AI Error Turns Out to be a Voracious Quasar

Thanks also to the help of the ESO’s VLT, a group of astronomers have studied a quasar distant 12 billion light years from us, discovering that it is the brightest object ever observed (in absolute terms). It is so extreme that even the sophisticated machine learning method used to find quasars failed to recognize it, mistaking it for a star and demonstrating that the Universe’s secrets can’t be unveiled by AI alone, but it still needs to work in close collaboration with humans.

📣 Using ESO's #VLT, astronomers have characterised a truly record-breaking #quasar! 1/

Discover more: https://t.co/5o52yuoUHy

Artist's impression by ESO/M. Kornmesser pic.twitter.com/7Nr8dd76dU
— ESO (@ESO) February 19, 2024

What is a quasar?

Discovered by the astronomer Maarten Schmidt in 1963, quasars (QUASi stellAR radio source) are extremely luminous active galaxy nuclei. At the telescope, they appear like stars, but their spectrum is strongly red-shifted due to their distance (they are extragalactic objects). These objects release huge amounts of energy, mainly in radio and infrared bands, unlike galaxies, which emit primarily in the optic one.

This artist’s impression shows the record-breaking quasar J059-4351, the bright core of a distant galaxy that is powered by a supermassive black hole. Using ESO’s Very Large Telescope (VLT) in Chile, this quasar has been found to be the most luminous object known in the Universe to date. The supermassive black hole, seen here pulling in surrounding matter, has a mass 17 billion times that of the Sun and is growing in mass by the equivalent of another Sun per day, making it the fastest-growing black hole ever known. — *Artist’s impression of the record-breaking quasar J0529-4351. Credits: ESO*

Astronomers believe that the engine powering quasars can be enormous black holes absorbing matter from accretion disks orbiting around them.
Around a million quasars have been cataloged in the Universe, and a group of astronomers decided to study the properties of the most luminous known up to now, called J0529-4351.

The case of J0529-4351

As said, quasars are fed by black holes. In particular, astronomers observed that the black hole feeding J0529-4351 has a mass comparable to that of 17 billion Suns and increases it by ~1 Sun per day (between 280 and 490 solar masses per year). These observations make the observed quasar the most extreme one known to date.

Growing black holes should spin up over time, but this would decrease their accretion rate, making it difficult to build up such massive objects within the age of the Universe. A possible explanation for their masses can be found in “chaotic accretion” with randomly changing orientation, a situation that would keep the black hole spin low and so leave the accretion rate unchanged.

Hunting for quasars

Finding quasars does not require very large telescopes, but it requires highly precise data. This is even more complicated if the research aims to find extreme objects of this kind. Confirming what has been said, the quasar J1144-4308 was recognized to be a quasar only in 2022, despite being imaged since the 19^th century.

Today, combinations of data from modern all-sky surveys (like the ones from the Gaia mission of ESA) and machine-learning models allow scientists to identify with high precision what is a quasar and what is a star in the Milky Way. The weak point of this strategy is that it can’t recognize extreme cases, like the one object of the study, because it would be different from the ones used to train the model. The machine-learning model, indeed, assigned J0529-4351 to be a Milky Way star with a probability of 99.98%, while a human astronomer would recognize it to be a quasar at first sight.

This image shows the region of the sky in which the record-breaking quasar J0529-4351 is situated. Using ESO’s Very Large Telescope (VLT) in Chile, this quasar has been found to be the most luminous object known in the Universe to date. This picture was created from images forming part of the Digitized Sky Survey 2, while the inset shows the location of the quasar in an image from the Dark Energy Survey. — *Wide-field of the region around the quasar J0529-4351. Credits: ESO*

Scientists, to understand that what they were seeing was the brightest quasar ever observed, needed extremely precise data, a requirement that the X-shooter spectrograph can satisfy. It is an instrument mounted on the ESO’s VLT in the Atacama Desert, working across a wide wavelength range, from the ultraviolet to the near-infrared.

The importance of quasars

J0529-4351 will be studied a lot in the future to know more deeply its secrets. This will be done with the Very Large Telescope Interferometer (VLTI) when the GRAVITY instrument is upgraded. It will be able to image fainter and more remote astronomical objects than ever before, allowing it to measure the black holes’ mass with a high accuracy. This quasar will also be a target of the ELT (Extremely Large Telescope) of the ESO, currently under construction in the Atacama Desert.

In mid-August 2010 ESO Photo Ambassador Yuri Beletsky snapped this amazing photo at ESO’s Paranal Observatory. A group of astronomers were observing the centre of the Milky Way using the laser guide star facility at Yepun, one of the four Unit Telescopes of the Very Large Telescope (VLT). Yepun’s laser beam crosses the majestic southern sky and creates an artificial star at an altitude of 90 km high in the Earth's mesosphere. The Laser Guide Star (LGS) is part of the VLT’s adaptive optics system and is used as a reference to correct the blurring effect of the atmosphere on images. The colour of the laser is precisely tuned to energise a layer of sodium atoms found in one of the upper layers of the atmosphere — one can recognise the familiar colour of sodium street lamps in the colour of the laser. This layer of sodium atoms is thought to be a leftover from meteorites entering the Earth’s atmosphere. When excited by the light from the laser, the atoms start glowing, forming a small bright spot that can be used as an artificial reference star for the adaptive optics. Using this technique, astronomers can obtain sharper observations. For example, when looking towards the centre of our Milky Way, researchers can better monitor the galactic core, where a central supermassive black hole, surrounded by closely orbiting stars, is swallowing gas and dust. The photo, which was chosen as Astronomy Picture of the Day for 6 September 2010 and Wikimedia Picture of the Year 2010, was taken with a wide-angle lens and covers about 180 degrees of the sky. This image is available as a mounted image in the ESOshop. #L — *A laser beam from the VLT towards the Milky Way’s center. Credits: ESO*

Observing quasars, in general, allows astronomers also to study the origin of our Universe and its expansion. Their incredible distances, indeed, cause the light we see to represent what the Universe was billions of years ago. The aim of astronomers, based on this concept, is to understand if quasars are present in all galaxies sooner or later in their lifetime or are peculiar objects that characterize only some of them.

The hunt for quasars has just begun.