NASA's Hubble telescope has detected a possible 'dark galaxy', a discovery that could shed light on one of the universe's most elusive substances. The faint galaxy, named Candidate Dark Galaxy-2 (CDG-2), is believed to be composed of at least 99.9% dark matter, making it one of the most dark matter-heavy galaxies ever found. Dark matter, which is five times more abundant than regular matter, is invisible and has never been directly observed. However, its presence can be inferred through its gravitational effects on regular matter. The discovery of CDG-2, located about 300 million light-years from Earth, could help astronomers understand the behavior of dark matter. The galaxy appears to be so rich in dark matter that it could belong to a hypothesized subset of low surface brightness galaxies called 'dark galaxies', which are believed to contain few or no stars. The study, published in The Astrophysical Journal Letters, used data from three telescopes, including Hubble, the European Space Agency's Euclid space observatory, and the Subaru Telescope in Hawaii. The researchers found a set of four globular clusters in the Perseus Cluster, a group of thousands of galaxies immersed in a cloud of gas. Further observations revealed a glow or halo around the globular clusters, suggesting the presence of a galaxy. The process of forming a galaxy with few or no stars and mostly dark matter is believed to occur when larger surrounding galaxies strip away the hydrogen gas required to make more individual stars. This leaves behind a skeleton or ghost of 'a galaxy that pretty much just failed'. The galaxy only has 0.005% of the brightness of our own galaxy, making it incredibly faint. More observations are needed to detail the physical properties of CDG-2 and confirm how much dark matter it contains, which could be achieved by using the James Webb Space Telescope. Studying potential dark galaxies is important because they provide nearly pristine views of the behavior of dark matter. The discovery of CDG-2 could be a significant step towards understanding the true nature of dark galaxies and the role they play in the universe.
