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5h ago

Astronomers Report Faint Perseus Galaxy That Appears Almost All Dark Matter

Scientists traced four globular clusters to a dim halo, unveiling a new way to spot nearly invisible galaxies.

This image from the European Space Agency's Euclid space telescope shows hundreds of thousands of galaxies and, at the center, the Perseus Cluster, a rich conglomerate of galaxies that also houses CDG-2.
Globular clusters are spherical agglomerates of stars bound together by gravity, like this one called ESO 591-12 or Palomar 8, photographed by Hubble.
The low-surface-brightness galaxy CDG-2, shown in this image from the NASA/ESA 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 the centre of this image. The Hubble observations include those from programme 15235 (W. Harris). [Image description: A field of space with a dozen white foreground stars and a number of small, yellow background galaxies.]
Image

Overview

  • The peer‑reviewed study by Dayi Li and colleagues in The Astrophysical Journal Letters details Candidate Dark Galaxy‑2 about 300 million light‑years away in the Perseus Cluster.
  • Using Hubble, ESA’s Euclid and the Subaru Telescope, the team identified four tightly grouped globular clusters and stacked deep images to reveal an ultrafaint diffuse galaxy around them.
  • Imaging indicates the system is overwhelmingly dark‑matter dominated—estimated at roughly 99% or more—with total starlight equivalent to about six million Suns (around 0.005% of the Milky Way).
  • The authors say this is the first galaxy detected solely through its globular cluster population, highlighting a method that could uncover more almost‑dark systems.
  • Researchers emphasize that confirming the dark‑matter fraction and internal dynamics requires spectroscopic and kinematic follow‑up, potentially with the James Webb Space Telescope.