Astronomers Think They've Spotted a Galaxy That's 99.9% Dark Matter (cnn.com)
(Saturday March 07, 2026 @05:16PM (EditorDavid)
from the dark-side-of-the-dark dept.)
- Reference: 0180922892
- News link: https://science.slashdot.org/story/26/03/07/0753224/astronomers-think-theyve-spotted-a-galaxy-thats-999-dark-matter
- Source link: https://www.cnn.com/2026/03/03/science/nasa-hubble-galaxy-dark-matter
Astronomers have spotted a galaxy they believe is made of 99.9% dark matter, [1]reports CNN — and it's so faint, it's almost invisible:
> CDG-2, which is about 300 million light-years from Earth, appears to be so rich in dark matter that it could belong to a hypothesized subset of low surface brightness galaxies called "dark galaxies," which are believed to contain few or no stars.... [Post-doctoral astrophysics/statistics fellow Dayi Li at the University of Toronto was lead author on [2]a study about the discovery , and tells CNN] There is no strict definition of dark galaxies... but their existence is predicted by dark matter theories and cosmological simulations. "Where exactly do we draw the line in terms of how many stars they should have is still ambiguous, because not everything in astronomy is as clear-cut as we like," he said. "To be technically correct, CDG-2 is an almost-dark galaxy. But the importance of CDG-2 is that it nudges us much closer to getting to that truly dark regime, while previously we did not think a galaxy this faint could exist."
>
> To observe CDG-2, the researchers used data from three telescopes — Hubble, the European Space Agency's Euclid space observatory and the Subaru Telescope in Hawaii — along with a novel approach that involved looking for objects called globular clusters. "These are very tight, spherical groupings of very olds stars, basically the relics of the first generation of star formation," Li said. Globular clusters are bright even if the surrounding galaxy is not, and [3]previous observations have shown a relationship between them and the presence of dark matter in a galaxy, Li added. Because CDG-2 appears to have very few stars, there must be something else providing the mass that the clusters need to hold themselves together. Li and his colleagues assume that the source of the mass is dark matter.
>
> The researchers found a set of four globular clusters in the [4]Perseus Cluster , a group of thousands of galaxies immersed in a cloud of gas and one of the most massive objects in the universe. Further observations revealed a glow or halo around the globular clusters, suggesting the presence of a galaxy... Astronomers believe, Li explained, that after the formation of the clusters early in the galaxy's existence, larger surrounding galaxies stripped it of the hydrogen gas required to make more individual stars like our sun. "The material that this galaxy needed to continue to form stars was no longer there, so it was left with basically just a dark matter halo and the four globular clusters." The process, he added, would leave behind a skeleton or ghost of "a galaxy that pretty much just failed." As a result of this formation mechanism, the galaxy only has 0.005% of the brightness of our own galaxy, Li said...
>
> Studying potential dark galaxies is important because they provide nearly pristine views of the behavior of dark matter, according to Neal Dalal, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, who was not involved with the study.
Robert Minchin, an astronomer at New Mexico's National Radio Astronomy Observatory, told CNN that "it seems likely that other very dark galaxies will be found by this method in the future."
[1] https://www.cnn.com/2026/03/03/science/nasa-hubble-galaxy-dark-matter
[2] https://iopscience.iop.org/article/10.3847/2041-8213/adddab/meta
[3] https://academic.oup.com/mnras/article/472/3/3120/4093855
[4] https://www.nasa.gov/image-article/massive-perseus-cluster/
> CDG-2, which is about 300 million light-years from Earth, appears to be so rich in dark matter that it could belong to a hypothesized subset of low surface brightness galaxies called "dark galaxies," which are believed to contain few or no stars.... [Post-doctoral astrophysics/statistics fellow Dayi Li at the University of Toronto was lead author on [2]a study about the discovery , and tells CNN] There is no strict definition of dark galaxies... but their existence is predicted by dark matter theories and cosmological simulations. "Where exactly do we draw the line in terms of how many stars they should have is still ambiguous, because not everything in astronomy is as clear-cut as we like," he said. "To be technically correct, CDG-2 is an almost-dark galaxy. But the importance of CDG-2 is that it nudges us much closer to getting to that truly dark regime, while previously we did not think a galaxy this faint could exist."
>
> To observe CDG-2, the researchers used data from three telescopes — Hubble, the European Space Agency's Euclid space observatory and the Subaru Telescope in Hawaii — along with a novel approach that involved looking for objects called globular clusters. "These are very tight, spherical groupings of very olds stars, basically the relics of the first generation of star formation," Li said. Globular clusters are bright even if the surrounding galaxy is not, and [3]previous observations have shown a relationship between them and the presence of dark matter in a galaxy, Li added. Because CDG-2 appears to have very few stars, there must be something else providing the mass that the clusters need to hold themselves together. Li and his colleagues assume that the source of the mass is dark matter.
