Most Luminous Quasar Hosts What Might Be Fastest-Growing Black Hole

Quasars are among the most distant known celestial phenomena. They’re powerful enough to show up in our skies as star-like specks, but in fact each quasar is the luminous region surrounding a supermassive black hole at the center of a galaxy. As the ravenous black hole gobbles up gas from the surrounding disk, the superheated gas falling into it glows brightly, often outshining the rest of the galaxy.

Around a million quasars have been found so far, and with the advent of all-sky surveys, rarer and more luminous quasars are increasingly being detected. But the latest find is the most superlative yet, with an unprecedented luminosity and growth rate.

Now, Christian Wolf (Australian National University) and an international team of astronomers have used publicly available data from the European Space Agency’s Gaia mission and spectra taken by the European Southern Observatory’s Very Large Telescope in Chile to construct a picture of the quasar J0529-4351. Their findings are published in Nature Astronomy.

The team established that J0529-4351 dates back to 1.5 billion years after the Big Bang. The light we see from it has been travelling for most of the universe’s lifetime. While not the most distant quasar known, it is the most luminous known.

Some quasars only appear to be bright because of gravitational lensing, in which foreground mass magnifies the light coming from background objects. The researchers checked this possibility and concluded that no lensing effect is evident — there is a more than 99% chance that J0529-4351 really is that bright.

The researchers also estimated the mass of the supermassive black hole that powers this quasar, finding its mass to be equivalent to 17 billion Suns. That makes it one of the most massive quasars, too.

Based on its luminosity, the black hole is pulling in mass at a rate of some 413 solar masses per year. That’s near the maximum possible for a black hole of this mass — if it pulls in any more, the strong radiation from the spiraling, infalling gas will actually start to push the gas away.

Astronomers have long been intrigued by how supermassive black holes can grow to such large scales so quickly and so early on in the history of the universe. “Finding these extreme objects, such as J0529-4351, is therefore very valuable to test different black hole growth models,” explains Anna-Christina Eilers (MIT), who wasn’t involved in the study. She hails the “really exciting new discovery,” while noting that it raises a number of questions. Leading among them is, how many similar superluminous quasars lie undetected? And where does the fuel that feeds their gargantuan black holes come from?

Shelley Wright (University of California, San Diego), who also wasn’t involved, remarks that, by providing “a glimpse of a distant quasar engaged in a frenzied feeding,” Wolf’s study offers “insights into black hole growth mechanisms.” She pays tribute to the steps taken in the study and “the new method that these authors have articulated for identifying other quasars undergoing similar extreme growth.”

Wright points out that “one of the most exciting aspects of this discovery” is that it increases the sample size of ancient, superluminous quasars. The more such cases that astronomers can draw upon, the easier it is to identify common characteristics.

More observations of extreme quasars are underway with the Atacama Large Millimeter/submillimeter Array, a radio telescope in the Atacama Desert in Chile. A few hundred miles away, in the same desert, the Extremely Large Telescope will soon join in the search. These instruments, in tandem with decades-long repeat observations, will, with luck, unveil further extreme quasars and enable us to see how they change over time.