All electromagnetic radiation, whether it is the dangerous gamma rays and X-rays, or visible light, or whether it's radio waves, etc., all propagate at the same speed; namely, the speed of light.
The range of these wavelengths (the range, not the radiation itself) is called the electromagnetic spectrum (see graphic below).
Visible light; i.e., the EM radiation our eyeballs can actually see, is only a very tiny slice out of the full range of electromagnetic wavelengths. When you look up at the night sky, it's like looking at the universe through a skinny straw. You see the visible light, but can't see all the other stuff. You're missing 99% of it.
That's why astronomers now have the gamma-ray telescope (the Fermi Gamma-ray space telescope), X-ray telescopes (a bunch of them), ultraviolet telescopes, etc., in space, so they can observe the universe in its full splendor.
