• When infrared light begins to shine from these cloudlets due to gravitational energy release, the cloudlets are called protostars.

    • As the protostar continues to collapse, temperature and pressure continues to increase until they get high enough for nuclear reactions to start Right Arrow A star is born!

    • The star now is burning H into He in its core and is a main sequence star on the H-R Diagram. It will remain on the main sequence for 90% of its life!

  • Life on the Main Sequence
    • High mass stars will remain on the main sequence for a relatively short time (2 x 107 years for a 10 Msun star) and low mass stars for a much longer time (1010 years for a 1 Msun star).

    • H continuously gets converted to He in the core, the rest of the star retains the chemical abundance that it had at birth (90% H, 9% He, with traces of heavier elements).
    • The Sun is currently halfway through its main sequence lifetime of 10 billion years.

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