A wobble reveals the most massive stellar black hole in our galaxy

By | April 17, 2024

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Astronomers have discovered the most massive known stellar black hole in the Milky Way galaxy after detecting an unusual wobble in space.

The so-called ‘sleeping giant’, called Gaia BH3, has a mass almost 33 times that of our Sun, and is located 1,926 light-years away in the constellation Aquila, making it the second-closest known black hole near the earth. . The nearest black hole is Gaia BH1, which is about 1,500 light-years away and has a mass almost ten times that of our Sun.

Astronomers discovered the black hole while sifting through observations from the European Space Agency’s Gaia Space Telescope for an upcoming data release to the scientific community. The researchers didn’t expect to find anything, but a peculiar motion – caused by Gaia BH3’s gravitational influence on a nearby companion – caught their attention.

Many ‘dormant’ black holes have no companion close enough to feed on, making them much harder to spot and not generating light. But other stellar black holes suck material from companion stars, and this exchange of matter releases bright X-rays that can be seen by telescopes.

The wobbling motion of an ancient giant star in the constellation Aquila revealed that it was in an orbital dance with a dormant black hole, and it is the third dormant black hole that Gaia has spotted.

The researchers used the European Southern Observatory’s Very Large Telescope in Chile’s Atacama Desert and other ground-based observatories to confirm Gaia BH3’s mass, and their research has also provided new clues to how such massive black holes. The findings appeared on Tuesday in the journal Astronomy & Astrophysics.

“No one expected that there would be a high-mass black hole lurking nearby, which had gone unnoticed until now,” said lead author Pasquale Panuzzo, an astronomer at the Observatoire de Paris, part of the French National Center for Scientific Research, and member of the Gaia collaboration. , in a statement. “This is the kind of discovery you make once in your research life.”

The secrets of old stars

The title for the most massive black hole in our Milky Way will always belong to Sagittarius A*, the supermassive black hole at the center of the Milky Way, which has about 4 million times the mass of the Sun, but that’s because it’s a supermassive black hole, instead of a stellar black hole.

The process by which supermassive black holes form is poorly understood, but one theory suggests it happens when massive cosmic clouds collapse. Stellar black holes are formed when massive stars die. Gaia BH3 is thus the most massive black hole in our Galaxy created by the death of a massive star.

Stellar black holes observed in the Milky Way galaxy are on average about ten times as massive as the Sun. Until the discovery of Gaia BH3, Cygnus X-1 was the largest known stellar black hole in our Milky Way, having 21 times the mass of the Sun. Although Gaia BH3 is an exceptional find in our Milky Way by astronomers’ standards, it is comparable in mass to objects found in very distant galaxies.

Three stellar black holes in our Milky Way, Gaia BH1, Cygnus X-1 and Gaia BH3, have masses 10, 21 and 33 times that of the Sun, respectively.  - M. Kornmesser/ESOThree stellar black holes in our Milky Way, Gaia BH1, Cygnus X-1 and Gaia BH3, have masses 10, 21 and 33 times that of the Sun, respectively.  - M. Kornmesser/ESO

Three stellar black holes in our Milky Way, Gaia BH1, Cygnus X-1 and Gaia BH3, have masses 10, 21 and 33 times that of the Sun, respectively. – M. Kornmesser/ESO

Scientists believe that stellar black holes with masses like Gaia BH3 formed when metal-poor stars collapsed. It is believed that these stars, which contain hydrogen and helium as their heaviest elements, lose less mass during their lifetime, ultimately having more material, which can result in a high-mass black hole.

But astronomers hadn’t managed to find evidence directly linking high-mass black holes and metal-poor stars until they discovered Gaia BH3.

The study authors said that paired stars are usually similar in composition. True to expectations, the researchers found that the star surrounding Gaia BH3 was metal-poor, meaning the star that formed Gaia BH3 was likely the same.

“What strikes me is that the chemical composition of the companion is similar to what we find in old metal-poor stars in the Milky Way,” said co-author Elisabetta Caffau, a Gaia collaboration member at the Observatoire de Paris, in a statement.

The star orbiting Gaia BH3 likely formed in the first two billion years after the Big Bang created the universe 13.8 billion years ago. The trajectory of the star, which moves in the opposite direction of many stars in the Milky Way’s galactic disk, suggests it was part of a small galaxy that merged with the Milky Way more than 8 billion years ago.

Now the team hopes the research can allow other astronomers to study the colossal black hole and discover more of its secrets without having to wait for the rest of the Gaia data release, scheduled for late 2025.

“It is impressive to see the transformative impact Gaia is having on astronomy and astrophysics,” Carole Mundell, scientific director of the European Space Agency, said in a statement. “The discoveries extend far beyond the original goal of the mission, which was to create an extremely accurate multi-dimensional map of more than a billion stars in our Milky Way.”

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