NASA, ESA, D. Li (U. Toronto); J. DePasquale (STScI)
The low surface brightness galaxy CDG-2 is dominated by dark matter and contains only a sparse distribution of stars
In the vast tapestry of the Universe, most galaxies shine brightly. But a rare class of “low surface brightness” galaxies is nearly invisible. One of these elusive objects, called CDG-2, has just been identified. It is one of the most dark matter-dominated galaxies ever discovered.
Most galaxies in the nearby Universe are quite luminous, but some are so faint that are almost invisible.
A team of astronomers, using the NASA/ESA Hubble Space Telescope in combination with other observatories, has identified a galaxy that appears to be almost entirely dominated by dark matterand with only a small number of stars.
The galaxy, known as CDG-2 (Candidate Dark Galaxy-2), appears to contain just four globular clusterscompared to more than 150 in the Milky Way, and glows dimly with the light of only about 1 million suns.
In the vast tapestry of the Universe, most galaxies shine brightly in cosmic time and space. However, a rare class of galaxies remains almost invisible – low surface brightness galaxiesdominated by dark matter and containing only a sparse distribution of faint stars.
One of these elusive objects, called CDG-2, may be among the galaxies most dominated by dark matter ever discovered. Dark matter is an invisible form of matter that does not reflect, emit or absorb light. The scientific article describing this discovery was published in The Astrophysical Journal Letters.
Detecting such faint galaxies is extraordinarily difficult. Using advanced statistical techniques, David Lifrom the University of Toronto, Canada, and his team identified 10 low surface brightness galaxiesl previously confirmed and two more dark galaxy candidates, seeking intimate groupings of globular clusters – spherical, compact groups of stars that are typically orbiting normal galaxies.
These globular clusters may indicate the presence of a stellar population tenuous and hidden.
To confirm one of the dark galaxy candidates, astronomers used a trio of observatories: the Hubble Space TelescopeESA’s Euclid space observatory and the Subaru Telescope in Hawaii.
High-resolution Hubble images have revealed a close cluster of four globular clusters in the Perseus galactic cluster300 million light years away. Further studies using data from Hubble, Euclid and Subaru then revealed a faint, diffuse glow around the star clusters – a strong evidence for an underlying galaxy.
“This is the first galaxy detected only through its population of globular clusters,” Li said. “Under conservative assumptions, the four clusters represent the entire CDG-2 globular swarm population“.
Preliminary analyzes suggest that CDG-2 has a luminosity of about 1 million stars similar to the Sunwith globular clusters representing 16% of its visible content.
Notably, 99% of your masswhich includes both visible matter and dark matter, appears to be dark matter.
Much of its normal matter, which allows for star formation (mainly hydrogen gas), was likely eliminated by gravitational interactions with other galaxies within the Perseus galaxy cluster.
“Euclid data clearly confirm the presence of light extremely faint and diffuse image of CDG-2, revealing for the first time the galaxy behind the globular clusters”, says Francine Marleau from the Institute of Astrophysics and Particle Physics at the University of Innsbruck, Austria.
“The Euclid images of the Perseus cluster demonstrate the mission’s unique ability to detect new low-surface-brightness galaxies, including extremely faint galaxies, while revealing their globular clusters, nuclear star clusters, internal structures and surrounding environments,” he adds.
Globular clusters have a immense stellar density and are linked tightly by gravity. This makes the clusters more resistant to tidal gravitational perturbations and therefore reliable trackers of such ghostly galaxies.
