Massive Black Hole Collision in ‘Fossil Galaxies’ Defies Merger, Raises Questions
In a groundbreaking discovery, scientists have found two supermassive black holes locked in a cosmic dance within “fossil galaxies.” These colossal black holes, located in the elliptical galaxy B2 0402+379, are so massive that they refuse to collide and merge, defying theoretical predictions. This discovery raises questions about the nature of supermassive black hole mergers and why they have never been observed in progress.
The joint mass of the two black holes is a staggering 28 billion times larger than that of the sun, making this the most massive black hole binary ever seen. What makes this finding even more remarkable is that the binary components are separated by just 24 light-years, making them the closest supermassive black hole pair ever resolved in such detail.
While the proximity of these two black holes suggests that they should collide and merge, they have been locked in the same orbital dance for over 3 billion years. The team of scientists, who discovered this binary using data collected by the Gemini North telescope in Hawaii, believes that the tremendous mass of the black holes is preventing them from merging.
“Normally, it seems that galaxies with lighter black hole pairs have enough stars and mass to drive the two together quickly,” says Roger Romani, a physics professor at Stanford University. “Since this pair is so heavy, it required lots of stars and gas to get the job done. But the binary has scoured the central galaxy of such matter, leaving it stalled.”
B2 0402+379 is a “fossil cluster,” which represents what happens when an entire galaxy cluster’s worth of stars and gas merge into one massive galaxy. The immense mass of the two supermassive black holes suggests that a chain of mergers between smaller black holes created them as multiple galaxies in the cluster met and merged together.
Scientists believe that supermassive black holes are born through chains of mergers between successively larger black holes. When galaxies collide and merge, the supermassive black holes at their centers move together, forming a binary pairing. As they orbit around each other, these black holes emit gravitational waves that carry angular momentum away from the binary, causing the black holes to orbit more closely together.
Eventually, when the black holes are close enough, their gravitational attraction should take over, and they should collide and merge. However, the question arises: could some supermassive black holes be so massive that such a collision is stalled?
To better understand this system of black hole heavyweights, the team turned to archival data harvested by Gemini North’s Gemini Multi-Object Spectrograph (GSO). This allowed them to determine the speed of the stars near the black holes and, consequently, the total mass of the black holes.
“The excellent sensitivity of GMOS allowed us to map the stars’ increasing velocities as one looks closer to the galaxy’s center,” explains Romani. “With that, we were able to infer the total mass of the black holes residing there.”
The mass of the two black holes in this system is so great that it would take an exceptionally large population of stars around them to bring them close together. However, as this has been happening, the energy leached from the binary has been flinging matter away from their vicinity. This has left the center of B2 0402+379 devoid of stars and gas close enough to the binary to leach energy from it. As a result, the progress of these two supermassive black holes toward each other has stalled.
The team’s findings shed light on the formation of supermassive black hole binaries after galactic mergers and support the idea that the mass of such binaries plays a crucial role in stalling their merger. However, it remains uncertain whether these two supermassive black holes will eventually merge or remain locked in merger limbo permanently.
“We’re looking forward to follow-up investigations of B2 0402+379’s core where we’ll look at how much gas is present,” says Tirth Surti, the lead author of the research. “This should give us more insight into whether the supermassive black holes can eventually merge or if they will stay stranded as a binary.”
One possible scenario that could halt this supermassive stand-off is if another galaxy merges with B2 0402+379, introducing more stars, gas, and another supermassive black hole into the mix. Given that B2 0402+379 is a fossil galaxy undisturbed for billions of years, this scenario is likely.
This research highlights the importance of archival data from telescopes like Gemini North in advancing our understanding of the universe. The data archive serving the International Gemini Observatory holds immense potential for scientific discovery, as demonstrated by the mass measurements of this extreme supermassive binary black hole.
“The data archive serving the International Gemini Observatory holds a gold mine of untapped scientific discovery,”
