Blazar: Why astronomers are gobsmacked at the discovery of a supermassive black hole

Astronomers are perplexed by the discovery of a supermassive black hole, a 'blazar', with a mass of 700 million suns, located in a galaxy approximately 12.9 billion light years away and firing a powerful energy beam directly at Earth.

This enigmatic supermassive blackhole, named VLASS J041009.05-013919.88 (J0410-0139 for short), thus represents a part of the early Universe, just about 800 million years after the Big Bang. It makes it the most distant and earliest 'blazar', or galaxy with a supermassive black hole at its centre, ever discovered.

A team of researchers led by Eduardo Bañados, a group leader at the Max Planck Institute for Astronomy, published their findings in December 2024 in The Astrophysical Journal Letters and Nature Astronomy. The research team used data from multiple telescopes, including the Atacama Large Millimetre Array, Magellan telescopes, and the European Southern Observatory's Very Large Telescope, all located in Chile, and NASA's Chandra Observatory in Earth orbit, to identify the blazar, its distance, and other characteristics.

Peering back in time

Light needs a certain amount of time to travel; therefore, seeing an object far out in the Universe implies that we are gazing back in time. Thus, when we gaze upon the Sun, we perceive it as it was eight minutes ago, the Moon almost 1.3 seconds ago, and the brightest star in the night sky, Sirius, 8.6 years ago.

Grey hair occur as we age; however, the presence of grey hair in infancy is unexpected. Similarly, the discovery of such a large supermassive black hole when the cosmos was so young is perplexing. In light of this, astronomers wonder if the discovery is a freak event or if we need to fundamentally alter our understanding of how supermassive black holes evolve.

What are blazars?

Astronomers recently discovered that they had been mistaking blazars, quasars, and radio galaxies as distinct celestial objects, but they are the same cosmic animal, similar to the parable of the blind people and the elephant, in which one identifies an elephant through touch, perceiving its legs as thick tree trunks, another mistaking its large, flapping ears for fans, the third feels the tail and thinks it is a rope, and the fourth touches the tusk and assumes it is a spear.

They are all Active Galactic Nuclei (AGN), which are made up of a supermassive black hole with a mass of millions or billions of times that of the Sun. The massive blackhole's powerful gravitational pull attracts matter from all directions. Like the Earth and other planets, these heated gaseous components swirl around the blackhole like a platter, known as an accretion disc. As they revolve faster, they become hotter and emit more energy across the electromagnetic spectrum, from radio waves to gamma rays. The AGN's high magnetic field concentrates these radiations on the poles, some bursting out into powerful jets.

As the black hole spins rapidly, the jets flash by like a lighthouse's searchlight. If we chance to be in the path of the jet's sweep, we will see intense radiation pulses striking us, the intensity of the radiation going up and down in a matter of hours or days. Blazers were the term used to describe such cosmic objects with jets pointed at us. Quasars are jets pointing in a different direction.

What is in the name?

VLASS stands for the ‘Very Large Array Sky Survey’, which aims to map roughly 80% of the radio sky with the Karl G. Jansky Very Large Array (VLA) radio telescope in the United States. The study, which began in September 2017, will scan and identify cosmic radio sources in every portion of the sky visible to the VLA, and astronomers estimate that approximately 10 million new objects will be discovered – four times what is already known. Each sky area will be scanned three times with a time interval to detect variations in the brightness and intensity of radio sources, allowing us to better grasp the dynamics of these elusive and enigmatic celestial objects.

Thus, VLASS is an acronym for The Very Large Array Sky Survey Catalogue. The J indicates that the angle measurement of the celestial position was made from the coordinate equinox of the year 2000. The remaining numbers in the name represent celestial coordinates, similar to how we identify a location on the Earth's surface using LatLong. In short, the name indicates to astronomers where the object is located in the sky.

Farthest blazar

The team sifted through the huge data provided by the VLASS to identify possible blazers from the distant past. The radio source of J0410−0139 was recognised as a deep-space blazer belonging to the infant stage of the Universe. "The alignment of J0410−0139's jet with our line of sight allows astronomers to peer directly into the heart of this cosmic powerhouse," says study co-author Emmanuel Momjian, an astronomer at the National Radio Astronomy Observatory in Virginia. "This blazar offers a unique laboratory to study the interplay between jets, black holes, and their environments during one of the universe's most transformative epochs," he added.

Astronomers have catalogued tens of thousands of AGNs through cosmic surveys, and the number is growing as observational techniques and technology evolve. However, fewer than 3000 of them are blazers, with the jets headed towards the Earth. Most of these blazers are closer to us, implying that they formed relatively recently in cosmic history. The previous record holder for the most distant blazar was PSO J0309+27, discovered in 2020 and located nearly 12.8 billion light-years from Earth. That implies the last holder record was 100 million years older than J0410−0139. 100 million years is sufficiently long for a supermassive black hole to grow by several orders of magnitude, hence the discovery of PSO J0309+27 earlier was not astonishing.

Enigma

J0410-0139 is not only the farthest discovered but also one of the earliest supermassive black holes to emerge in our Universe. The discovery calls into question scientists' present understandings of the early cosmos, particularly the formation and growth of black holes. Our assumptions about how huge they could get, how quickly they could develop, and how many may have existed have all been challenged.

Not all AGN line their jets with the Earth, so there must be hundreds or thousands more for every blazer identified with its jet pointing at us. "Imagine that you read about someone who has won $100 million in a lottery," Bañados said. "Given how rare such a win is, you can immediately deduce that there must have been many more people who participated in that lottery but have not won such an exorbitant amount. Similarly, finding one [quasar] with a jet pointing directly toward us implies that at that time, there must have been many [quasars] in that period of cosmic history with jets that do not point at us," he added.

An early universe teeming with hundreds of thousands of supermassive black holes challenges our existing understanding of cosmic evolution. "These observations are surprising because we don't seem to understand supermassive black hole formation as well as we thought," says Joe Pesce, NSF program director for the NSF National Radio Astronomy Observatory (NSF NRAO). "But they are also exciting because it's a new mystery that we have to solve, and in doing so, we will learn more about the universe and how it works", he added.

"Now, my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose," quipped J.B.S. Haldane, a British-born scientist who later moved to India and acquired Indian citizenship. Haldane was not far from true.