In the vast tapestry of the universe, most galaxies shine brightly across cosmic time and space. Yet a rare class of galaxies remains nearly invisible — low-surface-brightness galaxies dominated by dark matter and containing only a sparse scattering of faint stars.

One such elusive object, dubbed CDG-2, may be among the most heavily dark matter-dominated galaxies ever discovered. (Dark matter is an invisible form of matter that does not reflect, emit, or absorb light.) The science paper detailing this finding was published in The Astrophysical Journal Letters.

Detecting such faint galaxies is extraordinarily difficult. Using advanced statistical techniques, David Li of the University of Toronto, Canada, and his team identified 10 previously confirmed low-surface-brightness galaxies and two additional dark galaxy candidates by searching for tight groupings of globular clusters — compact, spherical star groups typically found orbiting normal galaxies. These clusters can signal the presence of a faint, hidden stellar population.

To confirm one of the dark galaxy candidates, astronomers employed a trio of observatories: NASA’s Hubble Space Telescope, ESA’s (European Space Agency) Euclid space observatory, and the ground-based Subaru Telescope in Hawaii. Hubble’s high-resolution imaging revealed a close collection of four globular clusters in the Perseus galaxy cluster, 300 million light-years away. Follow-up studies using Hubble, Euclid, and Subaru data then revealed a faint, diffuse glow surrounding the star clusters — strong evidence of an underlying galaxy.

“This is the first galaxy detected solely through its globular cluster population,” said Li. “Under conservative assumptions, the four clusters represent the entire globular cluster population of CDG-2.”