Two closest black holes to Earth discovered

Location of two black holes in the Milky Way. Photo: ESA

Two recently discovered black holes are very close to Earth and may represent a mysterious class of previously unknown giant objects. An international team of astronomers discovered the black holes using data from the European Space Agency's (ESA) Gaia mission and a series of ground-based telescopes around the world . They published the study in the journal Monthly Notices of the Royal Astronomical Society, Live Science reported on April 4.

Named Gaia BH1 and Gaia BH2, the two black holes are closer to Earth than any black holes ever discovered, according to the ESA. Gaia BH1 is 1,560 light-years away from the solar system, toward the constellation Ophiuchus, three times closer than the previous record holder, A0620-00. Gaia BH2 is 3,800 light-years away, toward the constellation Centaurus. Both black holes are about 9 to 10 times more massive than the Sun and are located within the Milky Way.

It has taken astronomers a long time to spot black holes this large because they are virtually invisible. In the past, scientists searched for black holes by looking at the remains of their latest meal. When a star or interstellar gas cloud falls into a black hole, it leaves behind a flash of electromagnetic radiation that astronomers can use to detect the existence of a black hole, according to NASA.

But unlike previous discoveries, Gaia BH1 and 2 are completely dark. They don’t appear to be feeding on anything right now, and they’re completely silent. Instead, the team found the black holes by carefully tracking the movements of two sun-like stars orbiting them. The stars wobble slightly as they move through space, suggesting that something with a strong gravitational pull is pulling them. When the researchers examined the area with telescopes, they couldn’t detect anything emitting radiation. The only explanation was that a black hole was present.

Although both black hole systems were discovered in late 2022, astronomers are beginning to appreciate their uniqueness. The new study suggests that unlike X-ray binaries, pairs of stars and black holes that orbit each other very closely and emit X-rays and radio waves, Gaia BH1 and Gaia BH2 likely represent a group of black holes that have never been seen before. They are located far from their companion stars, said Kareem El-Badry, a researcher at the Harvard-Smithsonian Center for Astrophysics. The team hopes that Gaia's next data transmission in 2025 will help them find more dormant black holes and how they form.

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