This is NGC 5806, a fairly average spiral galaxy located in the constellation Virgo. In 2004, one of its stars exploded in the bright supernova you can see at the bottom of this image. And Hubble caught every crucial moment.
Since there's no way to predict when a star — especially one located 80 million light-years away — is about to explode, supernovas remain one of the more difficult cosmic phenomena to study. That's why, when precision isn't really possible, the ability to cast a very wide net is so crucial. And since Hubble has now had a chance to image countless galaxies multiple times, we're starting to build up enough exposures to create images like this, which exactly pinpoint the location of the exploding star. Here's how NASA explains it:
The exposures that are combined into this image were carried out in early 2005 in order to help pinpoint the location of the supernova, which exploded in 2004. The afterglow from this outburst of light, caused by a giant star exploding at the end of its life, can be seen as a faint yellowish dot near the bottom of the galaxy. NGC 5806 was chosen to be one of a number of galaxies in a study into supernovae because Hubble's archive already contained high resolution imagery of the galaxy, collected before the star had exploded. Since supernovae are both relatively rare, and impossible to predict with any accuracy, the existence of such before-and-after images is precious for astronomers who study these violent events...This image is produced from three exposures in visible and infrared light, observed by Hubble's Advanced Camera for Surveys. The field of view is approximately 3.3 by 1.7 arcminutes.
For more, check out the NASA site.
Image credit: ESA/NASA, acknowledgement: Andre van der Hoeven.