Kanishka NaikSNRs are classified by their emission structure. Shell-type remnants show limb-brightened radio emission. Crab-like remnants are pulsar wind nebulae. Composite remnants combine both a shell and a central pulsar wind nebula.
An SNR's shock front heats interstellar gas to over one million kelvins, producing X-ray emission. NASA's Chandra maps this hot plasma to measure remnant temperatures, ages, and elemental compositions, including asymmetric distributions of iron, silicon, and sulfur.
SNR expansion rates are measured by comparing multi-epoch images separated by years. Dividing the angular size change by elapsed time yields the expansion rate, which allows astronomers to estimate when the original supernova occurred—often corroborating historical records of guest stars.