by Two supermassive black holes found in “fossil stars” have been created by collisions so massive that they refuse to collide and merge. The discovery could explain why, although supermassive black hole mergers have been theoretically predicted, they have never been observed taking place.
The supermassive black hole system is located in the elliptical galaxy B2 0402+379. Together, the two black holes have a combined mass of 28 billion times that of the Sun, making it the largest black hole binary ever seen. Not only that, but the binary components of this system are the closest to a pair of supermassive black holes, separated by just 24 light years.
This is the only supermassive black hole binary that has ever been resolved in sufficient detail to see the two objects separately. Curiously, although the proximity of the two bodies suggests they should collide and merge, they appear to have been locked in the same orbit around each other for over 3 billion years.
Related: The pair of supermassive black holes closest to Earth lies on the verge of colliding galaxies
The team that discovered the binary in data collected by the Gemini North telescope in Hawaii think that the supermassive black holes are prevented from merging due to their massive size.
“Typically, galaxies with lighter black hole pairs seem to have enough stars and mass to drive the two together quickly,” said Roger Romani, a member of the team and professor of physics at Stanford University, in a statement . “Since this pair is so heavy, it would have required a lot of stars and gas to do the job. But the binary has scoured the central galaxy for such material, causing it to stall .”
A few super black holes aren’t compatible… yet
B2 0402+379 is a “fossil cluster” that represents what happens when all the star and gas values of a galaxy cluster merge into one massive galaxy. The enormous mass of the two supermassive black holes at its core suggests that they were created by a chain of mergers between the smaller black holes as multiple galaxies in the cluster met and merged together.
Scientists believe that at the center of most, if not all, galaxies is a supermassive black hole with a mass equal to millions or billions of suns. No single star can collapse such supermassive black holes, so supermassive black holes are believed to be formed by successive merger chains of larger and larger black holes.
When the galaxies collide and merge, scientists theorize that the supermassive black holes at their cores move together, creating a binary pair. As they orbit each other, these black holes release a ripple in spacetime called gravitational waves that carry angular momentum out of the binary, causing the black holes to orbit closer together.
Eventually, when the black holes are close enough together, their gravitation should give way, and the black holes collide and merge just as the black holes that collided to create them did . The question is, could some supermassive black hole be so massive that such a collision is stopped?
In order to better understand this system of black hole heavyweights, the team turned to archival data obtained by the Gemini North Multi-Object Spectrograph (GSO). This allows them to determine the speed of the star inside the two supermassive black holes and, in turn, the total mass of those black holes.
“The excellent sensitivity of GMOS allowed us to map the increased velocity of stars as we look closer to the center of the galaxy,” added Romani. “With that, we were able to understand the total mass of the black holes that lived there.”
Merge stopped
The mass of the system’s two black holes is so great that the team thinks it would take a very large population of stars around them to bring the supermassive black holes close together. As this is happening, however, the energy is being leached from the binary by draining matter from its vicinity.
This left the center of B2 0402+379 without stars and gas close enough to the binary to leak energy from it. As a result, these two supermassive black holes have stopped progressing towards each other as they approach the final stages before merging.
The team’s findings provide important context for the formation of supermassive black hole binaries after galactic mergers but also support the idea that the mass of such binaries is central to stopping a black hole from continuing the merger.
The team is currently unsure whether these two supermassive black holes in the heaviest binary ever discovered will eventually overcome this hiatus to merge or whether they will be locked in merger limbo forever.
“We look forward to follow-up investigations of the core of B2 0402+379 where we will look at the amount of gas present,” said lead author of the study and Stanford undergraduate Tirth Surti. “This should give us more insight into whether supermassive black holes can eventually merge or remain stuck as binaries.”
One way to stop this mass extinction would be for another galaxy to merge with B2 0402+379, throwing many more stars, gas, and another supermassive black hole into the mix and upsetting the balance This is sensitive. However, B2 0402+379 is probably a fossil galaxy that has been disturbed for billions of years.
Related Stories:
— a ‘ring’ of black holes colliding across space-time with the vibration of gravitational waves
— Colliding black holes could hide in the light of extremely bright quasars
— 2 merging supermassive black holes visible at ‘cosmic noon’ early in the universe
One thing this research makes clear is how useful archival data from telescopes like Gemini North, which pairs with the Gemini South telescope perched on a mountain in the Chilean Andes to form the International Gemini Observatory, is for astronomers.
“The data archive serving the International Gemini Observatory is a gold mine of untapped scientific discovery,” said Martin Still, the Nations Science Foundation’s program director for the International Gemini Observatory. “Mass measurements for this supermassive binary black hole are an exciting example of the potential impact of new research exploring this rich archive.”
The team’s research is published in the Astrophysical Journal.
