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Dark Matter Hunters Suspect They've Found 'Galaxy X'

Astronomers say they've found the signature of a dwarf satellite galaxy dominated by dark matter — a "Galaxy X" that they've been hunting for years.
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Years ago, astronomers mapped out curious ripples in the cold hydrogen gas that lies within the disk of our Milky Way galaxy — and suggested that the ripples were caused by the gravitational influence of an unseen dwarf galaxy dominated by dark matter. Now those astronomers say they may have found the lurker, nicknamed "Galaxy X."

The "observational confirmation" of the prediction is detailed in a research paper that's been accepted for publication in Astrophysical Journal Letters, astronomer Sukanya Chakrabarti of the Rochester Institute of Technology told NBC News in an email.

Chakrabarti and her colleagues analyzed near-infrared data collected by the European Southern Observatory's VISTA telescope to find four young stars clustered in the constellation Norma. The stars are Cepheid variables, which can be used as yardsticks for measuring astronomical distances. The research team determined that the stars are 300,000 light-years away, well beyond the edge of the Milky Way's disk.

"These young stars are likely the signature of this predicted galaxy," Chakrabarti said in a news release. She surmised that the dwarf satellite galaxy is hard to see because of our own Milky Way's obscuring dust, and because most of its mass consists of invisible (and mysterious) dark matter.

"The discovery of the Cepheid variables shows that our method of finding the location of dark-matter dominated dwarf galaxies works," she said. "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."



— Alan Boyle

In addition to Chakrabarti, the authors of "Clustered Cepheid Variables 90 Kiloparsec From the Galactic Center" include Roberto Saito, Alice Quillen, Felipe Gran, Christopher Klein and Leo Blitz.