he dictionary defines a protostar as a hypothetical cloud of dust and atoms in space believed to develop into a star. Astronomers are fairly certain of their existence. A protostar is formed about a million years after a gas clump from an interstellar gas cloud has started to rotate and form a disk. The protostar is simply the core of the disk that formed from the clump of gas that was compressed inside the gas cloud.

he protostar is hotter than the gas it condensed from yet is still cooler than ordinary stars. The low temperature makes the protostar visible only to infrared and radio wavelengths. This low temperature doesn't last long as the protostar grows hotter because of the gravitational energy released by infalling matter.

hen the protostar reaches about seven million degrees Kelvin, nuclear reactions begin in its core, and eventually enough pressure is built up to prevent any further collapse. Surrounding material continues to fall on the young star for millions of years. In fact, the star gains more energy from infalling material than the nuclear reactions in its core.

hese stages take a few million years in stars like the Sun and even less time in more Massive Stars. In all stars the infall creates violent changes in brightness as well as an unexplained outflow of gas.