| SN 1181, RX J18565‑3754, G2920+018, SN 1572, Cassiopeia A|3C 58 Wikipedia
3C58 or 3C 58 is a pulsar and supernova remnant within the Milky Way that is possibly associated with the supernova SN 1181. There are, however, signs that indicate that it could be several thousand years old, and thus not associated with that supernova.
3C58 is notable for its very high rate of cooling which is unexplained by standard theories of neutron star formation. It is hypothesized that extreme conditions in the star's interior cause a high neutrino flux, which carries away the energy and the star cools.
It is located in the direction of Cassiopeia and is estimated to be 10,000 light-years away.
3C58 has been proposed as a possible quark star.