Astronomers Discover Galaxy’s Largest Stellar Black Hole ‘Lurking Nearby’

In a record-breaking discovery, scientists have found the largest yet stellar black hole in our galaxy.

The black hole—named Gaia BH3—is thought to be around 33 times as massive as our sun, making it leagues larger than the previous record-holder, Cygnus X-1, which was 21 times the sun’s mass.

Situated around 2,000 light years away from us, this newly discovered black hole is actually the second-closest known black hole to our home solar system, according to a new paper in the journal Astronomy and Astrophysics.

Stellar black holes are a type of black hole that forms from the remnants of enormous stars. When a big enough star runs out of hydrogen fuel to burn, it collapses under its own gravity, exploding in a supernova and leaving behind the star’s huge core. If its core is massive enough, it will collapse into a black hole, an object so dense and with such a great gravitational pull that not even light can escape.

Stellar black holes typically have masses ranging from about 5 to several tens of times the mass of our sun. They are much smaller in mass compared to supermassive black holes, which can be millions to billions of times the mass of the sun and are found at the centers of galaxies, including our own. Therefore, while this newly discovered black hole is the largest stellar black hole in our galaxy, it is still much smaller than the supermassive black hole Sagittarius A* at the center of the Milky Way.

Gaia BH3 was discovered after astronomers analyzed data from the European Space Agency’s Gaia mission, spotting a strange wobbling motion in a star located in the constellation of Aquila. It turns out that this wobbling was being caused by the star orbiting a black hole, namely Gaia BH3. Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and other observatories, astronomers verified the black hole’s mass and determined that it was a staggering 33 times the sun’s mass.

Most other stellar black holes in our galaxy don’t exceed 10 times the mass of our sun, making Gaia BH3 a rare find.

“No one was expecting to find a high-mass black hole lurking nearby, undetected so far,” study author Pasquale Panuzzo, an astronomer at the Observatoire de Paris, part of France’s National Centre for Scientific Research (CNRS), said in a statement. “This is the kind of discovery you make once in your research life.”

The star that orbits Gaia BH3 was hoped to give clues as to the star that died so that the black hole could be born, as binary stars often have similar compositions. Data from the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on ESO’s VLT found that the companion star was very metal-poor, meaning the black hole parent star likely was as well.

Metal-poor stars—predominantly composed of hydrogen and helium, with minimal heavier elements—are believed to retain more mass throughout their lifetimes, potentially leaving behind enough material to form more massive black holes upon their demise. However, direct evidence connecting metal-poor stars to the formation of high-mass black holes has been elusive until now.

There is much more data being gathered on this black hole and its star, but this will not be released in its entirety until 2025.

“We took the exceptional step of publishing this paper based on preliminary data ahead of the forthcoming Gaia release because of the unique nature of the discovery,” paper co-author Elisabetta Caffau, a researcher at CNRS Observatoire de Paris, said in the statement.

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