April 18 2024
The European Space Agency reported finding – by chance – a stellar black hole 33 times the mass of the Sun, lying dormant in the constellation Aquila making it the second closest stellar black hole to the Earth to have been discovered.
On April 16th 2024, astronomers from the European Space Agency released a report in the journal of Astronomy and Astrophysics, proclaiming a serendipitous discovery of a dormant stellar black hole lurking a mere 2000 light years from Earth, with a mass 33 times that of our Sun, making it not only the second closest black hole to the Earth but also the largest stellar black hole in the Milky Way.
The sleeping giant was named Gaia-BH3 for the European Space Agency’s mission Gaia, which discovered it. Gaia is a grand endeavor to map the Milky Way. The mission has indeed been successful, operating 1.5 million kilometers from Earth for the past 10 years and in 2022, it delivered a 3D map of the positions and motions of close to 2 billion stars.
Gaia’s precision mapping was what allowed it to discover the hidden black hole. It picked up a slight “wobble” in the orbit of one of the stars of the constellation Aquila. The star, 75% the mass of the Sun, was revolving around something invisible, prompting further inquiry because the wobbles are tell-tale signs of black holes when they aren’t accounted for by the presence of another star or planet. The European Southern Observatory’s on-ground-telescope in the Atacama Desert, the Very Large Telescope, confirmed that it was indeed a black hole with 33 times the mass of the Sun.
The discovery came as a surprise because no one was hunting black holes, one just gave itself away.
“It’s a complete surprise,” said Dr Pasquale Panuzzo, an astronomer and member of the Gaia collaboration at the Observatoire de Paris. “It is the most massive stellar origin black hole in our galaxy and the second nearest discovered so far.”
Black holes are usually detectable by their gravitational pull on objects around them and the X rays they emit and the jets of light at the outer edges. But since BH3 lay dormant (not pulling surrounding matter in), it had to be discovered in other ways.
As George Seabrook, a scientist at Mullard Space Science Laboratory at University College London and a member of Gaia’s Black Hole Task Force, said “Finding Gaia BH3 is like the moment in the film ‘The Matrix’ where Neo starts to ‘see’ the matrix. In our case, ‘the matrix’ is our galaxy’s population of dormant stellar black holes, which were hidden from us before Gaia detected them.”
Gaia-BH3, like other stellar black holes, was formed when a massive star collapsed inward at the end of its life. Most stellar black holes in the Milky Way are around 10 the mass of the Sun, making BH3 one of the few exceptions. Before BH3 usurped it as the Milky Way’s largest stellar black hole, the title was held by Cygnus X-1, which is 21 times the mass of the Sun. And the black hole closest to Earth (and still holding on to that distinction) is Gaia-BH1, also discovered by Gaia. It is only 1560 light years from the Earth, though it only has a mass 9.6 times that of the Sun.
There are quite a few reasons this discovery has astronomers in a tizzy. Dr. Panuzzo explains that “We have only seen black holes of this mass with gravitational waves in faraway galaxies. This makes the link between the stellar black holes we see in our galaxy and those gravitational wave discoveries. As soon as this comes out, people will rush to see if there are any emissions from the black hole. That will tell us about the wind that comes from stars like the one orbiting the black hole, and also about the physics of the black hole and how matter falls into it.”
Tsevi Mazeh, a scientist and Gaia collaboration member at Tel Aviv University adds that “Gaia -BH3 is the very first black hole for which we could measure the mass so accurately.” This black hole has a mass typical of what astronomers have estimated the very distant black holes observed by gravitational wave experiments to have. “Gaia’s measurements provide the first indisputable proof that [stellar-mass] black holes this heavy do exist.”
It is exciting to think that it was only in 1964 that the first black hole was discovered. Now, we know of black holes in faraway galaxies, millions of lightyears from the Earth. Our technology is becoming sophisticated enough that it is allowing us to look at places we could never dream of reaching. Yet. How much further can we go? And what are we going to discover? Perhaps, the fantasy of encountering aliens will become reality if we could only reach a little further…
