Why is Cassiopeia A such a strong radio source?
This nebula is the product of a supernova explosion; in this section, the blast wave has encountered an area of dense interstellar gas, creating turbulence in the wave and causing it to glow. The picture is a composite of three images taken by the Hubble Space Telescope.
Cassiopeia A is the strongest source of radio emission in the sky beyond our solar system because it is a young supernova remnant that radiates energy primarily through synchrotron radiation.31
This intense radio emission is produced by charged particles, specifically electrons, spiraling within a magnetic field at velocities approaching the speed of light. While the explosion that created Cassiopeia A occurred around 1680, it was largely obscured from optical observation by interstellar dust, leaving it relatively inconspicuous at visible wavelengths. However, because radio waves can penetrate this obscuring dust, the remnant remains spectacularly visible and powerful to radio telescopes.123