Here's why:

* Long Wavelengths: Radio waves have the longest wavelengths in the electromagnetic spectrum, which allows them to penetrate interstellar dust and gas that obscures visible light. This means radio telescopes can see objects and processes that are invisible to optical telescopes.

* Cosmic Radio Sources: Many astronomical objects emit radio waves, including stars, galaxies, pulsars, supernova remnants, and even the cosmic microwave background radiation.

* Unique Information: Radio waves provide unique information about the universe. They reveal the temperature, composition, and motion of celestial objects.

While some radio telescopes can also detect other wavelengths like infrared, the vast majority are designed to observe the radio wave portion of the electromagnetic spectrum.