The galaxy is almost invisible, but its gravity gives it away:
While it is still considered a hypothetical theory, dark matter is being actively studied by scientists looking for novel cosmological clues. It does not interact with light or other types of electromagnetic radiation and can only be detected through its gravitational pull on nearby structures or the universe as a whole.
A team of astronomers led by David Li has recently confirmed the discovery of ten potential "dark galaxies," where starlight is so faint that it's extremely difficult to detect anything with traditional observatories. The new list also includes Candidate Dark Galaxy-2 (CDG-2), a celestial structure that might be composed of 99% dark matter and just 1% of normal matter.
CDG-2 was discovered by combining observations made through the Hubble Space Telescope, the Euclid space observatory, and the Hawaii-based Subaru Telescope. Li and his team at the University of Toronto were able to gain insight into the dark galaxy by looking for globular clusters, which are compact, spheroidal star formations that are closely bound together by gravity.
Thanks to Hubble's high-resolution cameras, the team was able to detect four different globular clusters in the Perseus galaxy cluster, 300 million light-years away from Earth. By combining further Euclid and Subaru observations, the researchers revealed a faint glow surrounding the clusters. This sparse light was coming from a nearby galaxy with extremely faint signs of starlight.
CDG-2 has a luminosity equivalent to one million Sun-like stars, with the four globular clusters making up 16% of its visible content. After using advanced statistical analysis, the astronomers speculate that 99% of all CDG-2's mass is just dark matter. Normal matter, including star-forming elements like hydrogen, was likely removed through gravitational interactions with nearby galaxies in the Perseus cluster.
While recent space telescopes like the JWST might provide unprecedented clues about the presence of dark matter in the local universe, studying and detecting the enigmatic substance continues to be an extremely complex research effort.
According to the study, there is "exceptionally strong" evidence of CDG-2's galactic nature. This is the first galaxy detected by just looking at the nearby globular clusters, and is likely one of the most dark matter-dominated galaxies ever detected. Globular clusters feature extremely high stellar densities that protect them from gravitational tidal disruption, and they are also considered a reliable indicator of "ghost" galaxies like CDG-2.
Journal Reference: Dayi (David) Li et al 2025 ApJL 986 L18 https://doi.org/10.3847/2041-8213/adddab
(Score: 5, Interesting) by spiraldancing on Wednesday February 25, @06:43PM (5 children)
IANAn Astrophysicist, and of course, this is all interpretive, deductive, best-guesswork ... but this article may actually be understating the findings.
Wikipedia, and other articles, have put CDG-2 at 99.9+% dark matter...
> "It is one of the most dark matter dominated galaxies ever discovered, estimated to be comprised of between 99.94% and 99.98% dark matter."
https://en.wikipedia.org/wiki/CDG-2 [wikipedia.org]
Lets go exploring.
(Score: 3, Interesting) by corey on Wednesday February 25, @08:15PM (4 children)
I really should look into this more but I take it that dark matter is not made of atoms, so there are no elements (H,He,etc). So what is the composition then? Are there dark elements? Seems not?
(Score: 0) by Anonymous Coward on Wednesday February 25, @09:12PM
You can call the particles like you want. Suggestion: darkions.
(Score: 5, Informative) by PiMuNu on Thursday February 26, @10:02AM
> dark matter is not made of atoms
I am a physicist.
To our best understanding, atomic structure of dark matter is unlikely because we don't see any thermal light emission on any wavelength associated with the matter. Even cold stuff glows a bit at far infrared and we see no evidence of that. We see no evidence of dark matter absorbing light that comes from behind it.
If dark matter *is* matter, which seems the best fit to the evidence, then it has to be something that isnt regular atoms. In particular it has to be a form of matter that does not interact with light (photons). So what could it be? Well, there is a sort of particle that doesn't interact with photons, called a neutrino. We see them every day in particle detectors, the sun makes squillions of them during nuclear fusion for example. But neutrinos are very low mass and very fast moving, and that doesnt seem to fit with measurements of how this dark matter, if it is matter, behaves.
So physicists have a mystery. It isn't unprecedented. Of the four forces (weak, strong, electromagnetic/light, gravity) there is plenty of precedent for particles that interact with some forces but not others. Neutrinos only interact via weak force (and maybe gravity, I'm not sure if that has been checked). Electrons and similar particles don't interact via strong force. Most particles interact via gravity but with wildly different coupling (mass). Protons and neutrons interact via all the forces.
If there is a particle out there that only interacts via gravity, we probably cant see it in the lab and only see it in astrophysical measurements like these. That's a bit unsatisfying because we have to make inferences, but the universe was (probably) not made to satisfy human curiosity. Maybe that's just the way it is.
Another possibility that is being chased is that we got gravity wrong. That's an interesting idea as well, but so far no one has got an alternative that fits the data. But we should keep chasing there as well. There is some data that hints that the particle physics explanation is wrong; if we study the behaviour of binary stars with very large separations, orbital periods that are thousands of earth years long, then they don't match the rotation period that we expect even with the dark matter model. But these star systems are quite rare and it is hard to build a big catalogue with good measurements of the rotational speed (the period is too long, we can only measure the speed of stars relative to each other and then guess the rotation period).
So it's a mystery! But fun to chase it down.
(Score: 2) by Freeman on Thursday February 26, @05:13PM (1 child)
Call it particle-X, because you're trying to solve for x. What is it? Beats them.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by turgid on Saturday February 28, @07:49PM
It's really difficult to observe something that doesn't radiate. This "dark matter" stuff only appears to interact gravitationally, and we've only just (2-3 decades) started to be able to detect gravitational radiation (gravity waves) and only at very specific frequency ranges. Their amplitudes are very low, hence the difficulty of detection.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].