Editor’s Note: This post highlights a combination of peer-reviewed results and data from Webb science in progress, which has not yet been through the peer-review process.
As data from NASA’s James Webb Space
Telescope becomes public, researchers hunt its archives for unnoticed cosmic
oddities. While examining images from the COSMOS-Web survey, two researchers, Pieter
van Dokkum of Yale University and Gabriel Brammer of the University of
Copenhagen, discovered an unusual object that they nicknamed the Infinity
Galaxy.
It displays a highly unusual shape of
two very compact, red nuclei, each surrounded by a ring, giving it the shape of
the infinity symbol. The team believes it was formed by the head-on collision
of two disk galaxies. Follow-up observations showed that the Infinity Galaxy
hosts an active, supermassive black hole. What is highly unusual is that the
black hole is in between the two nuclei, within a vast expanse of gas. The team
proposes that the black hole formed there via the direct collapse of a gas cloud
– a process that may explain some of the incredibly massive black holes Webb
has found in the early universe.
The Infinity Galaxy, the result of two colliding
spiral galaxies, is composed of two rings of stars (seen as ovals at upper
right and lower left). The two nuclei of the spiral galaxies are seen
represented in yellow within the rings. Glowing hydrogen that has been stripped
of its electrons between the two galaxies appears green. Astronomers have
detected a million-solar-mass black hole that seems to be embedded within this
large swath of ionized gas. They suggest that the black hole might have formed
there through a process known as direct collapse. This image from NASA’s James
Webb Space Telescope’s NIRCam (Near-Infrared Camera) represents light at 0.9
microns as blue (F090W), 1.15 and 1.5 microns as green (F115W+F150W), and 2.0
microns as red (F200W).
NASA, ESA, CSA, STScI, P. van
Dokkum (Yale University)
Here Pieter van Dokkum, lead author of a
peer-reviewed paper describing their initial discovery and principal
investigator of follow-up Webb observations, explains why this object could be the best evidence yet for a novel
way of forming black holes.
“Everything is unusual about this
galaxy. Not only does it look very strange, but it also has this supermassive
black hole that’s pulling a lot of material in. The biggest surprise of all was
that the black hole was not located inside either of the two nuclei but in the
middle. We asked ourselves: How can we make sense of this?
“Finding a black hole that’s not in the
nucleus of a massive galaxy is in itself unusual, but what’s even more unusual
is the story of how it may have gotten there. It likely didn’t just arrive
there, but instead it formed there. And pretty recently. In other words, we
think we’re witnessing the birth of a supermassive black hole – something that
has never been seen before.
“How supermassive black holes formed is
a long-standing question. There are two main theories, called ‘light seeds’ and
‘heavy seeds.’ In the light seed theory, you start with small black holes
formed when a star’s core collapses and the star explodes as a supernova. That
might result in a black hole weighing up to about 1,000 Suns. You form a lot of
them in a small space and they merge over time to become a much more massive
black hole. The problem is, that merger process takes time, and Webb has found
incredibly massive black holes at incredibly early times in the universe –
possibly even too early for this process to explain them.
“The second possibility is the heavy
seed theory, where a much larger black hole, maybe up to one million times the
mass of our Sun, forms directly from the collapse of a large gas cloud. You
immediately form a giant black hole, so it’s much quicker. However, the problem
with forming a black hole out of a gas cloud is that gas clouds like to form
stars as they collapse rather than a black hole, so you have to find some way
of preventing that. It’s not clear that this direct-collapse process could work
in practice.
“By looking at the data from the
Infinity Galaxy, we think we’ve pieced together a story of how this could have
happened here. Two disk galaxies collide, forming the ring structures of stars
that we see. During the collision, the gas within these two galaxies shocks and
compresses. This compression might just be enough to form a dense knot, which
then collapsed into a black hole.
“There is quite a bit of circumstantial
evidence for this. We observe a large swath of ionized gas, specifically
hydrogen that has been stripped of its electrons, that’s right in the middle
between the two nuclei, surrounding the supermassive black hole. We also know
that the black hole is actively growing – we see evidence of that in X-rays
from NASA’s Chandra X-ray Observatory and radio from the Very Large Array. Nevertheless, the question
is, did it form there?
This image of the Infinity Galaxy from NASA’s James
Webb Space Telescope’s NIRCam is overlayed with a contour map of data from the
Very Large Array radio telescope. The center pinpoint of radio emission
perfectly lines up with the center of the glowing gas detected in the infrared
in between the two nuclei of the galaxies. The detection of radio emission from
supermassive black holes informs researchers about the energetics of the
object, specifically how it is pulling in surrounding material.
NASA, ESA, CSA, STScI, VLA, P.
van Dokkum (Yale University)
“There are two other possibilities that come to mind. First, it could be a
runaway black hole that got ejected from a galaxy and just happens to be
passing through. Second, it could be a black hole at the center of a third
galaxy in the same location on the sky. If it were in a third galaxy, we would
expect to see the surrounding galaxy unless it were a faint dwarf galaxy.
However, dwarf galaxies don’t tend to host giant black holes.
“If the black hole were a runaway, or if it were in an unrelated galaxy, we
would expect it to have a very different velocity from the gas in the Infinity
Galaxy. We realized that this would be our test – measure the velocity of the
gas and the velocity of the black hole, and compare them. If the velocities are
close, within maybe 30 miles per second (50 kilometers per second), then it
becomes hard to argue that the black hole is not formed out of that gas.
“We applied for and received director’s discretionary time to follow up on
this target with Webb, and our preliminary results are exciting. First, the
presence of an extended distribution of ionized gas in between the two nuclei
is confirmed. Second, the black hole is beautifully in the middle of the
velocity distribution of this surrounding gas – as expected if it formed there.
This is the key result that we were after!
“Third, as an unexpected bonus, it turns out that both galaxy nuclei also
have an active supermassive black hole. So, this system has three confirmed
active black holes: two very massive ones in both of the galaxy nuclei, and the
one in between them that might have formed there.
“We can’t say definitively that we have found a direct collapse black hole.
But we can say that these new data strengthen the case that we’re seeing a
newborn black hole, while eliminating some of the competing explanations. We
will continue to pore through the data and investigate these possibilities.”
About the Author
Pieter van Dokkum is a professor of astronomy and physics at Yale University. He is lead author on a paper about the Infinity Galaxy that has been accepted for publication by The Astrophysical Journal Letters, and principal investigator of Webb Director’s Discretionary program 9327.
Source: NASA’s Webb Finds Possible ‘Direct Collapse’ Black Hole - NASA Science
