A team of astronomers has identified a new galaxy that may be made completely of dark matter, the second of its kind.
In a discovery announced earlier this month, an international team of researchers has found a dark dwarf galaxy about 10 billion light years from Earth. In the current issue of Nature, the team of astronomers report having found one of the smallest galaxies on record, noting its mass is equal to just 113 million Suns. The galaxy is located halfway across the visible universe.
The newfound galaxy is incredibly distant and extremely small. It orbits as a satellite of a larger galaxy. Though telescopes cannot directly observe the dwarf galaxy, astronomers say they have detected its presence through the tiny distortions its gravity causes passing light. By using the gravitational lensing technique, researchers are often able to determine key characteristics of galaxies, including sizes, shapes and temperature.
The team noted that measurements of the temperature of the galaxy lead them to think it is largely comprised of dark matter.
“The existence of this low-mass dark galaxy is just within the bounds we expect if the universe is composed of dark matter that has a cold temperature. However, further dark satellites will need to be found to confirm this conclusion,” said scientists.
The team noted that they remain unsure of exactly what percentage of the galaxy’s mass is dark matter. Astronomers say that larger and more advanced telescopes are needed in order to understand exactly how dark matter and galaxies are related.
“It’s very hard to tell at the moment because the telescopes are just not powerful enough to see such dim galaxies so far away,” added Simona Vegetti, a Pappalardo Fellow in MIT’s Department of Physics and lead author of a paper on the work appearing in the latest online edition of Nature. “But [the dwarf galaxy] is most likely dominated by dark matter, or maybe there are a few stars hiding here and there.”
The discovery comes as astronomers have predicted that large-scale dark matter simulations of the Universe produce results that match the observed populations of large galaxies such as Milky Way. However, recent surveys show that there are far too many low-mass galaxies compared to what has been observed to warrant the existence of the galaxies observed.
One possible explanation is that at least some low-mass galaxies may be lacking much ordinary matter, say scientists. The team suggests that galaxies made up entirely of dark matter may be swirling about throughout the universe.
Dark matter is so named because it does not interact with light – it cannot be seen directly, as the stars and dust of the cosmos can. However, it does have mass – making up 85 percent of the mass in the Universe – and the effects of that mass can be spotted. Dark matter is widely believed to be composed primarily of a new, not yet characterized, type of subatomic particle. The search for this particle, by a variety of means, is one of the major efforts in particle physics today.
The researchers used the Keck-II Telescope in Hawaii to make their observations, taking advantage of a special piece of optics that provides sharp images of the sky. They plan to use the same method to look for more satellite galaxies in other regions of the universe, which they believe could help corroborate or challenge predictions of how dark matter behaves.
