by Astronomers have discovered two new black holes that are the closest known to Earth and also represent something astronomers have never seen before.
The black holes, designated Gaia BH1 and Gaia BH2, were discovered in data collected by the European Space Agency (ESA) Gaia spatialship.
Gaia BH1 is located just 1,560 light-years from Earth in the direction of the constellation Ophiuchus, while Gaia BH2 is 3,800 light-years away in the constellation Centaurus. In cosmic terms, the two black holes are therefore located in the backyard of the Earth.
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It’s not just the proximity of these black holes to Earth however, this makes them extraordinary. They are orbited by stars at distances much greater than those previously seen in other pairs of black hole companion stars.
“What sets this new group of black holes apart from those we already knew is their wide separation from their companion stars,” said Harvard-Smithsonian Center discovery team leader Kareem El-Badry. for Astrophysics in Massachusetts and Max-Planck. Institute of Astronomy in Germany, said in a press release (opens in a new tab).
“Normal” black hole companion star systems are called X-ray binaries and are usually bright in high-energy X-ray and radio emissions. This makes them easier to find than black holes which don’t swallow matter and therefore don’t emit powerful bursts of energy. Gaia BH1 and Gaia BH2 are completely dark and have been detected via the gravitational effect they have on their companion stars.
“These black holes probably have a completely different formation history than the X-ray binaries,” El-Badry explained. “We suspected that there might be black holes in larger systems, but we didn’t know how they would have formed. Their discovery means we need to adapt our theories about the evolution of binary star systems, because we it is not yet clear how these systems form.”
Gaia is great for spotting ‘invisible’ black holes
Gaia is equipped to make such discoveries because it can accurately measure the position and motion of billions of stars against the background of the sky. Tracking this stellar motion so accurately indicates the gravitational influences exerted on these stars by other stars, orbiting planets and black holes, the researchers said.
“The accuracy of the Gaia data was essential for this discovery,” said Timo Prusti, ESA’s Gaia project scientist. “Black holes were found by tracking the tiny wobble of its companion star orbiting around it. No other instrument is capable of such measurements.”
Observations of Gaia were supported by measurements of the motion of each companion star made by other observatories. For example, follow-up surveys of Gaia BH2 with NASA’s Chandra X-ray Observatory and the ground-based South African MeerKAT radio telescope have revealed no detectable light from this black hole.
“Even if we didn’t detect anything, this information is incredibly valuable because it tells us a lot about the environment around a black hole,” said discovery team member Yvette Cendes, Harvard-Smithsonian Center for Astrophysics.
“There are a lot of particles coming from the companion star in the form of stellar wind,” Cendes said. “But because we haven’t seen any radio light, it tells us that the black hole is not a big eater and that few particles pass through its event horizon. We don’t know why, but we want to know!”
The team will now attempt to discover more widely separated black hole binary systems in the next Gaia data dump, which is expected to be released in 2025. This new data will be based on 66 months of spacecraft observations and will contain more detailed information about the movement. of stars.
“It’s very exciting, because it now implies that these black holes in wide orbits are in fact common in space – more common than binaries where the black hole and star are closer. But the problem is detect them,” concluded Cendes. “The good news is that Gaia is still taking data, and its next data release will contain many more of these stars with mysterious black hole companions.”
The discovery of these two black holes is detailed in an article published at the end of last month in the Royal Astronomical Society Monthly Notices (opens in a new tab).
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