Monster black hole powers the brightest known object in the universe

A quasar 500 trillion times brighter than the sun has taken the title of the brightest known object in the universe. It appears to be powered by a supermassive black hole that is devouring a sun-sized amount of mass every day.

Quasars are galactic cores where gas and dust falling into a supermassive black hole release energy in the form of electromagnetic radiation. Christian Wolf at the Australian National University in Canberra and his colleagues first spotted the new brightest quasar, called J0529-4351, in 2022 by combing through data from the Gaia space telescope and looking for extremely bright objects outside the Milky Way that were misidentified as stars.

After following up with further observations from the Very Large Telescope (VLT) in Chile, they have now found it it is the most luminous object in the universe that we know of.

Wolf and his colleagues used a device on the VLT called a spectrometer to analyse the light coming from J0529-4351 and calculate how much was produced by the black hole’s swirling disc of gas and matter, called its accretion disc. This revealed that J0529-4351 is the fastest-growing black hole in the universe, gobbling up around 413 solar masses per year, or more than a sun per day.

Using these light spectra, the researchers also calculated that the mass of the black hole was between 5 billion and 50 billion solar masses.

Wolf and his colleagues also found the previous brightest quasar, which was around half the brightness of J0529-4351, in 2018. Wolf thinks the new discovery is likely to remain the record-holder for some time, as the vast majority of the observable sky has now been surveyed in extreme detail, thanks to extensive star catalogues such as that produced by Gaia. “This is the biggest unicorn with the longest horn on its head that we’ve found. I don’t think we’re going to top that record,” says Wolf.

The quasar’s accretion disc appears to be the widest yet known, at 7 light years across. This presents an unusual opportunity to image the black hole directly and accurately measure its mass, says Christine Done at Durham University, UK. “This is big enough and bright enough that we could resolve it with our current instruments,” says Done. “So we could have a much more direct measure of the black hole mass in this monster, and that’s what I did get quite excited about.”

The VLT is currently having its spectroscopic instruments upgraded as part of the Gravity+ project and should then be able to resolve J0529-4351’s features in detail. This will mean that different parts of the quasar’s accretion disc can be differentiated and better understood, says Done, though it could take a few years.