Dark Energy Survey Finds Eight More Galactic Neighbours

Satellite galaxies are small celestial objects that orbit larger galaxies, such as our own Milky Way. Dwarf galaxies can be found with fewer than 1,000 stars, in contrast to the Milky Way, an average-size galaxy containing billions of stars. Scientists have predicted that larger galaxies are built from smaller galaxies, which are thought to be especially rich in dark matter, the substance that makes up about 25 percent of the total matter and energy in the universe. Dwarf satellite galaxies, therefore, are considered key to understanding dark matter and the process by which larger galaxies form.

The main goal of the Dark Energy Survey (DES), as its name suggests, is to better understand the nature of dark energy, the mysterious stuff that makes up about 70 percent of the matter and energy in the universe. Scientists believe that dark energy is the key to understanding why the expansion of the universe is speeding up. To carry out its dark energy mission, DES takes snapshots of hundreds of millions of distant galaxies. However, some of the DES images also contain stars in dwarf galaxies much closer to the Milky Way. The same data can therefore be used to probe both dark energy, which scientists think is driving galaxies apart, and dark matter, which is thought to hold galaxies together.

Scientists can only see the faintest dwarf galaxies when they are nearby, and had previously found only a few. If these new discoveries are representative of the entire sky, there could be many more galaxies hiding in our cosmic neighbourhood.”Just this year, more than 20 of these dwarf satellite galaxy candidates have been spotted, with 17 of those found in Dark Energy Survey data,” said Alex Drlica-Wagner of the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “We’ve nearly doubled the number of these objects we know about in just one year, which is remarkable.”  See more on The Fermi National Accelerator Laboratory Press Release

Summary: 
The Dark Energy Survey has now mapped one-eighth of the full sky (red shaded region) using the Dark Energy Camera on the Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile (foreground). This map has led to the discovery of 17 dwarf galaxy candidates in the past six months (red dots), including eight new candidates just announced. Several of the candidates are in close proximity to the two largest dwarf galaxies orbiting the Milky Way, the Large and Small Magellanic Clouds, both of which are visible to the unaided eye. By comparison, the new stellar systems are so faint that they are difficult to “see” even in the deep DES images and can be more easily visualised using maps of the stellar density (inset). Fourteen of the dwarf galaxy candidates found in DES data are visible in this particular image. Illustration credit: Dark Energy Survey Collaboration.