A dim, lightweight galaxy on the outskirts of the Milky Way may be the smallest in the known universe, astronomers say.
Known as Segue 2, the dwarf galaxy consists of just 1,000 stars held together by a clump of dark matter. (By comparison, the Milky Way contains at least 100 billion stars.)
"Finding a galaxy this small is like finding an elephant smaller than a mouse," said James Bullock, a cosmologist at the University of California, Irvine, and an author of a paper on Segue 2 published in The Astrophysical Journal.
Segue 2, first discovered in 2009 as part of the Sloan Digital Sky Survey, is important for reasons other than size.
"For about 15 years, we have been predicting that galaxies like the Milky Way should be surrounded by thousands and thousands of low-mass clumps of dark matter" like the one at the center of Segue 2, Dr. Bullock said. Until now, even the smallest "clumps" detected by scientists were high mass -- at least a million times the mass of the sun.
At no more than 100,000 times the mass of the sun, Segue 2 "could be the first of these clumps detected that we've been predicting should be out there," Dr. Bullock said.
Until now, failure to find such clumps had puzzled astronomers. "It suggested there was some flaw in our theory of how the universe works," said Dr. Bullock, who was part of a team that used the powerful telescopes at the W. M. Keck Observatory in Hawaii to study the galaxy.
With this discovery, he said, there is hope that "this might be just be the tip of the iceberg."
This article originally appeared in The New York Times.