The Spitzer Space Telescope's GLIMPSE catalog consists of some 30 million infrared sources along the galactic equator. This plot shows the number of sources in two strips on either side of the galaxy's center, from 10° to 22° (top) and 350° to 338° galactic longitude. The highest density of sources — about 23,000 per square degree — appears as red; lower densities map as progressively cooler colors. Benjamin's team says the clear asymmetry between the strips is caused by a bar-like structure at the Milky Way's center.
Robert Benjamin, University of Wisconsin, Whitewater