The recently discovered dark galaxy candidates, particularly Candidate Dark Galaxy-2 (CDG-2), are primarily composed of dark matter and emit minimal light. This intriguing object features four globular clusters and is part of the Perseus galaxy cluster. The identification of CDG-2 presents significant implications for astronomers’ understanding of galaxy formation and evolution within the cosmic web, offering fresh insights into dark matter—an elusive substance that significantly outweighs ordinary matter yet remains invisible.
CDG-2 (dashed red circle) showcases its dominance in dark matter with only a sparse scattering of stars. Image credit: NASA/ESA/Dayi Li, Toronto/Joseph DePasquale, STScI.
“In the expansive fabric of the universe, most galaxies emit brilliant light across cosmic time and space,” stated University of Toronto astronomer David Lee and his research team.
“However, a rare subset of galaxies remains mostly hidden: those with low surface brightness, primarily dominated by dark matter and containing only a sparse collection of faint stars.”
“Detecting dark galaxies of this nature poses significant challenges.”
Dr. Li and his collaborators employed advanced statistical techniques to uncover 10 previously known galaxies with low surface brightness, in addition to identifying two new dark galaxy candidates by analyzing concentrated groupings of globular clusters.
These clusters may reveal the existence of faint stellar populations that are not easily observed.
To validate one of the dark galaxy candidates, they utilized NASA/ESA’s Hubble Space Telescope, ESA’s Euclid Space Observatory, and the ground-based Subaru Telescope in Hawaii.
High-resolution images captured by Hubble unveil four globular clusters closely packed within the Perseus Cluster—a large galaxy cluster located approximately 240 million light-years away in the constellation Perseus.
Further follow-up surveys using Hubble, Euclid, and Subaru revealed a faint, diffuse glow surrounding the cluster, providing compelling evidence of the underlying galaxy.
“This marks the first detection of a galaxy identified solely through its globular cluster population,” remarked Dr. Lee.
“Under conservative assumptions, these four clusters represent the entirety of the CDG-2 globular cluster.”
Preliminary assessments indicate that CDG-2 possesses brightness equivalent to about 6 million Sun-like stars, with globular clusters constituting 16% of its visible content.
Remarkably, approximately 99% of its mass is believed to be dark matter, encompassing both visible and dark constituents.
Much of the normal matter that facilitates star formation may have been stripped away due to gravitational interactions with neighboring galaxies in the Perseus cluster.
“CDG-2 stands out as the most globular cluster-dominated galaxy and may be among the most dark matter-dominated galaxies ever discovered,” the astronomers concluded.
Read their research paper published in June 2025. Astrophysics Journal Letter.
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Dai (David) Lee et al. 2025. Dark galaxy candidate-2: Verification and analysis of nearly dark galaxies in the Perseus cluster. APJL 986, L18; doi: 10.3847/2041-8213/adddab
Source: www.sci.news
