Astronomers Find 'Ghost Galaxy'
A Canadian-led team using Hubble Space Telescope data has discovered a "ghost galaxy" made almost entirely of dark matter. The object, which is nearly invisible in ordinary light, offers a rare opportunity to study dark matter's gravitational effects and challenges existing theories of galaxy formation.
The newly found galaxy, officially named Candidate Dark Galaxy-2 (CDG-2), was identified not by its starlight, but by the gravitational pull it exerts on four tightly-packed groups of very old stars known as globular clusters. This indirect detection method was necessary because the galaxy is almost completely invisible. Located approximately 300 million light-years away in the Perseus galaxy cluster, CDG-2 is estimated to be composed of more than 99% dark matter. The faint glow it does emit is equivalent to the light of about six million suns, a stark contrast to the 100 to 400 billion stars in our own Milky Way galaxy. Leading the research was David Li, a post-doctoral fellow at the University of Toronto. His team utilized archival data from the Hubble Space Telescope, with further confirmation from the European Space Agency's Euclid observatory and Japan's Subaru Telescope to spot the faint, diffuse light of the galaxy. The extreme lack of stars in CDG-2 suggests a turbulent past. Researchers theorize that long-ago encounters with larger neighboring galaxies stripped away the essential gas and material needed for star formation, leaving behind what Li describes as "only a skeleton of what it once was."
