"Dark Galaxy": Newly discovered galaxy consists of 99 percent dark matter
In the Perseus galaxy cluster, 300 million light-years away, a galaxy has been discovered that consists almost entirely of dark matter.
CDG-2 in an image from the Hubble Space Telescope, with the four globular clusters marked
(Image: NASA, ESA, D. Li (Utoronto), Image Processing: J. DePasquale (STScI))
An international research group has discovered a galaxy that shines with the brightness of about one million suns but consists of 99 percent dark matter. CDG-2 (Candidate Dark Galaxy-2) is likely one of the most dark matter-dominated galaxies ever discovered, the team explains. It was found solely thanks to its four globular clusters, which possibly make up its entire population. These alone are responsible for 16 percent of the entire galaxy's luminosity. Our Milky Way, in contrast, has more than 150 such stars clustered together in a spherical shape. Normally, one discovers the galaxy itself first and then its star clusters.
No material for star formation
After the globular clusters provided the crucial clue for the existence of the unusual galaxy, the research group conducted further analyses with the Hubble and Euclid space telescopes and the Subaru Telescope in Hawaii. This allowed them to detect the "faint, diffuse glow" surrounding the star clusters. This was interpreted as "strong evidence of an underlying galaxy." The investigations revealed that a large part of the matter from which stars normally form had likely been pulled out through interactions with other galaxies. This primarily involves hydrogen gas. The unusual object, consisting almost entirely of dark matter, remained.
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Dark matter is a form of matter not experimentally observed, which is intended to explain the measured movements of galaxies and galaxy clusters. It is assumed in science that there is significantly more dark matter in the cosmos than standard matter. Even more is attributed to the equally enigmatic dark energy. Even though both have not yet been observed, the theories are considered accepted because they answer fundamental questions. Nevertheless, alternative explanations are also put forward, and there are astronomical observations that do not fit with dark matter. Galaxies consisting mostly of dark matter have also been discovered, and CDG-2 is among the largest of them. The discovery is presented in The Astrophysical Journal Letters.
(mho)
