NASA’s Hubble spots nearly invisible “ghost galaxy” made of 99% dark matter

Science News from research organizations NASA’s Hubble spots nearly invisible “ghost galaxy” made of 99% dark matter A nearly invisible “ghost galaxy” made of 99% dark matter has been uncovered using star clusters as cosmic clues. Date: February 21, 2026 Source: NASA Hubble Mission Team Summary: Astronomers have uncovered one of the most mysterious galaxies ever found — a dim, ghostly object called CDG-2 that is almost entirely made of dark matter. Located 300 million light-years away in the Perseus galaxy cluster, it was discovered in an unusual way: not by its stars, but by four tightly packed globular clusters acting like cosmic breadcrumbs. Share: Facebook Twitter Pinterest LinkedIN Email FULL STORY The low-surface-brightness galaxy CDG-2, shown in this image from NASA's Hubble Space Telescope, is dominated by dark matter and contains only a sparse scattering of stars. This galaxy is nearly invisible, but by using advanced statistical techniques, scientists identified it by searching for tight groupings of stars called globular clusters. At left, the white box marks the area that was examined. At right is a magnified view of that area. The circle marked with a dashed red boundary indicates the location of the dark-matter dominated galaxy. Within the red, dashed circle are four globular clusters outlined by small, blue circles. Several background galaxies also appear within the red circle, but these are not related to the galaxy CDG-2. Credit: Image: NASA, ESA, Dayi Li (UToronto); Image Processing: Joseph DePasquale (STScI) Most galaxies blaze with billions of stars, lighting up the universe across vast distances. But a small and unusual group barely glows at all. These are low-surface-brightness galaxies, systems so faint they are difficult to detect and so sparse in stars that dark matter makes up most of their mass. One of these hidden objects, known as CDG-2, could rank among the most dark matter dominated galaxies ever identified. (Dark matter is an invisible form of matter that does not reflect, emit, or absorb light.) The discovery was reported in The Astrophysical Journal Letters.

How Astronomers Found CDG-2 Spotting galaxies this dim is extremely challenging. David Li of the University of Toronto, Canada, and his colleagues relied on advanced statistical analysis to search for clues. Instead of looking directly for faint starlight, they searched for tight groupings of globular clusters, which are dense, spherical collections of stars that typically orbit galaxies. These clusters can act as markers, hinting that a faint galaxy may be hiding nearby. Using this approach, the team identified 10 previously confirmed low-surface-brightness galaxies along with two additional dark galaxy candidates. Confirming the Galaxy With Hubble, Euclid, and Subaru To verify one of the candidates, astronomers turned to three powerful observatories: NASA's Hubble Space Telescope, ESA's (European Space Agency) Euclid space observatory, and the ground-based Subaru Telescope in Hawaii. High resolution images from Hubble revealed four closely packed globular clusters inside the Perseus galaxy cluster, located 300 million light-years from Earth. Further analysis combining data from Hubble, Euclid, and Subaru uncovered a faint, diffuse glow surrounding the clusters. That subtle halo of light provided strong evidence that an underlying galaxy was present. "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." A Galaxy Made Almost Entirely of Dark Matter Early measurements indicate that CDG-2 shines with the equivalent light of about 6 million Sun-like stars. Remarkably, the four globular clusters account for 16% of all the visible light in the galaxy. Even more striking, about 99% of the galaxy's total mass, including both visible matter and dark matter, appears to consist of dark matter. Much of the material normally needed to form stars, primarily hydrogen gas, was likely stripped away by gravitational interactions with other galaxies in the crowded Perseus cluster. Globular clusters themselves are extremely dense and tightly bound by gravity. Because of this, they are better able to withstand gravitational tidal disruption, making them dependable tracers of faint and ghostly galaxies like CDG-2. The Future of Dark Matter Galaxy Searches As large sky surveys continue to expand with missions such as Euclid, NASA's upcoming Nancy Grace Roman Space Telescope, and the Vera C. Rubin Observatory, researchers are increasingly using machine learning and sophisticated statistical tools to comb through enormous volumes of data.

The Hubble Space Telescope has now operated for more than 30 years and remains a cornerstone of astronomical discovery. It is a joint project between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, oversees the telescope and mission operations, with additional support from Lockheed Martin Space in Denver.

The Space Telescope Science Institute in Baltimore, operated by the Association of Universities for Research in Astronomy, manages Hubble's scientific operations for NASA. RELATED TOPICS Space & Time Space Exploration Space Telescopes NASA Galaxies Matter & Energy Aviation Telecommunications Nanotechnology Albert Einstein RELATED TERMS Globular cluster Dark matter Galaxy Open cluster Large-scale structure of the cosmos Dark energy Edwin Hubble Supergiant Story Source: Materials provided by NASA Hubble Mission Team. Note: Content may be edited for style and length. Related Multimedia: “Dark Galaxy” Identified by Hubble Space Telescope Journal Reference: Dayi (David) 大一 Li 李, Qing 青 Liu 刘, Gwendolyn M. Eadie, Roberto G. Abraham, Francine R. Marleau, William E. Harris, Pieter van Dokkum, Aaron J. Romanowsky, Shany Danieli, Patrick E. Brown, Alex Stringer.

Candidate Dark Galaxy-2: Validation and Analysis of an Almost Dark Galaxy in the Perseus Cluster.

The Astrophysical Journal Letters, 2025; 986 (2): L18 DOI: 10.3847/2041-8213/adddab Cite This Page: MLA APA Chicago NASA Hubble Mission Team. "NASA’s Hubble spots nearly invisible “ghost galaxy” made of 99% dark matter." ScienceDaily. ScienceDaily, 21 February 2026. . NASA Hubble Mission Team. (2026, February 21). NASA’s Hubble spots nearly invisible “ghost galaxy” made of 99% dark matter. ScienceDaily. Retrieved February 21, 2026 from www.sciencedaily.com/releases/2026/02/260221000307.htm NASA Hubble Mission Team. "NASA’s Hubble spots nearly invisible “ghost galaxy” made of 99% dark matter." ScienceDaily. www.sciencedaily.com/releases/2026/02/260221000307.htm (accessed February 21, 2026). Explore More from ScienceDaily RELATED STORIES Hidden Star Systems in the Milky Way Could Unlock the Secrets of Dark Matter Sep. 12, 2025 — For centuries, scientists have puzzled over globular clusters, the dense star systems that orbit galaxies without dark matter. Using ultra-detailed simulations, researchers recreated their origins ... ‘Bridge’ of Stray Stars Reveals Two Massive Galaxies Tearing Each Other Apart Aug. 6, 2025 — Astronomers have discovered a ghostly, million-light-year-long bridge of stars connecting two massive galaxies within the Abell 3667 cluster, 700 million light-years away. This glowing thread of ...

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