Galaxy found to be made up almost entirely of dark matter

A prior study in 2009 predicted the galaxy's existence and location, and now new star data have confirmed it.
By Andrew McDonald | Feb 09, 2015
A team led by Sukanya Chakrabarti of the Rochester Institute of Technology (RIT) has discovered a group of young stars that might mark the location of a galaxy composed mostly of dark matter and obscured by dust clouds.

According to an RIT statement, Chakrabarti and team examined near-infrared data gathered by the European Southern Observatory's VISTA survey. While optical wavelengths of light are unable to reveal objects obscured by dust and gas, VISTA's near-infrared capability allows it to accrue information on stars and other bodies that reside along the plane of our Milky Way galaxy.

The VISTA data revealed four young stars located in the Norma constellation and near the galactic plane but, at about 300,000 light-years away, too distant to actually be part of the Milky Way. All four stars are Cepheid variables, a type of star useful to calculating distances. This group of stars are the most distant Cepheid variables situated near the galactic plane.

The detection of the four stars confirms a prediction put forth by Chakrabarti in 2009. She had analyzed perturbations in the outer disk of the Milky Way and hypothesized that a dwarf galaxy composed mainly of dark matter must be located near our galaxy. Thanks to the four Cepheid variables, Chakrabarti and colleagues were able to determine the distance to and location of this enigmatic galaxy, verifying her earlier hypothesis.

"The discovery of the Cepheid variables shows that our method of finding the location of dark-matter dominated dwarf galaxies works," Chakrabarti explained. "It may help us ultimately understand what dark matter is made up of. It also shows that Newton's theory of gravity can be used out to the farthest reaches of a galaxy, and that there is no need to modify our theory of gravity."

The paper describing the findings has been published online in the Astrophysical Journal Letters.

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