- active galactic center
- A mysterious region of extremely high energy found at the center of many galaxies, often obscured by dust and gas.
- muon
- A subatomic particle, similar to the electron, but with a different mass, and a lifetime of two millionths of a second.
- neutron star
- An end stage of stellar evolution, occurs after a supernova. Composed entirely of neutrons, the star has a density of billions of tons per cubic centimeter.
- photomultiplier tube
- A device which works like a backwards light bulb. Instead of converting electricity into light, it converts light into an electric signal, then amplifies it enough to be useful.
