Gravitational collapse

With the exception of a few supernova remnants which are in our galaxy, most cosmic radio sources are “radio galaxies”. Although flare stars do emit radio waves occasionally, no ordinary stars with strong, steady radio emission have been found. The typical optical power of stars is from ${10}^{30}\hspace{0.17em}\mathrm{ergs}/\sec$ (white dwarfs) to ${10}^{38}\hspace{0.17em}\mathrm{ergs}/\sec$ (super giants). For comparison, the optical power of the sun is ${\text{4×10}}^{33}\hspace{0.17em}\mathrm{ergs}/\sec .$ The typical radio power of supernova remnants is around ${10}^{36}\hspace{0.17em}\mathrm{ergs}/\sec .$ For a giant galaxy (containing approximately ${10}^{11}{\text{−10}}^{12}$ stars with a total mass of around ${10}^{11}\mathrm{\odot ,}$ where $\mathrm{\odot \hspace{0.17em}=\hspace{0.17em}}\mathrm{solar}$ ${\text{mass\hspace{0.17em}=\hspace{0.17em}2×10}}^{33}\hspace{0.17em}\mathrm{g}$ ), the optical power is around ${10}^{44}\hspace{0.17em}\mathrm{ergs}/\sec .$ Radio emission from normal galaxies is generally weaker, the power ranging from ${10}^{37}{\text{−10}}^{39}\hspace{0.17em}\mathrm{ergs}/\sec .$ For certain peculiar galaxies, the so‐called “radio galaxies,” the radio emission rate ranges from ${10}^{41}{\text{−10}}^{\text{44.5}}\hspace{0.17em}\mathrm{ergs}/\sec .$