BH3 was discovered when scientists encountered a star in the constellation Vulture “wobbling” under its own gravity.
Astronomers have discovered a massive black hole formed after a star exploded just 2,000 light-years from Earth.
BH3 is the most massive stellar black hole ever discovered in the Milky Way, and it revealed itself to researchers through the strong tug it exerts on a companion star orbiting the object in the Aquila constellation, the Vulture.
This serendipitous discovery is so significant that scientists released details of the object earlier than planned to allow other astronomers to make additional observations as quickly as possible.
“It's a complete surprise,” said Dr. Pascual Panozzo, an astronomer and member of the Gaia collaboration at the Paris Observatory. “It is the most massive black hole of stellar origin in our galaxy and the second closest black hole yet discovered.”
Stellar black holes form when massive stars collapse at the end of their lives. Dozens of them have been found in the Milky Way, most of which weigh about 10 times the mass of the Sun.
The most impressive black hole in the Milky Way, Sagittarius A, has a combined mass of several million suns. It lies at the heart of the galaxy and was formed not from the explosion of a star, but from the collapse of vast clouds of dust and gas.
Researchers identified BH3 in the latest data set collected by the European Space Agency's Gaia mission. The space telescope was launched in 2013 with the goal of compiling a 3D map of a billion stars.
As the researchers reviewed Gaia's observations, they noticed a clear wobble in one of the stars of Aquila, a constellation that can be seen in the summer sky in the Northern Hemisphere. The movement indicates that the star was pulled by a black hole 33 times larger than the Sun.
Further observations obtained using the European Southern Observatory's Very Large Telescope in the Chilean Atacama Desert confirmed the mass of BH3 and the orbit of the star, which orbits the black hole once every 11.6 years. “Only the central black hole in the Milky Way is more massive than this one,” Panozzo said.
Although BH3 is more massive than other stellar black holes in the Milky Way, it is similar to some of those detected by gravitational waves, or ripples in space-time, that are generated when black holes collide in distant galaxies.
“We have only seen black holes of this mass with gravitational waves in distant galaxies,” Panozzo said. “This establishes the connection between the stellar black holes we see in our galaxy and the detections of gravitational waves.” Details are published in Astronomy and Astrophysics.
Stellar black holes 100 meters across may exist in the Milky Way, but despite their enormous mass and the powerful forces they generate, they can be extremely difficult to detect. “Most of them don't have a star orbiting them, so they're almost invisible to us,” Panozzo said.
Measurements of BH3's companion star found no sign of it being contaminated with material expelled by the starburst that formed the black hole. This discovery indicates that the black hole formed long before the companion star was trapped in its strong gravitational field.
The next tranche of Gaia data is expected to be released in late 2025, but the importance of the discovery prompted the international team to publish details of BH3 earlier so astronomers can study it immediately.
“Once this appears, people will rush to monitor it to see if there is any emission from the black hole,” Panozzo said. “This will tell us about the winds coming from stars like those orbiting the black hole, as well as about the physics of the black hole and how matter falls into it.”
Originally published by Watchman On 04/16/2024 – 08:00
Ian Sample Science Editor
