Astronomers are focusing their attention on the massive feeding processes of massive black holes.


Artist's impression of a black hole causing tidal damage. (NRAO/AUI/NSF, Sophia Dagnello)

The more we learn about the Universe, the more possible it becomes that each galaxy revolves around a celestial colossus - a supermassive black hole that powers the galactic nucleus.

There's a lot we don't know about these massive artifacts, including how they grow so big, but new research might help us fill in some of the gaps. Any supermassive black hole in a galactic nucleus devours matter, according to a recent radio survey of all the galaxies in a region of the sky, but they go about it a little differently.

More and more evidence is accumulating that all galaxies have large black holes at their cores. According to astronomer Peter Barthel, these must have risen to their current mass.

It seems that, as a result of our findings, we now have a clearer picture of these growth mechanisms and are slowly but steadily learning more about them.

We're missing a crucial piece of the puzzle of how supermassive black holes shape and evolve because of a strange difference in the mass spectrum of black holes. Just 142 times the mass of the Sun has been observed in stellar mass black holes (those created by the collapsing center of a massive star), and even that one was heavier than normal, the result of a collision between two smaller black holes.

The mass of supermassive black holes, on the other hand, ranges from a few millions to billions of solar masses. You'd assume that if supermassive black holes grew from stellar mass black holes, there would be plenty of intermediate mass black holes out there, but there have been few detections.

One way to try to find it out is to look at the black holes we've discovered to see if their activity can provide any clues; this is exactly what a group of astronomers led by Jack Radcliffe of the University of Pretoria in South Africa did.

Their emphasis was on the GOODS-North area of space, which is located in the constellation Ursa Major. This area has been well researched, but only in visual, ultraviolet, and infrared wavelengths, thanks to a Hubble deep sky survey.

Radcliffe and his colleagues analyzed the area using a variety of wavelengths from visible to X-ray, as well as radio measurements using very long baseline interferometry. They were able to identify active galactic nuclei that were light in various wavelengths, indicating that they contained an active supermassive black hole.

Each dot represents a galaxy in this section of GOODS North. (NASA/ESA/G. Illingworth/P. Oesch/R. Bouwens/I. Labbé, as well as the Science Team)

As supermassive black holes deliberately accrete material by slurping gas and dust from their surroundings, the material heats up and glows brightly enough to be seen through large interstellar distances.

Any wavelengths of this light can be stronger depending on how much dust is obscuring the galactic nucleus, so no single wavelength spectrum can be used to distinguish all active galactic nuclei in a patch of sky.

With this new knowledge, the team investigated the AGN in GOODS-North and made a number of observations.

The first was that successful accretion isn't all created equal. That might seem obvious, because we have seen various supermassive black holes accreting at different rates, but the information is still useful. Some active supermassive black holes devour material at a much faster pace than others, while others don't consume much at all, according to the researchers.

They then looked for starburst activity, which is described as a region and time of intense star formation that coincides with an active galactic nucleus.

Feedback from an active galactic nucleus is thought to suppress star formation by blowing away all of the material that stars are made of, although some experiments have shown that the reverse can also happen: material shocked and compressed by feedback can collapse into baby stars.

They discovered that starburst behavior occurs in some galaxies but not in others. Interestingly, ongoing starburst activity can obscure an active galactic nucleus, implying that further research is needed to better define the role of feedback in quenching.

Finally, they looked at how relativistic jets would emerge from a supermassive black hole's poles during active accretion. These jets are believed to be made up of a small fraction of material that is funneled through magnetic field lines from the accretion disk's inner region to the black hole's poles, where it is blasted into space in the form of ionized plasma jets at speeds beyond the speed of light.

We don't know exactly how and why these jets shape, and the team's research indicates that the rate of material accretion isn't a major factor. They discovered that jets form only on rare occasions, and that the speed at which a black hole consumes mattered little.

According to the researchers, this knowledge may aid in a better understanding of supermassive black hole accretion behavior and development. It also shows that radio astronomy will play a bigger role in these studies in the future, they said.

Which means we'll have a stronger toolkit in the future to try to solve one of the most perplexing black hole mysteries: where do supermassive chonkers come from.

The team's research has been published and accepted in two papers in Astronomy & Astrophysics. They can be found here and here.


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