Dark Matter Galaxy Discovery Confirmed
Astronomers have confirmed the existence of a galaxy composed almost entirely of dark matter, with what were thought to be four distinct star clusters now recognized as a single, nearly invisible system. This finding could reshape theories about how galaxies form and evolve in the universe. The discovery represents a significant breakthrough in understanding cosmic structure and dark matter distribution.
- The galaxy, named Dragonfly 44, is located in the Coma Cluster, approximately 300 million light-years from Earth. It is an ultra-diffuse galaxy, meaning it is as large as the Milky Way but has a hundred times fewer stars, making it very dim and difficult to observe. - Astronomers initially estimated Dragonfly 44's mass to be about a trillion times that of the Sun, similar to our own Milky Way, with 99.99% of it being dark matter. This was determined by measuring the high velocities of its stars using the Keck and Gemini North telescopes; the stars were moving too fast to be held together by the gravity of the visible matter alone. - The discovery was made by a team led by Pieter van Dokkum of Yale University using the Dragonfly Telephoto Array, which is specifically designed to find such faint and diffuse objects. - Later measurements of Dragonfly 44's rotation led to a revised mass estimate of about 160 billion solar masses, which is significantly less than the initial calculation but still implies a very high proportion of dark matter. - The hunt for dark matter began in the 1930s when astronomer Fritz Zwicky observed that galaxies in clusters were moving faster than their visible mass should allow, suggesting an unseen mass was providing extra gravitational pull. - In a separate, more recent discovery, another potential dark matter-dominated galaxy, designated CDG-2, was identified for the first time solely by detecting its surrounding population of globular star clusters. - The Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China is now being used to study dark matter in galaxies by detecting neutral hydrogen gas, which can provide more accurate measurements of a galaxy's total mass.
