An object mistakenly classified as a star in the Milky Way galaxy is a distant quasar powered by a supermassive black hole that is gobbling up on average the mass of one Sun-sized star per day.

An international team of astronomers said on Monday that the object was the brightest and the fastest-growing quasar discovered so far and had a supermassive black hole about 17 billion times the mass of the Sun. It is so far away that its light has taken 12 billion years to reach Earth.

Quasars, first discovered in 1963, are galaxies with supermassive black holes at their centres that consume gas, dust and anything else within their gravitational pull, their feeding process releasing enormous amounts of energy that make quasars the brightest objects known.

Over the past six decades, astronomers have catalogued about a million quasars.

The new quasar, named J0529-4351, which appeared in a sky survey in June 2022 was initially mislabelled as a star. But observations have now established that it is a quasar with a central supermassive black hole accumulating material at the rate of the mass of 370 Sun-like stars per year — about one Sun per day.

“In terms of luminosity and likely growth rate, J0529-4351 is the most extreme quasar known,” Christian Wolf, an associate professor at the Australian National University, and his collaborators from Chile and France said in a paper published in the journal Nature Astronomy on Monday.

“We’ve discovered the fastest-growing black hole to date,” Wolf said in a media release from the European Southern Observatory, an astronomical facility in Chile.

The matter pulled in towards this black hole, in the form of a disc, emits so much energy that the quasar is over 500 trillion times more luminous than the Sun. “All this light comes from a hot disc measuring about seven light years in diameter,” ANU student Samuel Lai said in a media release from the European Space Agency.

But with 17 billion solar masses, the black hole powering this quasar is not the largest supermassive black hole found yet. It has about one-third the mass of another quasar.

The mechanism underlying the rapid accumulation of the material by the black holes in quasars has been a longstanding question. One possible explanation could be a galactic merger — the collision of two galaxies that will mean much more “food” for the black hole than a single galaxy would provide.

Wolf and his colleagues identified the object as a distant quasar last year using observations from the ANU’s telescope in Australia. They then used the larger telescope and measurements for more precise observations from the ESO’s Very Large Telescope in Chile’s Atacama desert.