“We have discovered the fastest-growing black hole known to date. It has a mass of 17 billion Suns and eats just over a Sun per day. This makes it the most luminous object in the known Universe” says Christian Wolf, an astronomer at the Australian National University (ANU) and lead author of the study published today in Nature Astronomy.
Quasars are the glowing cores of distant galaxies powered by supermassive black holes. These black holes accumulate matter from their surroundings, emitting vast amounts of light in the process. Consequently, quasars are some of the brightest objects in the sky, visible even from great distances. Generally, the most luminous quasars indicate the fastest-growing supermassive black holes.
However, finding quasars requires precise observational data from large areas of the sky. The massive datasets involved often necessitate the use of machine-learning models to differentiate quasars from other celestial objects. However, these models are trained on existing data, which limits their ability to identify new, more luminous quasars. A new quasar of unprecedented luminosity might be misclassified as a star not far from Earth.
An automated analysis of data from the European Space Agency’s Gaia satellite initially misclassified J0529-4351 as a star due to its brightness. Researchers at ANU eventually identified it as a distant quasar last year using observations from the ANU 2.3-meter telescope at the Siding Spring Observatory in Australia. Identifying it as the most luminous quasar ever observed required more precise measurements, which were obtained using the X-shooter spectrograph on ESO’s VLT in the Chilean Atacama Desert.
It’s 500 trillion times brighter than the Sun
The quasar, named J0529-4351, is located so far from Earth that its light took over 12 billion years to reach us. The matter being pulled in toward this black hole forms a disc that emits so much energy that the quasar is over 500 trillion times more luminous than the Sun.
ANU PhD student and co-author Samuel Lai remarked, “All this light comes from a hot accretion disc that measures seven light-years in diameter — this must be the largest accretion disc in the Universe.” To put that in perspective, seven light-years is about 15,000 times the distance from the Sun to the orbit of Neptune.
Remarkably, this quasar had been hiding in plain sight. Co-author Christopher Onken from ANU said, “It is a surprise that it has remained unknown until today, when we already know about a million less impressive quasars. It has literally been staring us in the face until now.”
The object appeared in images from the ESO Schmidt Southern Sky Survey dating back to 1980, but it was only recognized as a quasar decades later.
Studying distant supermassive black holes can provide important insights into the early universe, including the formation and evolution of these black holes and their host galaxies.