Supernova Remnants (2) ...

Supernova remnants may emit at wavelengths other than visible light. For example, the collision of the expanding gases with the interstellar medium generally produces radio emission.
Radio Frequency Observation of Expansion for SN1993j
The following figure shows five sequential Very Long Baseline Array (VLBA) radio telescope observations over a one year period for Supernova 1993j. The outward motion of the expanding envelope is apparent.

Although the expansion of the debris from Supernova 1993j is approximately spherical, the radio emission appears to be much stronger on one side of the expanding remnant. It is not certain why, but presumably the shock wave is encountering a different environment in that direction than in the others. From the increase of the area of radio emission over time it is found that the debris is expanding through the interstellar medium at about 10,000 km/s. There is no indication of slowing over the time period of these images. At that speed, the advancing shock front covers a distance equivalent to that from the Earth to the Sun in only four hours. It will eventually begin to slow after sufficient interaction with the interstellar medium.