Astronomers have found a fascinating cosmic mystery: a galaxy mostly made of dark matter. This galaxy, located 300 million light-years away, has only four visible star clusters. They looked like isolated groups for a long time, but new studies show they are part of a bigger mystery.
Tentatively named Candidate Dark Galaxy-2 (CDG-2), this galaxy is unique because 99.9% of its mass is dark matter. Conventional matter makes up only 0.1%. According to a recent study in The Astrophysical Journal Letters, these star clusters contribute only 16% of the galaxy’s brightness, hinting at a much larger, invisible structure.
Using powerful tools like the Hubble, Euclid, and Subaru telescopes, scientists have identified a faint glow surrounding these clusters. This faint light reveals a hidden galaxy that is hard to see on its own. The study notes that CDG-2 has a total brightness similar to about 6 million suns, with its unusual composition indicating a dense dark matter halo.
Dark matter is a huge part of our universe, making up about 27% of its energy density and 85% of its total mass, yet we cannot see it. Scientists understand it mostly through its gravitational effects on stars and galaxies. For example, our Milky Way galaxy is thought to have a dark matter halo that forms around 90% of its mass.
CDG-2 stands out because it has so few visible stars. This hints at an exciting area of research: dark galaxies. These galaxies are becoming more prominent in astronomical studies, providing unique opportunities to understand dark matter and how galaxies form.
In May 2021, astronomers reported finding many potential dark galaxies, suggesting they are not as rare as once thought. This raises intriguing questions about galaxy evolution and encourages ongoing investigations into the hidden structures of the universe.
Discoveries like CDG-2 help us learn more about dark matter and its role. Understanding these mysterious galaxies could unlock more secrets about our universe’s composition and the forces that shape it.
For more details about the study, you can check the report published in The Astrophysical Journal Letters here.
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