Astronomers have discovered a massive black hole formed in the aftermath of an exploding star just 2,000 light-years from Earth.
BH3 is the most massive stellar black hole ever discovered in the Milky Way, and it revealed its existence to researchers through the powerful gravitational pull it exerts on a companion star orbiting an object in the constellation Aquila.
This serendipitous discovery is so important that the scientists published details of the object earlier than planned so that other astronomers could make further observations as soon as possible.
“It's a complete surprise,” said astronomer Pasquale Panuzzo, a member of the Gaia collaboration at the Paris Observatory. “This is the most massive black hole of stellar origin in our galaxy, and the second closest ever discovered.”
Stellar black holes form when massive stars collapse at the end of their lives. Dozens of them have been discovered in the Milky Way, and most weigh about 10 times the mass of the Sun.
The Milky Way's most impressive black hole, Sagittarius A, has a combined mass of several million suns. It lurks at the center of galaxies and was formed not by exploding stars but by the collapse of vast clouds of dust and gas.
Researchers discovered BH3 in the latest trove of data collected by the European Space Agency's Gaia mission. The space telescope was launched in 2013 with the goal of creating 3D maps of 1 billion stars.
As researchers considered observing Gaia, they noticed that one of the stars in the constellation Aquila, a constellation visible in the northern hemisphere's summer sky, was shaking noticeably. This movement suggested that the star was being pulled around by a black hole with a mass 33 times that of the Sun.
Further observations by the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert confirmed BH3's mass and the star's orbit, which orbits the black hole once every 11.6 years. “Only the black hole at the center of the Milky Way is larger than this black hole,” Panuzzo said.
Although BH3 is more massive than other stellar black holes in the Milky Way, it resembles some of the black holes revealed by gravitational waves, or ripples in spacetime, that occur when black holes collide in distant galaxies .
“We have only observed black holes of this mass in gravitational waves in distant galaxies,” Panuzzo said. “This creates a link between stellar black holes seen in our galaxy and the discovery of gravitational waves.” Details can be found in Astronomy and Astrophysics.
A 100-meter stellar black hole may exist in the Milky Way, but despite its enormous mass and the powerful force it generates, it is extremely difficult to detect. “Most of them don't have stars orbiting around them, so we can barely see them,” Panuzzo says.
Measurements of BH3's companion star showed no evidence that it had been contaminated by material ejected from the explosion of the star that formed the black hole. This discovery suggests that the black hole formed long before it trapped its companion star in its powerful gravitational field.
The next part of the Gaia data is expected to be released as early as the end of 2025, but given the importance of this discovery, the international team is determined to release details of BH3 early so that astronomers can study it immediately. I made it.
“As soon as this becomes clear, people will rush to observe it to see if there is radiation from the black hole,” Panuzzo said. “It will also tell us about the winds blowing from stars like those orbiting black holes, and about the physics of black holes and how matter falls into them.”