With the help of Very Large Telescope (VLT) of the European Southern Observatory (ESO), astronomers have characterized a bright quasar, discovering that it is not only the brightest of its kind, but also the most luminous object ever observed.
Quasars are the bright cores of distant galaxies, powered by supermassive black holes. This record-breaking quasar's black hole is growing in mass the equivalent of a Sun per day, making it the fastest-growing black hole discovered to date.
The black holes that power quasars remove matter from the environment that surrounds them in a process so energetic that it causes the object to emit enormous amounts of light.
This is why quasars are some of the brightest objects in our sky, with even the most distant ones visible from Earth. As a general rule, the most luminous quasars indicate the fastest growing supermassive black holes.
“We have discovered the fastest growing black hole found to date. This object has a mass of 17 billion suns and consumes 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 published today in the journal Nature Astronomy. The quasar, called J0529-4351, is so far from Earth that its light took more than 12 billion years to reach us.
The matter being pulled towards the black hole, in the form of a disk, emits so much energy that it makes J0529-4351 more than 500 billion times brighter than the Sun.
“All this light comes from a hot accretion disk that measures seven light-years across — this must be the largest accretion disk in the Universe,” says paper co-author Samuel Lai, a PhD student at ANU. Seven light years correspond to about 15 times the distance from the Sun to Neptune's orbit.
Surprisingly, this record-breaking quasar was hiding in plain sight. “It is truly surprising that this object has remained unknown until today, when we already know about a million less impressive quasars. It has literally been looking at us until now,” said co-author Christopher Onken, an astronomer at ANU, who added that this object already appeared in images from ESO's Schmidt Survey of the Southern Sky (ESO Schmidt Southern Sky Survey) dated 1980, but was only recognized as a quasar decades later.
Finding quasars requires accurate observational data from large areas of the sky. The databases resulting from these types of observations are so extensive that researchers often use machine learning models to analyze them and distinguish quasars from other celestial objects.
However, these models are trained on existing data, which limits potential quasar candidates to being identified as objects similar to those we already know. If a new quasar is more luminous than any previously observed, the program may reject it and classify it simply as a near-Earth star.
An automatic analysis of data from the European Space Agency's (ESA) Gaia satellite rejected J0529-4351 as a quasar because it was too bright, suggesting instead that it was a star. Researchers identified it as a distant quasar only last year using observations from the ANU 2,3-meter telescope at the Siding Spring Observatory in Australia.
However, to discover that it was the most luminous quasar ever observed, a larger telescope and measurements carried out by a more precise instrument were needed. ESO's VLT X-shooter spectrograph, located in Chile's Atacama Desert, provided the crucial data.
The fastest-growing black hole ever observed will also be a perfect target for the GRAVITY+ upgrade mounted on ESO's VLT Interferometer (VLTI), which is designed to precisely measure the mass of black holes, including those at great distance from Earth.
Additionally, the Extremely Large Telescope (ELT), a 39-meter telescope also under construction in the Chilean Atacama Desert, will make the identification and characterization of these elusive objects even more viable.
The discovery and study of 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. But that's not the only reason Christian Wolf seeks them out.
“Personally, I just like the chase,” says the researcher. “For a few minutes a day I feel like a child playing treasure hunt again and now I use everything I’ve learned since then.”
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