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Dark Galaxy Near Perseus Cluster (Compass Image)

Image labeled “CDG 2 near Perseus Cluster, HST ACS WFC”. 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. Compass arrows at lower left show east pointing to 1 o’clock and north pointing to 4 o’clock. A scale bar is labeled 36,000 light-years and 30 arcseconds. It extends about one-eighth of the way across the image. A color key shows F475W in blue, F814W in orange, and Euclid in gray.

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.

The scale bar is labeled in light-years along the top, which is the distance that light travels in one Earth-year. (It takes about 36,000 years for light to travel a distance equal to the length of the scale bar.) One light-year is equal to about 5.88 trillion miles or 9.46 trillion kilometers.

The scale bar is also labeled in arcseconds, which is a measure of angular distance on the sky. One arcsecond is equal an angular measurement of 1/3600 of one degree. There are 60 arcminutes in a degree and 60 arcseconds in an arcminute. (The full Moon has an angular diameter of about 30 arcminutes.) The actual size of an object that covers one arcsecond on the sky depends on its distance from the telescope.

The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above).

The color key shows which ACS filters were used when collecting the light. The color of each filter name is the visible-light color used to represent the light that passes through that filter.

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
    Science: NASA, ESA, Dayi Li (UToronto); Image Processing: Joseph DePasquale (STScI)

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Image labeled “CDG 2 near Perseus Cluster, HST ACS WFC”. 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. Compass arrows at lower left show east pointing to 1 o’clock and north pointing to 4 o’clock. A scale bar is labeled 36,000 light-years and 30 arcseconds. It extends about one-eighth of the way across the image. A color key shows F475W in blue, F814W in orange, and Euclid in gray.
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 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

Related Images & Videos

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 u201cCandidate dark galaxy - diffuse emission.u201d Four white dots are circled in blue and labeled globular clusters.

Dark Galaxy CDG-2 Near Perseus Cluster

The low-surface-brightness galaxy CDG-2, within the dashed red circle at right, is dominated by dark matter and contains only a sparse scattering of stars. The full image from NASA’s Hubble Space Telescope is at left.

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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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