The forces of pressure and gravity reached a stalemate before the temperature in the star s core became hot enough to ignite nuclear reactions in the core, which is what happens in all other stars to make them hot and bright. This is the radiation left behind by the Big Bang. It's detectable today as radio-wavelength radiation, for example in the COBE map of the entire night sky. This is a term used to describe an abundant substance in the universe whose composition is unknown. Electron An electron is another of the fundamental particles, and it has a mass and a negative charge.
Electrons often orbit nuclei in atoms .
Galaxy A galaxy is a massive cluster of stars, bound together by gravity. The Milky Way is the spiral galaxy in which we live containing about 10 billion stars. Globular Cluster Globular clusters are groups of several hundred thousand stars all bound together by gravity. There are globular clusters above the disk of the Milky Way, and in the early twentieth century they were used to determine our position in the Milky Way. The Hubble Constant, or H 0 features in Hubble s Law.