Two supermassive black holes in colliding “fossil galaxies” are so massive that they refuse to collide and merge. This discovery may explain why supermassive black hole mergers have been theoretically predicted but never observed.
The supermassive black hole system is located in the elliptical galaxy B2 0402+379. The common mass of two black holes is 28. billion It is many times more massive than 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 together in a pair of supermassive black holes, just 24 light-years apart.
This is the only supermassive black hole binary resolved in sufficient detail to see both objects separately. Interestingly, although the close proximity of the two objects suggests they were bound to collide and merge, they appear to have been locked in the same orbital dance around each other for more than 3 billion years.
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The team, which found the duo in data collected by the Gemini North telescope in Hawaii, thinks that supermassive black holes are prevented from merging due to their enormous mass.
“Normally, galaxies with lighter black hole pairs appear to have enough stars and mass to quickly bring the two together,” Roger Romani, a member of the team and professor of physics at Stanford University, said in a statement. said. “Because this binary was so heavy, it required a lot of stars and gas to get the job done. But the binary cleared the central galaxy of such matter, leaving it stable.”
Supermassive black hole pair not yet compatible
B2 0402+379 is a “fossil cluster” that represents what would happen if the stars and gas from an entire galaxy cluster merged into a single large galaxy. The enormous mass of the two supermassive black holes at its center suggests that a chain of mergers between smaller black holes created them when multiple galaxies in the cluster met and came together.
Scientists believe that at the heart of most, if not all, galaxies is a supermassive black hole with a mass equivalent to millions or billions of suns. No star can collapse to form such massive black holes; Therefore, supermassive black holes are believed to be born through chains of mergers of increasingly larger black holes.
Scientists suggest that when galaxies collide and merge, the supermassive black holes at their hearts move together to form a binary pairing. As they orbit each other, these black holes emit ripples in space-time called gravitational waves, which carry angular momentum from the binary, causing the black holes to orbit closer together.
Eventually, when the black holes are close enough together, their gravitational pull will take over and the black holes will collide and merge, just as black holes collide to form themselves. The question is: Could some supermassive black holes be massive enough to stop colliding?
To better understand this massive black hole system, the team consulted archival data collected by Gemini North’s Gemini Multi-Object Spectrograph (GSO). This allows them to determine the speed of stars near two supermassive black holes and therefore the total mass of these black holes.
“The excellent sensitivity of GMOS allowed us to map the increasing velocities of stars as they looked closer to the center of the galaxy,” Romani added. “With this we were able to deduce the total mass of the black holes present there“
stalled merger
The masses of the two black holes in the system are so large that the team thinks there must be an extraordinarily large population of stars around them to bring the supermassive black holes closer together. But as this happens, energy leaking from the binary system blows matter away from their surroundings.
This left the center of B2 0402+379 devoid of stars and gas close enough to the binary system to leak energy from it. As a result, the progress of these two supermassive black holes towards each other stopped as they approached the final stages before merger.
The team’s results provide important context regarding the formation of supermassive black hole binaries after galactic mergers, but also support the idea that the mass of such binaries is integral in stopping black holes from following suit.
The team is currently unsure whether these two supermassive black holes in this most massive binary ever detected will overcome this pause to eventually merge, or whether they will be permanently locked in merger limbo.
“We look forward to follow-up studies to examine how much gas is present in the core of B2 0402+379,” said Tirth Surti, lead author of the study and a Stanford undergraduate student. “This will give us more insight into whether supermassive black holes may eventually merge or remain trapped as a binary.”
One way to stop this supermassive separation is for another galaxy to merge with B2 0402+379, bringing many more stars, gas, and another supermassive black hole into the mix, disrupting this delicate balance. However, the fact that B2 0402+379 is a fossil galaxy that has not been disturbed for billions of years makes this scenario possible.
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What this research definitively reveals is how useful archival data from telescopes like Gemini North, which is paired with the Gemini South telescope located on a mountain in the Chilean Andes to form the International Gemini Observatory, is to astronomers.
“The data archive serving the International Gemini Observatory holds a gold mine of untapped scientific discoveries,” said Martin Still, National Science Foundation program director for the International Gemini Observatory. “Mass measurements of this extremely supermassive binary black hole are a fascinating example of the potential impact of new research probing this rich archive.”
The team’s research was published in the Astrophysical Journal.