From 13 billion light-years away, through the vast expanse of space and time, we’ve recently observed the most distant black hole merger ever detected.
Using the JWST, an international team of astronomers has observed two supermassive black holes and their associated galaxies in the midst of a tremendous cosmic collision, occurring just 740 million years after the Big Bang.
This finding might provide crucial insights into the origins of supermassive black holes and their rapid growth so early in the universe’s history.
“Our research indicates that merging is a significant method by which black holes can quickly increase in size, even during the cosmic dawn,” notes astronomer Hannah Übler from the University of Cambridge in the UK.
“Along with other Webb observations of active, massive black holes in the distant universe, our results demonstrate that massive black holes have influenced galaxy evolution from the very start.”
Black holes are shrouded in mystery, especially regarding the origins of the larger ones. Smaller black holes, up to about 65 times the mass of the Sun, are generally formed through the supernova and core collapse of massive stars; slightly larger ones result from the collisions and mergers of these collapsed stellar cores.
Theoretically, supermassive black holes, millions to billions of times the mass of the Sun, could also grow through a series of hierarchical collisions involving progressively larger black holes, though this is expected to take a considerable amount of time.
A problem arises because we observe very large black holes early in the universe, seemingly too soon for them to have grown through this slow method.
A plausible explanation might be that the initial “seeds” from which these black holes originated were already substantial. Even so, it seems likely that collisions and mergers have also played a role in their subsequent growth to even larger sizes.
One mission of the JWST is to explore how the Universe formed after the Big Bang, utilizing its advanced infrared capabilities to look back at the Cosmic Dawn—the first billion years of the Universe—with unparalleled resolution, specifically searching for supermassive black holes.
In one survey, it detected a pair of galaxies on a collision path, known as system ZS7. At the center of each galaxy is a supermassive black hole, both of which are actively growing, causing the surrounding gas and dust to emit intense light.
“We observed very dense gas moving quickly near the black hole, as well as hot and highly ionized gas lit by the high-energy radiation typically emitted during black holes’ accretion phases,” Übler explains.
“Webb’s exceptional imaging clarity also allowed our team to visually separate the two black holes.”
The team estimated one of the black holes to be about 50 million solar masses. The other was harder to measure due to the dense gas and dust around it but is thought to be of similar mass.
We’ve observed other merging systems later in the Universe; indeed, mergers are considered an integral part of a galaxy’s growth. However, discovering such an early merger supports the theory that both mergers and substantial initial black hole seeds are highly plausible.
These massive mergers are believed to generate a continuous vibration of gravitational waves throughout the Universe.
These wave frequencies are too large to be detected by current gravitational wave detectors (though pulsar observations may have captured them), but by identifying ongoing mergers across different cosmological epochs, scientists can better understand their frequency and contribution to the cosmic hum.
“Our findings provide definite and substantial evidence of a massive black hole involved in a merger with another galaxy, likely containing another accreting black hole, at z = 7.15, just 740 million years after the Big Bang,” the researchers report.
“In conclusion, our data supports the likelihood of a forthcoming massive black hole merger in the early Universe, underscoring this as an additional significant mechanism for the early development of black holes. Along with other recent discoveries, this suggests that massive black hole mergers in the distant Universe are quite common.”
This research has been published in the Monthly Notices of the Royal Astronomical Society.
