For the first time, physicists have observed a black hole accompanied by not one but two celestial objects, raising questions about the origins of black holes.
In a star system 8,000 light-years away from Earth, scientists from the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech) have accidentally discovered a striking phenomenon that has not been previously recorded — a black hole accompanied by two orbiting stars.
In regular star systems, a black hole is accompanied by one star that is consumed by the void. After their formation, black holes are known to be silent killers of galaxies as celestial objects can’t escape their gravitational pull.
The black hole named V404 Cygni at the beginning seemed to be the same, with a small star that spiraled around it every 6.5 days.
However, after a closer look it became obvious that this black hole is unique because another celestial object – a second star – is circulating at a greater distance. Scientists estimate that the second star orbits a black hole every 70,000 years.
The fact that a black hole can hold a star located so far away challenges traditional theories about the birth of a black hole.
Born not from the violent explosion
Previous observations by scientists suggested that black holes are born from violent explosions of dying stars, known as supernovas. When a star runs out of fuel, its core can no longer support its outer layers. Due to its gravity, it collapses to form a black hole.
However, the discovery of this triple tells quite a different story. If V404 Cygni had formed through the explosion, the energy emitted would most definitely have knocked away the distant star from the black hole.
“Imagine you’re pulling a kite, and instead of a strong string, you’re pulling with a spider web,” explains one of the study authors, Kevin Burdge, from MIT Department of Physics.
“If you tugged too hard, the web would break, and you’d lose the kite. Gravity is like this barely bound string that’s really weak, and if you do anything dramatic to the inner binary, you’re going to lose the outer star,” he adds.
That’s why scientists theorize that the black hole formed during a much gentler process than a supernova. They describe the process as a “direct collapse,” where the star collapses without a final explosion. That was later proved by applying model simulations.
“We think most black holes form from violent explosions of stars, but this discovery helps call that into question,” says Burdge.
Accidental discovery
Scientists accidentally made this groundbreaking discovery while searching for new black holes in the Milky Way galaxy.
They used the Aladin Lite online tool, which allows scientists to browse through the repository of astronomical observations gathered from various telescopes in space and around the world.
Led by curiosity, Burdge examined the image of the well-known and documented V404 Cygni black hole, only to be surprised to see two orbiting stars. Despite substantial scientific interest, no previous research has spotted two orbiting stars appearing as two light blobs.
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