Physicists from MIT and Caltech have discovered a first: a triple black hole system, consisting of three bodies orbiting each other about 7,800 light-years from Earth.
Black hole binaries—two-body systems in which at least one is a black hole—are common in the universe. In general, a black hole appears to lift an orbiting star as the latter gets closer to the black hole’s gravitational pull. But the latest discovery pushes the envelope, adding a new body to the equation, revealing a system with one black hole and two stars—a configuration never seen before. A team study describing the program and its newly discovered member was published today on The environment.
“We think that most black holes form due to violent stellar explosions, but this discovery helps question that,” said study author Kevin Burdge, a physicist at MIT and co-author of the study, in the center’s release. “This program is very exciting about black hole evolution, and it also raises questions about whether there are triples out there.”
The system in question is V404 Cygni, which contains a black hole of the same name about nine times the mass of the Sun. First confirmed as a black hole in 1992, V404 Cygni has been extensively studied; In 2022, NASA turned the echoes from the black hole into sounds, allowing us to “hear” the black hole in action. Such echoes of black holes are a good way for scientists to reveal the dense regions around black holes.
Black holes are regions of space that have such strong gravity that light cannot escape, making them completely black. They are generally thought to form in supernovae, the glowing deaths of stars, their remnants collapsing into black holes.
Until now, V404 Cygni was thought to belong to a binary system, consisting of a black hole and a nearby star orbiting it, gradually losing its material to the black hole’s gravity. But according to the team’s new findings, there’s another star in the picture—far away from the black hole, but part of the same system nonetheless.
On average for the group, the inner star orbits the black hole in a little less than a week. In contrast, an outer star orbits the body every 70,000 years. That’s many weeks—3.64 million, to be exact. The outer star is about 3,500 astronomical units (AU) from the black hole, which is the average distance between Earth and the Sun. According to an MIT release, that distance is also 100 times the distance between Pluto and the Sun. In other words, V404 Cygni is something a triple system, but different.
But there is more to this than just the appearance of three bodies on the track. The latter team concluded that a typical supernova does not explain V404 Cygni—such an explosion would have pushed everything around it outwards, essentially ejecting an exoplanet from the triple system. But if not with a supernova, how was a black hole born?
“Most simulations show that the easiest way to do this triple function is through vertical collapse,” Burdge said in the release. A vertical collapse is when a star collapses without the sound of a bright starburst—no energy is released into space as the star collapses into a gravitational behemoth.
Based on the age of that most distant star, the team was able to estimate the age of the entire system threefold: about four billion years. For reference, that’s younger than our spit of rock in the universe (4.6 billion years old), and (perhaps obviously) younger than the universe itself, which clocks in at about 13.77 billion years old.
Of course, this real-life trio is different from the three-body problem described in Cilin Xiu’s best-selling novel of the same name. In the book (spoilers ahead), the three bodies in play were three stars in an impossible position to predict each other. This unexpected movement makes life almost impossible for the aliens of the planet caught between the three stars, forcing them to consider their options outside of their home world. (Spoilers now follow.) The real life system of the three bodies described by the group is much quieter than the one in the book, but also more extreme—one of the bodies is a black hole.
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