Stellar Birth

Stellar birth Key words T-Tauri star

accretion disc core HertzsprungRussell diagram main sequence mature star

nuclear fusion polar jet protostar star T-Tauri star

T-Tauri star ● If

Polar jets

temperatures become high enough for the nuclear fusion of hydrogen nuclei to occur, a protostar becomes a T-Tauri star. ● T-Tauri stars are situated just above the main sequence on a HertzsprungRussell diagram. ● Their fusion processes are restricted to a small central core. ● The star is still contracting gravitationally and some material is still falling onto its surface from an accretion disc. ● Strong winds push some material away and the star may emit polar jets of energetic radiation. ● Equilibrium has not been achieved.

Mature star ● Eventually,

the outward pressure generated by nuclear fusion balances the inward pressure of gravitation and the star achieves a stable diameter. ● Equilibrium is achieved and the star is situated on the main sequence of an H-R diagram.

Life span

Mature star and disc of leftover material

stable phase of a star’s life is usually its longest. ● This is because the nuclear fusion of hydrogen into helium is the most efficient of the nuclear burning stages. ● The length of time that a star remains in the main sequence is closely related to its mass. ● More massive stars have shorter spans of stable maturity than less massive stars.

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