The most luminous object ever observed is so far outside the range of its peers that the astronomers who discovered it think it might never be exceeded. Not surprisingly, there are big questions about how something like this could operate so far off the scale we are used to.
Black holes famously have such strong gravitational fields that we can’t see them. However, their , where material such as disassembled stars orbits prior to being consumed, can be intensely bright. Indeed, the accretion disks from supermassive black holes at the centers of galaxies make quasars the brightest objects in the universe. The only reason they don’t dominate our skies is that there are none nearby – the nearest quasar is .
Just how luminous quasars can be is an open question, one that has been pushed considerably wider by the discovery of J0529-4351 using the Siding Spring Observatory and confirmed with observations on the European Southern Observatory’s . J0529-4351’s apparent brightness is similar to two other powerful quasars, J0100+2802 and J2157-3602, and lies at a similar distance of around 12 billion light-years. There is, however, one big difference.
J0100+2802 and J2157-3602 are both ; in each case a closer galaxy focuses their light so that it appears a great deal brighter at our location than it normally would. Allowing for this lensing, these two quasars, while certainly very bright, would be part of the main pack of bright quasars we are in the process of discovering.
The scientists who discovered J0529-4351 could not identify any major lensing. Unless there is something they missed, this makes it at least an order of magnitude more luminous than its apparently similar counterparts, putting it far ahead of any other quasars, let alone other objects, we know.
“This is also the most luminous known object in the universe. It’s 200 trillion times brighter than our sun,” said Dr Christian Wolf of the Australian National University in a , adding he doubts the record will ever be beaten. An alternative estimate puts the figure at 500 trillion, but what is 300 trillion times the brightness of the Sun between friends?
The relationship between a quasar’s luminosity and the rate at which it accretes mass is not perfect. Factors such as the angle we are seeing it at, and how fast the hole is spinning, also play a part. Nevertheless, the discoverers think they have enough information to calculate the rate at which this monster is feeding.
Some bright quasars are powered by a star the mass of the Sun being drawn into their accretion disk, and eventually consumed, every year. J0529-4351 is probably doing the same every day.
J0529-4351 isn’t the most massive black hole ever found, but at 17 billion solar masses it’s certainly up there. The apparent contradiction between its exceptional brightness and its more ordinary mass is explained by its age, as we are seeing it sooner after the birth of the universe than some comparable objects.
On the one hand than that means that at the point at which we see it there hadn’t been time to grow to record-breaking size. On the other hand, feeding rates could also have been be higher then. “In the adolescent universe, matter was moving chaotically and feeding hungry black holes. Today, stars are moving orderly at safe distances and only rarely plunge into black holes,” Professor Rachel Webster from the University of Melbourne said.
At this vast distance we can’t see J0529-4351 in any detail, but closer counterparts give us some powerful hints. “It looks like a gigantic and magnetic storm cell with temperatures of 10,000 degrees Celsius, lightning everywhere and winds blowing so fast they would go around Earth in a second,” Wolf said. “This storm cell is seven light years across, which is 50 per cent more than the distance from our solar system to the next star in the Galaxy, alpha Centauri.”
J0529-4351’s apparent brightness is around 16th magnitude, similar to Pluto at the furthest part of its orbit. That means modern professional telescopes have no trouble spotting it. The challenge is noticing that it is a quasar rather than a star within our galaxy. Surveys conducted using the Gaia space telescope missed it because their AI search programs had been trained on known quasars, and didn’t recognize something so far out of step with other examples. “A human astronomer looking at the Gaia spectrum would recognize the quasar and redshift at first sight,” the authors observed.
Co-author Dr Christopher Onken said, “It’s a surprise it remained undetected until now, given what we know about many other, less impressive black holes. It was hiding in plain sight.”
The study is published in .