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Dark Galaxy CDG-2 Near Perseus Cluster

At left, a field of space with a dozen white foreground stars and a number of small, yellow background galaxies. An unremarkable area at center is outlined with a dashed red circle surrounded by a white box. Lines extend from the box to a pullout at right containing faint, grainy white light surrounded by a red circle labeled “Candidate dark galaxy – diffuse emission.” Four white dots are circled in blue and labeled globular clusters.

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.

About the Object

  • R.A. Position
    R.A. PositionRight ascension – analogous to longitude – is one component of an object's position.
    03:17:12.61
  • Dec. Position
    Dec. PositionDeclination – analogous to latitude – is one component of an object's position.
    +41:20:52.64
  • Constellation
    ConstellationOne of 88 recognized regions of the celestial sphere in which the object appears.
    Perseus
  • Distance
    DistanceThe physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs.
    About 245 million light-years
  • Dimensions
    DimensionsThe physical size of the object or the apparent angle it subtends on the sky.
    Image is 3.15 arcmin across (about 225,000 light-years)

About the Data

  • Data Description
    Data DescriptionProposal: A description of the observations, their scientific justification, and the links to the data available in the science archive.
    Science Team: The astronomers who planned the observations and analyzed the data. "PI" refers to the Principal Investigator.

    The Hubble observations include those from program 15235 (W. Harris)

  • Instrument
    InstrumentThe science instrument used to produce the data.
    ACS/WFC
  • Exposure Dates
    Exposure DatesThe date(s) that the telescope made its observations and the total exposure time.
    December 12, 2017
  • Filters
    FiltersThe camera filters that were used in the science observations.
    F475W, F814W
  • Object Name
    Object NameA name or catalog number that astronomers use to identify an astronomical object.
    Candidate Dark Galaxy near Perseus Cluster
  • Object Description
    Object DescriptionThe type of astronomical object.
    Low surface brightness galaxy
  • Release Date
    February 18, 2026
  • Science Release
    NASA’s Hubble Identifies One of Darkest Known Galaxies
    Read the release
  • Credit
    Image: NASA, ESA, Dayi Li (UToronto); Image Processing: Joseph DePasquale (STScI)

Downloads

  • Full Res (For Display), 3219 × 1330
    png (6.28 MB)
  • Full Res (For Print), 3219 × 1330
    tif (5.37 MB)
  • Full Res (JPG), 3219 × 1330
    jpg (1.1 MB)
  • 1999 × 826
    jpg (453.8 KB)
  • Unannotated - Full Res (For Display), 1886 × 1330
    png (4.12 MB)
  • Unannotated - Full Res (For Print), 1886 × 1330
    tif (3.79 MB)
  • Unannotated - Full Res (JPG), 1886 × 1330
    jpg (789.62 KB)
  • Unannotated, 2000 × 1410
    jpg (762.1 KB)
At left, a field of space with a dozen white foreground stars and a number of small, yellow background galaxies. An unremarkable area at center is outlined with a dashed red circle surrounded by a white box. Lines extend from the box to a pullout at right containing faint, grainy white light surrounded by a red circle labeled “Candidate dark galaxy – diffuse emission.” Four white dots are circled in blue and labeled globular clusters.
Color Info
Color InfoA brief description of the methods used to convert telescope data into the color image being presented.

These images were acquired by the ACS (Advanced Camera for Surveys) instrument on the Hubble Space Telescope. The color results from assigning different hues (colors) to a monochromatic (grayscale) image. In this case, the assigned colors are: Cyan: F475W, Orange: F814W

Compass and Scale
Compass and ScaleAn astronomical image with a scale that shows how large an object is on the sky, a compass that shows how the object is oriented on the sky, and the filters with which the image was made.

Related Images & Videos

Image labeled u201cCDG 2 near Perseus Cluster, HST ACS WFCu201d. At left is a field of space with an area outlined. At right is a blowup of the outlined area with four globular clusters circled.

Dark Galaxy Near Perseus Cluster (Compass Image)

This image of dark galaxy CDG-2 was captured by the Hubble Space Telescope’s ACS (Advanced Camera for Surveys) with additional data from the European Space Agency’s Euclid space mission. The image shows a scale bar, compass arrows, and color key for reference.

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Details

Last Updated
Feb 18, 2026
Location
NASA Goddard Space Flight Center
Contact
Media

Claire Andreoli
NASA’s Goddard Space Flight Center
Greenbelt, Maryland
claire.andreoli@nasa.gov

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