The brightest object in the known universe is a black hole on a sun-a-day diet

The most luminous object ever observed is so far beyond the reach of its peers that the astronomers who discovered it think it may never be exceeded. Not surprisingly, there are big questions about how something like this could operate so far outside the scale we’re used to.

Black holes are known to have such strong gravitational fields that we cannot see them. However, their accretion disks, in which material such as disassembled stars orbit before being consumed, can be intensely bright. In fact, the accretion disks of supermassive black holes at the centers of galaxies make quasars some of the brightest objects in the universe. The only reason they don’t dominate our skies is because there aren’t any nearby – the nearest quasar is 600 million years ago.

Exactly how luminous quasars can be is an open question, one that has been significantly broadened by the discovery of J0529-4351 using the Siding Spring Observatory and confirmed by observations with the European Southern Observatory’s Very Large Telescope. The apparent brightness of J0529-4351 is comparable to that of two other powerful quasars, J0100+2802 and J2157-3602, and is located at a similar distance of about 12 billion light-years. However, there is one big difference.

J0100+2802 and J2157-3602 are both equipped with a gravity lens; in any case, a closer galaxy concentrates their light so that at our location it appears a lot brighter than it normally would. Taking this lensing into account, these two quasars, while certainly very bright, would be part of the main set of bright quasars we are currently discovering.

The scientists who discovered J0529-4351 were unable to identify any major lens formations. Unless there’s something they missed, this makes it at least an order of magnitude brighter than its apparently comparable counterparts, putting it far ahead of any other quasars, let alone other objects, we know.

“This is also the most luminous object in the universe. It is 200 trillion times brighter than our sun,” Dr. Christian Wolf of the Australian National University said in a statement, adding that he doubts the record will ever be broken. 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 brightness and the rate at which it builds up mass is not perfect. Factors such as the angle at which we see it and how quickly the hole rotates also play a role. Still, the discoverers think they have enough information to calculate the rate at which this monster feeds.

Some bright quasars are powered by a Sun-mass star that is sucked into their accretion disk each year and eventually consumed. J0529-4351 probably does the same thing 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, since we see it earlier after the birth of the universe than some similar objects.

On the one hand, that means that at the time we see it, there wasn’t time to grow to record-breaking size. On the other hand, the feeding speeds could also have been higher. “In the adolescent universe, matter moved chaotically, feeding hungry black holes. Today, stars move orderly at safe distances and only rarely plunge into black holes,” said Professor Rachel Webster of the University of Melbourne.

At this enormous distance we cannot see J0529-4351 in every detail, but closer counterparts give us some powerful hints. “It looks like a giant and magnetic storm cell with temperatures of 10,000 degrees Celsius, lightning everywhere and winds blowing so fast it would go around the Earth in a second,” Wolf said. “This storm cell is seven light-years in diameter, which is 50 percent more than the distance from our Solar System to the next star in the Milky Way, alpha Centauri.”

By combining images from the Digitized Sky Survey 2, we get the overall image, on which there is hardly any visible.  The inset shows the location of the quasar in an image from the Dark Energy Survey

By combining images from the Digitized Sky Survey 2, we get the overall image, on which it is barely visible. The inset shows the location of the quasar in an image from the Dark Energy Survey, still revealing almost no details.

Image credit: ESO/Digitized Sky Survey 2/Dark Energy Survey

The apparent brightness of J0529-4351 is approximately 16e magnitude, comparable to Pluto at the farthest part of its orbit. That means modern professional telescopes can spot it without any problem. The challenge is to notice that it is a quasar rather than a star in our Milky Way. Surveys conducted using the Gaia Space Telescope missed this because their AI search programs were trained on known quasars and failed to recognize something that was so far out of step with other examples. “A human astronomer looking at the Gaia spectrum would recognize the quasar and the redshift at first glance,” the authors noted.

Co-author Dr Christopher Onken said: “It’s a surprise that it has gone unnoticed until now, given what we know about many other, less impressive black holes. It was hidden in plain sight.”

The research has been published in Nature Astronomy.

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