Astronomers have used the Hubble Space Telescope (HST) to detect the most distant pair of colliding black holes in the known universe. These cosmic behemoths, each estimated to be as massive as 50 million suns, were detected more than 13 billion light-years away, at a time just 740 million years after the Big Bang. While not the biggest or brightest, the merging pair have still managed to grow bafflingly large for such an early time in the universe’s history, the study authors said in a European Space Agency (ESA) press release.
This discovery challenges leading theories of black hole formation, which struggle to explain how objects in the universe’s infancy could grow so large, so fast. ‘Our findings suggest that merging is an important route through which black holes can rapidly grow, even at cosmic dawn,’ the study’s lead author, Johan Übler, a researcher at the University of Cambridge, said in the statement. ‘Together with other Webb findings of active, massive black holes in the distant Universe, our results also show that massive black holes have been shaping the evolution of galaxies from the very beginning.’
Black holes are extraordinarily massive objects with a gravitational pull so strong that nothing, not even light, can escape their clutches. They are thought to form when massive stars collapse in supernova explosions, and they grow by endlessly swallowing up the gas, dust, stars, and other matter in the galaxies that surround them. The hungriest, most active black holes may reach supermassive status — bulking up to be anywhere from a few hundred thousand to billions of solar masses. One key way that supermassive black holes may reach such gargantuan sizes is by merging with other large black holes in nearby galaxies — a process that has been observed at various times and places throughout the universe.
The new discovery comes courtesy of HST’s powerful NIRCam infrared instrument, which can detect the light of ancient objects across vast cosmic distances and through obscuring clouds of dust. In the new study, published Thursday (May 16) in the journal Nature, researchers trained the HST’s infrared cameras on a known black hole system called ZS7, located in an early epoch of the universe known as cosmic dawn. Previous observations showed that the system hosts an active galactic nucleus — a feeding, supermassive black hole at the galaxy’s center, which emits bright light as hot gas and dust swirl around it.
Detailed observations with HST revealed the motion of a dense cloud of gas around the black hole — suggesting it was actively growing — and also pinpointed the approximate location of a second black hole located very close by, likely in the process of merging with the first. ‘Thanks to the unprecedented sharpness of its imaging capabilities, Webb also allowed our team to spatially separate the two black holes,’ Übler said.
The team pegged one of the black holes at about 50 million solar masses; the second black hole, which is ‘buried’ in the dense cloud of gas, likely has a similar mass to its neighbor, but the researchers couldn’t get a clear enough view of its radiation to say for sure.
This exceptionally ancient pair of merging black holes adds further weight to the idea that black holes played a significant role in the infant universe, growing faster than current theories of cosmology can explain. The legacy of these massive mergers can still be felt today in the form of gravitational waves — ripples in the fabric of space-time that were first predicted by Albert Einstein, and that were recently confirmed to be a real phenomenon — that spread across space when massive objects like black holes and neutron stars collide. The ripples released by these faraway, colliding monsters are too faint to be picked up by current gravitational wave detectors on Earth, the study authors added. However, next-generation detectors that will be deployed in space, such as ESA’s planned Laser Interferometer Space Antenna (LISA), scheduled to launch in 2035, should be able to detect even the most distant ripples from merging black holes. The new results suggest that evidence of these ancient mergers may be far more plentiful than previously thought.
