Astronomers Observe Extraordinary Accretion Event in Distant Galaxy
An artist’s impression of a black hole accretion. Image credit: John A. Paice.
AT2021lwx was first detected in 2020 by the Zwicky Transient Facility, and was subsequently detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS).
It took place nearly 8 billion years ago, when the Universe was around 6 billion years old, in the constellation of Vulpecula.
The explosion has so far lasted for more than three years, compared to most supernovae which are only visibly bright for a few months.
The only things in the Universe that are as bright as AT2021lwx are quasars — supermassive black holes with a constant flow of gas falling onto them at high velocity.
“With a quasar, we see the brightness flickering up and down over time,” said University of Southampton’s Professor Mark Sullivan.
“But looking back over a decade there was no detection of AT2021lwx, then it suddenly appeared as one of the most luminous things in the universe, which is unprecedented.”
Professor Sullivan and colleagues investigated AT2021lwx with several different telescopes: NASA’s Neil Gehrels Swift Observatory, ESO’s New Technology Telescope in Chile, and the Gran Telescopio Canarias in La Palma, Spain.
The researchers believe that the explosion is a result of a vast cloud of gas, possibly thousands of times larger than our Sun, that has been violently disrupted by a supermassive black hole.
Fragments of the cloud would have been swallowed up, sending shockwaves through its remnants, as well as into a large dusty doughnut-shaped formation surrounding the black hole. Such events are very rare and nothing on this scale has been witnessed before.
The physical size of the explosion was about 100 times larger than the entire Solar System, and at its brightest, it was about 2 trillion times brighter than the Sun.
There are different theories as to what could have caused such an explosion, but the study authors believe the most feasible explanation is an extremely large cloud of hydrogen gas or dust that has strayed from its orbit around the black hole and has been pulled in towards the center of the system.
They are now setting out to collect more data on the explosion — observing the object in different wavelengths, including X-rays, which could reveal the object’s temperature and what processes might be taking place at the surface.
They will also carry out upgraded computational simulations to test if these match their theory of what caused the explosion.
“We came upon this by chance, as it was flagged by our search algorithm when we were searching for a type of supernova,” said Dr. Philip Wiseman, an astronomer at the University of Southampton.
“Most supernovae and tidal disruption events only last for a couple of months before fading away.”
“For something to be bright for two plus years was immediately very unusual.”
Source: Sci News