Multiwavelength Milky Way: Across the Spectrum

II. What are the typical objects studied at different wavelengths?
Radio Active galaxies (such as radio galaxies and quasars), some stars (particularly binary stars), supernovae, pulsars, and clouds of cold molecular gas are typical emitters of radio waves. The Sun and the planet Jupiter also produce radio signals. Synchrotron emission and thermal emission are two physical mechanisms behind radio emission.

Infrared If an object has a temperature above zero, it emits in the infrared. The longer wavelengths of infrared light can pass un-scattered through dust that blocks visible light. In the infrared, we see stars, including smaller and cooler stars which are hard to see in visible light. Stars do not shine as you move into the far-infrared (towards the radio region). The far-infrared emission comes from protostars, and the dust clouds that were transparent in the near-infrared. The dust is very cold, but still warm enough for thermal radiation.

Visible (optical) In the visible region of the electromagnetic spectrum, we see large and bright stars in our galaxy, nebulae, supernova remnants, planets, and galaxies.

Ultraviolet (optical) In the ultraviolet, we see hot stars in our galaxy, and quasars in other galaxies. Gas that has been heated to a million degrees can be seen in the ultraviolet.

X-rays An object shines in x-rays if it is very hot (like millions of degrees hot!). High temperatures can be reached in the presence of magnetic fields or extreme gravity, or events such as supernovae can heat surrounding material. Hot interstellar gas, neutron stars, and supernova remnants are some objects that are studied in x-rays.

Gamma rays Gamma rays are produced by changes in atomic nuclei. They are also products of collisions between cosmic rays and interstellar matter. The objects and phenomena most often studied in gamma rays include neutron stars, quasars, black holes, and gamma ray bursts.