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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