A Protostar is an object that forms by contraction out of the gas of a
giant molecular cloud in the
interstellar medium. The protostellar phase is an early stage in the process of star formation. For a solar-mass star it lasts about 100,000 years. It starts with a core of increased density in a molecular cloud and ends with the formation of a
T Tauri star, which then develops into a main-sequence. This is heralded by the
T Tauri wind, a type of super
solar wind that marks the change from the star accreting mass into radiating energy. Observations reveal that giant molecular clouds are approximately in a state of
virial equilibrium—on the whole, the
gravitational binding energy of the cloud is balanced by the
kinetic energy of the cloud's constituent
molecules. Any disturbance to the cloud may upset its state of equilibrium. Examples of disturbances are shock waves from
supernovae;
spiral density waves within
galaxies and the close approach or collision of another cloud. Whatever the source of the disturbance, if it is sufficiently large it may cause the force due to gravity to become greater than the force due to thermal
kinetic energy within a particular region of the cloud.
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The name given to a star in the process of formation. Detailed observations are being made of these objects by astronomers all of the time. They are found in the the dense cores of giant molecular clouds. As they are surrounded by dusty envelopes, protostars must be studied with long wavelengths of electromagnetic radiation, such as
infrared emission, because that is not attenuated as much as
visible light. Protostars are still involved in the accretion process and have no nuclear reactions taking place within them.
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