IC 443 is an unusual occurrence of a a supernova remnant (SNR) interacting with a molecular cloud. Some 30,000 thousand years ago a great supernova detonated in the constellation Gemini leaving in its wake a shell of heated gas that gradually expanded into the interstellar medium ultimately colliding with a large molecular cloud. Much of the HII emission (red light) in the image represents ionization of the gases in the molecular cloud by the shock front of the expanding SNR. IC 443 is a type of SNR called a Thermal Composite Remnant. The main classes of SNR's are the shell remnants (Cygnus Loop), the Crab-like Remnants (M1), and composite remnants of which there are two classes, thermal and plerionic. Thermal composites have shell like characteristics in radio wavelengths and Crab-like features at X-ray wavelengths. Recently a neutron star has been identified at the center of IC 443, the fossil remnant of the dying star which set events in motion some 30,000 years ago.

Neutron stars are the collapsed cores of stars with an original mass of 15 to 30 times the mass of our sun. A neutron star packs the mass of our sun (about 1.4 solar masses) into the space of a small city (10 KM) . The incredible density (10(14) gm/cc) is responsible for the stars exotic properties. They often rotate (called pulsars when they do) at rates up to 38,000 RPM and they generate the strongest magnetic fields in the known universe (nearly 100 trillion times stronger than the earth's field).