Others give off mostly one or the other. As radio telescopes and observing methods allowed for more detailed observations, this source of radio waves was constantly studied. Also, the source of the radio waves seemed to be nearly stationary, indicating that it was very massive. It gave off tremendous power. In fact, we now know that the source of Jansky's radio hiss is mostly likely a supermassive black hole at the center of the Milky Way galaxy.
Distant galaxies are also sometimes relatively strong sources of radio waves.
Material falling into the black hole is accelerated to such a high speed that it gives off intense radio radiation. Most of the matter in the Milky Way is cool hydrogen gas. Because it is cool it gives off no visible radiation. It is composed of hydrogen atoms, which in turn are composed of one proton in the nucleus, with one electron in orbit about it. Protons and electrons can be thought of as spinning like a top, with one main difference.