is the second-closest known black hole to Earth. Most are 10 times as massive as the sun. The next most massive black hole in the galaxy, Cygnus X-1, is only 21 solar masses.
“No one was expecting to find a high-mass black hole lurking nearby, undetected so far,” said Pasquale Panuzzo, an astronomer at the Observatoire de Paris, part of France’s National Centre for Scientific Research (CNRS) and a Gaia collaboration member. “This is the kind of discovery you make once in your research life.”
Companion Star
It was discovered in data from the European Space Agency’s Gaia mission while scientists prepared a bulk release of data to the scientific community in 2025.
Gaia detected the black hole because of its effect on the orbit of its companion star. The observations were double-checked using data from the European Southern Observatory’s Very Large Telescope in Chile’s Atacama Desert.
Metal-Poor Star
The discovery of such a massive black hole provides evidence that black holes can form from the collapse of metal-poor stars, which have fewer elements heavier than hydrogen and helium (in astronomy, “metal” is shorthand for elements heavier than hydrogen and helium). The companion star to BH3 was found to be very metal-poor, suggesting that the star that collapsed to form the black hole was also metal-poor.
These stars are thought to lose less mass over their lifetimes, so they may leave more material to produce high-mass black holes after their death.
The study authors chose to publish their findings early to allow other astronomers to begin studying this exceptional black hole immediately and hopefully discover whether it’s pulling in matter from its surroundings.
Wishing you clear skies and wide eyes.
