Andromeda halo (illustration) (IMAGE) NASA/Goddard Space Flight Center Caption This illustration shows the location of the 43 quasars scientists used to probe Andromeda's gaseous halo. These quasars--the very distant, brilliant cores of active galaxies powered by black holes--are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars' light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo's material. Credit NASA, ESA, and E. Wheatley (STScI) Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.