(via APOD: 2012 October 9 - Simeis 147: Supernova Remnant)
Simeis 147: Supernova Remnant
Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)
The remnant of a supernova event, cataloged as Simeis 147 or Sharpless2-240, this ball of glowing debris is a full three degrees across in the sky, between Taurus and Auriga. The red glow is narrow-band hydrogen-alpha data, showing the gas that has been abruptly heated by the shockwave of the supernova, ionizing it. As it re-cools and collects electrons again, it glows red.
The explosion left behind a spinning neutron star, a pulsar, at the core.