The more we study the universe, the more likely it seems that each galaxy orbiting a cosmic colossus – a supermassive black hole that powers the galactic core.
There’s a lot we don’t know about these gigantic objects – including the blatant question of how they grow so enormously – but new research could help fill in some gaps. According to a new radio survey of all galaxies in part of the sky, each supermassive black hole in a galactic core devours matter, although they do it a little differently.
“We are getting more and more indications that all galaxies have massive black holes in their centers. They must of course have grown to their present mass,” said astronomer Peter Barthel of the University of Groningen in the Netherlands.
“It seems that, thanks to our observations, we now have these growth processes in sight and are slowly but surely beginning to understand them.”
There is a funny gap in the mass range of black holes, which means that we are missing an important piece of the puzzle about how supermassive black holes form and grow. Stellar-mass black holes – formed from the collapsed core of a massive star – have been detected only up to 142 times the mass of the Sun, and even that hole was more massive than normal, the product of a collision between two smaller black holes holes.
Supermassive black holes, on the other hand, are usually between a few million and billions of solar masses. You would think that if supermassive black holes grew out of stellar mass, there would be a lot of intermediate mass, but very few detections have been made.
One way we can try to find out is by studying the black holes to have detected, to see if their behavior can give us clues; that’s what a team of astronomers led by Jack Radcliffe from the University of Pretoria in South Africa did.
Their focus was an area of space known as GOODS-North, located in the constellation of Ursa Major. The subject of a Hubble deep sky survey, this area is well studied, but mainly in optical, ultraviolet and infrared wavelengths.
A section of GOODS North, each with a galaxy. (NASA / ESA / G. Illingworth / P. Oesch / R. Bouwens and I. Labbé, and the Science Team)
Radcliffe and his team performed analyzes of the region using a series of wavelengths to X-rays, adding very long baseline interferometry radio observations to the mix. For example, they identified active galactic nuclei – those with an active supermassive black hole – that were bright in different wavelengths.
When supermassive black holes are actively collecting material – slurping gas and dust from their surrounding space – the material heats up and glows with bright enough electromagnetic radiation to be seen over long cosmic distances.
Depending on how much dust is obscuring the galactic core, some wavelengths of this light may be stronger, so no wavelength range can be used to identify all the active galactic nuclei in a patch of heaven.
Equipped with this additional information, the team conducted a study of the AGN in GOODS North and made several observations.
The first was that not all active recruits are the same. That may seem like a no-brainer, and we’ve certainly seen several supermassive black holes grow up at different rates, but the data is still useful. The researchers found that some active supermassive black holes devour material much faster than others, and some don’t devour much at all.
They then examined the presence of starburst activity – that is, a region and period of intense star formation – coinciding with an active galactic nucleus.
It is thought that feedback from an active galactic nucleus can quench star formation by blowing out all the material stars that make up stars, but some studies have shown that the opposite can also happen: that material that is shocked and compressed by feedback can collapse into baby stars.
They found that some galaxies have starburst activity and some don’t. Interestingly, sustained starburst activity can make an active galactic nucleus more difficult to see, suggesting that more research needs to be done to better define the role of feedback in extinction.
Finally, they studied the relativistic jets that can fire from the poles of a supermassive black hole during active growth. These jets are believed to be a small fraction of material that is conducted along magnetic field lines from the inner region of the accretion disk to the poles of the black hole, where it is blown into space in the form of jets of ionized plasma. , with speeds a. significant percentage of the speed of light.
We are not entirely sure how or why these jets form, and the team’s research suggests that the rate of material accumulation is not a major factor. They found that jets only occur occasionally and that it doesn’t matter whether a black hole eats quickly or slowly.
This information, the researchers said, could help better understand the accretion behavior and growth of supermassive black holes. And, they said, it also shows that radio astronomy may play a more important role in these studies in the future.
Which means we will have a more powerful toolset in the future to try and unravel one of the black hole’s most perplexing mysteries – where the hell do even supermassive chonkers come from?
The team’s research has been published and accepted in two articles in Astronomy and AstrophysicsThey can be found here and here.