The least massive galaxy in the known universe has been measured by UC Irvine scientists, clocking in at just 1,000 or so stars with a bit of dark matter holding them together.
The findings, made with the W. M. Keck Observatory and published today in The Astrophysical Journal, offer tantalizing clues about how iron, carbon and other elements key to human life originally formed. But the size and weight of Segue 2, as the star body is called, are its most extraordinary aspects. Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse," said UC Irvine cosmologist James Bullock, co-author of the paper. Astronomers have been searching for years for this type of dwarf galaxy, long predicted to be swarming around the Milky Way.
This image shows a standard prediction for the dark matter distribution within about 1 million light years of the Milky Way galaxy, which is expected to be swarming with thousands of small dark matter clumps called `halos'. The scale of this image is such that the disk of the Milky Way would reside within the white region at the center. Until now, there was no observational evidence that dark matter actually clumps this way, raising concerns that our understanding of the cosmos was flawed in a fundamental way. Observations of the ultra-faint galaxy Segue 2 (zoomed image) have revealed that it must reside within such a tiny dark matter halo, providing possibly the first observational evidence that dark matter is as clumpy as long predicted. Credit: Garrison-Kimmel, Bullock (UCI).