These X-ray images of the central region of the Andromeda Galaxy were taken in June (above) and December 2000 (below) with XMM-Newton's EPIC-MOS camera. The newly discovered X-ray Nova XMMU J004234.1+411808 and a transient supersoft X-ray pulsating source are marked by red and yellow circles respectively (courtesy of S. Trudolyubov).
The differences between the two images can be clearly seen by blinking between the two images. You can see this at the following location:
blinking between the two images. You can see this at the following location: http://sci2.esa.int/xmmnewton/images/Andromeda_June_Dec_2000/xmm.htm