The heart of our galaxy is oddly bright. Since 2009 astronomers have suggested that too much gamma-ray light is shining from the Milky Way’s core—more than all the known sources of light can account for. From the beginning scientists have suspected that they were seeing the long-sought signal of dark matter, the invisible form of mass thought to pervade the universe. But two recent studies offer more support for an alternate explanation: The gamma rays come from a group of spinning stars called pulsars that are just slightly too dim to see with current telescopes.
Part of the confusion stems from uncertainties about the gamma-ray signal, which shows up in data from NASA’s Fermi Gamma-Ray Space Telescope. Many different groups have analyzed Fermi’s publicly available data and claimed to see an unexplained excess of light, but the details of what they find and how they interpret it vary from group to group. Now, for the first time, the Fermi telescope team has confirmed the puzzling excess in a paper submitted to The Astrophysical Journal. The study offers the best description yet of the particularities of the extra light, such as its density and spread in space and its wavelength spectrum as well as all of the contaminating factors, such as systematic errors in the telescope and other sources of gamma-ray light that may muddy the signal. The team’s analysis stokes hopes that scientists may finally be close to making sense of the signal.