>
> The researchers found a set of four globular clusters in the [4]Perseus Cluster , a group of thousands of galaxies immersed in a cloud of gas and one of the most massive objects in the universe. Further observations revealed a glow or halo around the globular clusters, suggesting the presence of a galaxy... Astronomers believe, Li explained, that after the formation of the clusters early in the galaxy's existence, larger surrounding galaxies stripped it of the hydrogen gas required to make more individual stars like our sun. "The material that this galaxy needed to continue to form stars was no longer there, so it was left with basically just a dark matter halo and the four globular clusters." The process, he added, would leave behind a skeleton or ghost of "a galaxy that pretty much just failed." As a result of this formation mechanism, the galaxy only has 0.005% of the brightness of our own galaxy, Li said...
>
> Studying potential dark galaxies is important because they provide nearly pristine views of the behavior of dark matter, according to Neal Dalal, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, who was not involved with the study.
Robert Minchin, an astronomer at New Mexico's National Radio Astronomy Observatory, told CNN that "it seems likely that other very dark galaxies will be found by this method in the future."
[1] https://www.cnn.com/2026/03/03/science/nasa-hubble-galaxy-dark-matter
[2] https://iopscience.iop.org/article/10.3847/2041-8213/adddab/meta
[3] https://academic.oup.com/mnras/article/472/3/3120/4093855
[4] https://www.nasa.gov/image-article/massive-perseus-cluster/
Yesterday (Score:2)
by PPH ( 736903 )
Yesterday, upon the stair,
I met a man who wasn't there!
He wasn't there again today,
I wish, I wish he'd go away!
Dark matter = Suspense Account (Score:1)
by NewID_of_Ami.One ( 9578152 )
Typically Dark matter is the equivalent of suspense account in accounting - when your accounts donâ(TM)t balance you put the difference as a suspense account meaning we donâ(TM)t know what happened to this amount of money but are trying to find out
Saying you found anything related to dark matter is like saying you found your balance sheet doesnâ(TM)t balance.
But here the summary seems to equate it to faint and faintly visible stuff too apart from actual unknown/invisible/missing matter - whic
This constant assumption that dark matter is right (Score:2)
bothers me.
There is an unexplained phenomena and this "dark matter" and "dark energy" is just a made up explanation for that. There is no evidence it exists. No experiments we've done show that it exists and as far as I know there aren't even any proposed experiments that just need funding that are likely to show it exists.
Saying a galaxy is 99.9% something that we have no clue if even exists seems insane.
It's like string theory. Just made up stuff that is just tuned as needed to match measurements.
Re: (Score:3)
The "dark" nomenclature just marks the edge of where our experimental apparatus can no longer function. They know that dark matter exists, because there isn't enough regular matter to create enough gravity to keep a spinning galaxy like the Milky Way from flying apart. They can also see gravitational lensing occurring where one galaxy is behind another, but the closer galaxy doesn't have enough gravity from regular matter to bend light that much.
Dark energy is more if-fy, but they're pretty sure there is
Re: (Score:2)
You mean that you just don't believe in any measurement that is not made directly using the electromagnetic field.
If there are measurements made via the gravitational field, you don't believe it unless somebody figures out how to replicate the measurement directly using electromagnetism. If there is a physical phenomenon in this universe that simply never interacts with the electromagnetic field, well then it just will never exist for you.
Re: (Score:2)
> "...is just a made up explanation for that. There is no evidence it exists."
The idea of dark matter is not that dark matter exists, it's that the dark matter theory is a placeholder used to explain the observations we see in the universe that are contrary to the physical understandings as we know them currently. The physicists are essentially saying there's a bunch of stuff we just can't explain, and dark matter is a concept that they refer to until we can finally figure out the bigger picture. It may be a while.
Re: (Score:2)
Just replace all statements of "dark matter" with "lots of block holes". There's probably far more black holes than visible stars. And not too surprisingly, there is some galaxies with an enormous amount more black holes.
Re: This constant assumption that dark matter is r (Score:2)
No, neither the block holes nor the black holes appear to be a valid explanation.
If they were, we'd be seeing a phenomenon called "gravitational microlensing" much more often than we do. This happens when the black hole passes in front of something from the background and that something flares up briefly as if someone has put a giant loupe in front of it.
Since we don't see these microlensing events all that often, the dark matter is likely made up of clouds of particles that interact very weakly with our wo
Re: (Score:2)
"It's like string theory. Just made up stuff " That's all of modern mathematics. Sometimes we verify that some equations do a damn fine job modeling bits and bobs of the Universe. The bit and bobs are out there, the math is in our heads.
So we create a mathematical theory of Dark Matter. You can just call it the Theory of Gravity. The theory is just made up and in our heads. Yet it does a damn fine job of explaining some bits and bobs of the Universe.
Once we have everything all figured out, we'll get back to
Re: This constant assumption that dark matter is r (Score:3)
Dark matter is a name for a class of phenomena that are only observable by their gravitational influence on other things.
If something isn't visible, it is invisible, that is, "dark".
If it has mass, it is matter.
Hence, "dark matter", until a better understanding and a better name appears.
Ok?
Here's a cookie and a glass of milk for you, calm down.
Re: (Score:2)
OK Einstein, propose an alternative explanation for the results that isn't weirder than dark matter/dark energy.