NASA's Hubble Telescope Detects Possible 'Dark Galaxy'
Astronomers have discovered a galaxy so dim, it's almost invisible, shedding light on one of the universe's most enigmatic substances. The Hubble Space Telescope has revealed Candidate Dark Galaxy-2, or CDG-2, believed to be composed of at least 99.9% dark matter. If confirmed, CDG-2 would be among the most dark matter-rich galaxies ever found.
Dark matter, invisible and undetectable, constitutes five times more of the universe than regular matter. It's the invisible force that holds the universe together, inferred through its gravitational effects on visible matter. Most galaxies, including our Milky Way, are dominated by dark matter. However, some galaxies have an extreme ratio of dark to normal matter, resulting in sparse stars and a faint appearance, known as 'low surface brightness galaxies.'
CDG-2, located 300 million light-years away, is so rich in dark matter that it might belong to a hypothetical category of low surface brightness galaxies called 'dark galaxies,' which are thought to have few or no stars. Dayi Li, a post-doctoral fellow at the University of Toronto, explains that while low surface brightness galaxies emit some light, dark galaxies are at the extreme end, lacking faint light or typical galactic structures.
The definition of dark galaxies is not strict, but their existence is predicted by dark matter theories and simulations. CDG-2, being almost dark, nudges us closer to understanding the true nature of these galaxies. The discovery was made possible by data from Hubble, the European Space Agency's Euclid observatory, and the Subaru Telescope in Hawaii, along with a novel approach using globular clusters, which are tightly packed, spherical groups of ancient stars.
Globular clusters, even in faint galaxies, are bright and have been linked to dark matter in previous observations. CDG-2's sparse stars suggest that dark matter provides the necessary mass for these clusters to hold together. The researchers found four globular clusters in the Perseus Cluster, a massive collection of galaxies, and detected a glow around them, indicating a galaxy's presence.
The formation of CDG-2 is believed to involve the removal of hydrogen gas, essential for star formation, by larger surrounding galaxies early in its existence. This left CDG-2 with a dark matter halo and the four globular clusters, resulting in a galaxy with only 0.005% of the brightness of our galaxy. The discovery of CDG-2 opens up a new method for finding potentially dark galaxies by searching for globular clusters.
Neal Dalal, a researcher at the Perimeter Institute for Theoretical Physics, emphasizes the importance of studying dark galaxies for their nearly pristine views of dark matter behavior. Robert Minchin, an astronomer at the National Radio Astronomy Observatory, highlights the uniqueness of finding CDG-2 through globular clusters, despite the challenges of identifying dark galaxies.
However, confirming CDG-2 as a dark galaxy requires measuring its dark matter content, which is incredibly challenging due to its distance. Yao-Yuan Mao, an assistant professor of physics and astronomy, expresses excitement about the discovery, noting the faint light in Hubble images, which suggests a cohesive object rather than a random alignment of globular clusters.
The search for dark galaxies continues, with the potential to reveal more about the elusive nature of dark matter.
