Hubble Spots Nearly Invisible 'Dark Galaxy'
NASA's Hubble Space Telescope has spotted a galaxy, named CDG-2, that is composed of 99% dark matter. This makes it one of the most dark matter-dominated structures ever found and nearly invisible in normal light, offering a unique natural laboratory to study the universe's mysterious invisible components.
The discovery was pioneered by a team led by David Li of the University of Toronto, who used advanced statistical techniques to hunt for the galaxy indirectly. Instead of looking for faint starlight, they searched for tight groupings of globular clusters, which can act as signposts for a hidden, underlying stellar population. This makes CDG-2 the first galaxy to be detected solely through its globular cluster population. Confirmation required a trio of powerful observatories working in concert. The Hubble Space Telescope's high-resolution imaging first revealed a collection of four globular clusters in the Perseus galaxy cluster, located 300 million light-years from Earth. Subsequently, the ESA's Euclid space observatory and the Subaru Telescope in Hawaii detected the faint, diffuse glow of the galaxy surrounding these clusters. To put its structure in perspective, CDG-2 contains just four globular star clusters, which are dense, spherical collections of stars. Our own Milky Way galaxy, by comparison, has more than 150. The total brightness of CDG-2 is estimated to be equivalent to only about 1 million suns, with its four clusters accounting for 16% of that visible light. The galaxy's lack of stars is likely due to its violent neighborhood. Located within the dense Perseus galaxy cluster, it's theorized that gravitational interactions with other, larger galaxies stripped away most of CDG-2's hydrogen gas. This gas is the primary fuel required for star formation.
