heic2605 \u2014 Science Release<\/p>\n
The elusive object dubbed CDG-2 may be composed of 99% dark matter<\/p>\n
18 February 2026<\/p>\n
Most galaxies in the nearby Universe are quite luminous, but some are so faint they\u2019re nearly invisible. Astronomers, using the NASA\/ESA Hubble Space Telescope in combination with other observatories, identified a galaxy that appears to be almost entirely dominated by dark matter with only a smattering of stars. The galaxy, known as Candidate Dark Galaxy-2 (CDG-2), appears to contain just four globular star clusters (compared to the Milky Way\u2019s 150-plus), and dimly shines with the light of only about 1 million Suns.<\/p>\n
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 \u2014 low-surface-brightness galaxies dominated by dark matter and containing only a sparse scattering of faint stars.<\/p>\n
One such elusive object, dubbed CDG-2, may be among the most heavily dark matter-dominated galaxies ever discovered. Dark matter<\/a> is an invisible form of matter that does not reflect, emit, or absorb light. The science paper detailing this finding was published<\/a> in The Astrophysical Journal Letters.<\/p>\n 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 \u2014 compact, spherical star groups typically found orbiting normal galaxies. These clusters can signal the presence of a faint, hidden stellar population.<\/p>\n To confirm one of the dark galaxy candidates, astronomers employed a trio of observatories: the Hubble Space Telescope<\/a>, ESA\u2019s Euclid space observatory<\/a>, and the ground-based Subaru Telescope<\/a> in Hawaii. Hubble\u2019s 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 \u2014 strong evidence of an underlying galaxy.<\/p>\n \u201cThis is the first galaxy detected solely through its globular cluster population,\u201d said Li. \u201cUnder conservative assumptions, the four clusters represent the entire globular cluster population of CDG-2.\u201d<\/p>\n Preliminary analysis suggests CDG-2 has the luminosity of roughly 1 million Sun-like stars, with the globular clusters accounting for 16% of its visible content. Remarkably, 99% of its mass, which includes both visible matter and dark matter, appears to be dark matter. Much of its normal matter to enable star formation (primarily hydrogen gas) was likely stripped away by gravitational interactions with other galaxies inside the Perseus cluster.<\/p>\n \u201cThe Euclid data clearly confirm the presence of the extremely faint, diffuse light of CDG-2, revealing the galaxy behind the globular clusters for the first time,\u201d says Francine Marleau from the Institute for Astro- and Particle Physics at the University of Innsbruck in Austria. \u201cThe Euclid images of the Perseus cluster demonstrate the mission\u2019s unique capability to detect new low-surface-brightness galaxies, including extremely faint ones, while also revealing their globular clusters, nuclear star clusters, internal structures, and surrounding environments.\u201d<\/p>\n Globular clusters possess immense stellar density and are gravitationally tightly bound. This makes the clusters more resistant to gravitational tidal disruption, and therefore reliable tracers of such ghostly galaxies.<\/p>\n More information<\/p>\n The Hubble Space Telescope is a project of international cooperation between ESA and NASA.<\/p>\n Links<\/p>\n Contacts<\/p>\n