A surprising discovery is expanding the landscape of black holesthe objects they can house and the way in which they are formed. In a study published in Naturephysicists from MIT and Caltech, in the United States, report that They have observed a “triple black hole” for the first time.
The new system contains a central black hole, which consumes a small star which rotates very close to the hole every 6.5 days, a configuration similar to that of most binary systems. But, surprisingly, a second star also appears to be orbiting from the black hole, although at a much greater distance. Physicists estimate that this distant companion orbits the black hole every 70,000 years.
The fact that the black hole appears to have a gravitational pull on such a distant object raises questions about its origin. It is believed that black holes form from violent explosion of a dying star, a process known as a supernova, by which a star releases an enormous amount of energy and light in a final burst before collapsing and becoming an invisible black hole.
However, the team’s discovery suggests that if the observed black hole is the result of a supernova, the energy it would have released before collapsing would have expelled any attached objects in its surroundings. The second star, the outermost one, should not continue circling.
Instead, the team suspects that this black hole was formed through a gentler processin which a star collapses in on itself, forming a black hole without a last dramatic flash. Such an origin would hardly disturb any distant and loosely knit object. The new triple system could be the first evidence of a black hole formed from this softer process.
“We believe that most black holes form from violent explosions of stars, but This discovery helps to cast doubt“says study author Kevin Burdge, a Pappalardo Fellow in the Department of Physics at the M.I.T.. “This system is exciting for black hole evolution, and also raises questions about whether there are more triplets out there.”
The discovery of the triple black hole occurred almost by chance. The physicists found it while consulting Aladin Lite, a repository of astronomical observations, collected from telescopes in space. Astronomers can use the online tool to search for images of the same part of the sky taken by different telescopes.
To analyze the discovery in depth, the researchers turned to Gaia, a satellite which has accurately tracked the movements of all the stars in the galaxy since 2014. The team analyzed the movements of the stars over the last 10 years and discovered that the stars moved exactly in tandem, compared to other neighboring stars.
They calculated that the odds of this type of tandem movement are one in 10 million. “This is almost certainly not a coincidence or an accident,” warns Burdge. “We are seeing two stars that follow one another because they are linked by a weak rope of gravity. Therefore, it has to be a triple system.”
How could the system be formed then?
If the black hole emerged from a typical supernova, the violent burst would have expelled the outer star long ago. “Imagine you’re pulling a kite, and instead of a strong string, you’re pulling a spider web,” Burdge says. “If you pull too hard, the fabric will tear and you will lose the kite. Gravity is like a barely tied rope that is weak and, if you do something drastic with the inner binary, you will lose the outer star.”
However, to really test this idea, Burdge ran simulations to see how such a triple system could have evolved and preserved the outer star. At the beginning of each simulation, you entered three stars. Then performed tens of thousands of simulationseach with a slightly different scenario for how the third star could have become a black hole, and subsequently affected the movements of the other two stars.
It also simulated direct collapse scenarios, in which the third star simply collapsed in on itself to form a black hole, without emitting any energy. “The vast majority of simulations show that “The easiest way to achieve this triple work is through direct collapse.”Burdge declares.
In addition to providing clues about the origin of the black hole, the outer star has also revealed the age of the system. Physicists noted that the outer star is in the process of becoming a red giant, a phase that occurs at the end of a star’s life. Based on this stellar transition, the team determined that the outer star is about 4 billion years old. Since neighboring stars are born at around the same time, the team concludes that the black hole triplet is also 4 billion years old.
“We’ve never been able to do this with an ancient black hole before,” Burdge concludes. “We now know that V404 Cygni is part of a triplet, which could have formed from a direct collapse and that It was formed about 4 billion years agothanks to this discovery.”
