Follow this Link to a NASA Web site on supernovas. It has a very nice animation and a description of what these objects are.
This is the data on Lenticular Galaxy UGC 09758 itself:
Based on the published red shift, a rough distance estimate for UGC 09758 and supernova 1999dg is: 344,000,000 light years, with the galaxy being 120,000 light years in diameter. Considering that the other stars in the image are no more than a few thousand light years at the most, it is possible to see the tremendous amount of energy released by this event.
( UGC = Uppsala General Catalog of Galaxies, 1973, Uppsala Astronomical Observatory)
Click below to
George Normandin, KAS
August 22nd, 1999