Fastest-growing black hole 1.2 billion light-years away has massive appetite, eats equivalent of one Sun daily

The fastest-growing black hole in the universe is 34 billion times the mass of our Sun, and it has an appetite to match its size. Known as J2157, the giant black hole eats nearly the equivalent of one Sun every day, according to researchers led by The Australian National University (ANU). The team, which includes experts from the University of Arizona, used the European Southern Observatory or ESO’s Very Large Telescope in Chile to accurately measure the black hole’s mass. The supermassive black hole is 1.2 billion light-years away from Earth and 8000 times bigger than the black hole Sagittarius A*, which is at the center of the Milky Way. J2157 is also the most luminous black hole on record. 

“The black hole's mass is about 8,000 times bigger than the black hole in the center of the Milky Way. If the Milky Way's black hole wanted to grow that fat, it would have to swallow two-thirds of all the stars in our galaxy,” says lead author Dr Christopher Onken, Australian National University, in the analysis published in Monthly Notices of the Royal Astronomical Society. In 2018, astronomers at ANU discovered the ‘monster’ J2157. They looked back more than 12 billion years to the early dark ages of the universe when this supermassive black hole was estimated to be the size of about 20 billion suns with a one percent growth rate every one million years. “We're seeing it at a time when the universe was only 1.2 billion years old, less than 10% of its current age. It's the biggest black hole that's been weighed in this early period of the universe,” emphasizes Dr Onken.

Back in 2018, scientists had quipped that this black hole is growing so rapidly that it is shining thousands of times more brightly than an entire galaxy, due to all of the gases it sucks in daily, causing lots of friction and heat. Experts then said that the energy emitted from this supermassive black hole, also known as a quasar, was mostly ultraviolet light but also radiated X-rays. “If we had this monster sitting at the center of our Milky Way galaxy, it would appear 10 times brighter than a full moon. It would appear as an incredibly bright pin-point star that would almost wash out all of the stars in the sky. Again, if this monster was at the center of the Milky Way, it would likely make life on Earth impossible with the huge amounts of X-rays emanating from it,” says Dr Chris Wolf from ANU, who had led the team in 2018. The SkyMapper telescope at the ANU Siding Spring Observatory detected this light in the near-infrared, as the light waves had red-shifted over the billions of light-years to Earth.

The European Space Agency's Gaia satellite, which measures tiny motions of celestial objects, helped find this supermassive black hole. The Gaia satellite confirmed the object that they had found was sitting still, meaning that it was far away and it was a candidate to be a very large quasar. The discovery was confirmed using the spectrograph on the ANU 2.3 meter telescope to split colors into spectral lines.
According to astronomers, these kinds of black holes can be used as ‘beacons’ to see and study the formation of elements in the early galaxies of the universe. “With such an enormous black hole, we're also excited to see what we can learn about the galaxy in which it's growing. Is this galaxy one of the behemoths of the early Universe, or did the black hole just swallow up an extraordinary amount of its surroundings? We'll have to keep digging to figure that out,” writes Dr Onken.

Exactly how black holes grew so big so early in the life-span of the universe is still a mystery, but the team is now searching for more black holes in the hope they might provide some clues. “We knew we were onto a very massive black hole when we realized its fast growth rate. How much black holes can swallow depends on how much mass they already have. So, for this one to be devouring matter at such a high rate, we thought it could become a new record holder. And now we know,” says team member Dr Fuyan Bian, a staff astronomer at ESO.