All galaxies have a supermassive black hole at the center, a region that absorbs all surrounding matter and, in doing so, releases enormous amounts of energy in the form of visible light and radio frequencies that give rise to quasars, the brightest and hottest objects. of the universe. An international team has just discovered the brightest and most luminous ever observed and the details of the discovery were published this Monday in an article in the journal Nature Astronomy.

Quasars obtain their energy from supermassive black holes and this one is so voracious that it increases its mass by the equivalent of one Sun per day, making it the fastest growing one discovered to date. Furthermore, by collecting matter from their environment, they emit large amounts of light that are visible even from Earth.

For this reason, it currently has “a mass of 17 billion suns and eats just over one sun per day,” making it “the most luminous object in the known universe,” says Christian Wolf, astronomer at the Australian National University (ANU). and lead author of the study.

Astronomers have made this discovery using the European Southern Observatory's (ESO) Very Large Telescope (VLT). According to their calculations, J0529-4351, as this discovery has been named, is so far from Earth that its light took more than 12 billion years to arrive. The matter attracted to this disk-shaped black hole emits so much energy that it is more than 500 billion times more luminous than the Sun.

“All this light comes from a hot accretion disk measuring seven light-years across,” about 15,000 times the distance from the Sun to Neptune's orbit.. “It must be the largest accretion disk in the universe,” concludes Samuel Lai, ANU PhD student and co-author of the study.

Hidden in plain sight

But for the authors, the most surprising thing is that this record-breaking quasar was hiding in plain sight. “It is a surprise that it has not been detected until now, when we already know about a million of these less impressive objects. “It's literally been staring us in the face,” says Christopher Onken, an astronomer at ANU and co-author of the study.

Although this object appeared in images from ESO's Schmidt Southern Sky Survey dating back to 1980, it was not recognized as a quasar until decades later, Onken acknowledges. Searching for them requires precise observational data from large areas of the sky, but such an amount of information can only be analyzed with machine learning models that do the search and differentiate them from other celestial objects.

Because these models are trained with existing data, they can make mistakes and classify discoveries as objects similar to those already known. Thus, if a new quasar is more luminous than any previously observed, the program could reject it and classify it as a star not too distant from Earth.

An automated analysis of data from the European Space Agency's Gaia satellite passed J0529-4351 as too bright to be a quasar, suggesting it was a star. Researchers identified it as a distant celestial object last year using observations from the 2.3-meter ANU telescope, located at the Siding Spring Observatory in Australia.

But discovering that it was the most luminous quasar ever observed required a larger telescope and more precise measurements.. The X-shooter spectrograph installed on ESO's VLT in the Chilean Atacama Desert provided the data that would prove crucial. Detecting and studying distant supermassive black holes could shed light on some of the mysteries of the early universe, including how they and their host galaxies formed and evolved.