Astronomers identified the largest stellar black hole yet discovered in the Milky Way, with a mass 33 times that of the Sun, according to a study published on Tuesday.
The black hole, named Gaia BH3, was discovered “by chance” from data collected by the European Space Agency’s Gaia mission, an astronomer from the National Centre for Scientific Research (CNRS) at the Observatoire de Paris, Pasquale Panuzzo, said.
Gaia, which is dedicated to mapping the Milky Way galaxy, located BH3 2,000 light years away from Earth in the Aquila constellation.
As Gaia’s telescope can give a precise position of stars in the sky, astronomers were able to characterise their orbits and measure the mass of the star’s invisible companion – 33 times that of the Sun.
No one was expecting to find a high-mass black hole lurking nearby, undetected so far. This is the kind of discovery you make once in your research life
Further observations from on-the-ground telescopes confirmed that it was a black hole with a mass far greater than the stellar black holes already in the Milky Way.
Stellar black holes in the Milky Way measure on average only 10 times the mass of the sun. The previously largest known – Cygnus X-1 – has about 21 solar masses.
“No one was expecting to find a high-mass black hole lurking nearby, undetected so far. This is the kind of discovery you make once in your research life,” Panuzzo said in a press release.
The black hole is extremely close to Earth at a distance of “only” 2,000 light years. A light year is the distance that light travels in one year – a distance of 9.46 trillion kilometres.
The stellar black hole was discovered when scientists spotted a “wobbling” motion on the companion star that was orbiting it.
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“We could see a star a little smaller than the Sun [around 75 per cent of its mass] and brighter, that revolved around an invisible companion,” Panuzzo said.
Stellar black holes are created from the collapse of massive stars at the end of their lives and are smaller than supermassive black holes, whose creation is still unknown.
Such giants have already been detected in distant galaxies via gravitational waves.
But “never in ours”, said Panuzzo.
BH3 is a “dormant” black hole and is too far away from its companion star to strip it of its matter and therefore emits no X-rays – making it difficult to detect.
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Gaia’s telescope identified the first two inactive black holes (Gaia BH1 and Gaia BH2) in the Milky Way.
Gaia has been operating 1.5 million kilometres from Earth for the past 10 years and in 2022 delivered a 3D map of the positions and motions of more than 1.8 billion stars.
Black holes are objects with such a strong gravitational force that not even light can escape from them. They are formed when large stars with many times the mass of our sun explode as supernovae at the end of their existence and the remaining stellar remnant collapses.
The analyses of the new discovery were published in the journal Astronomy & Astrophysics.
