Download The Life Cycle of a Star

The Life Cycle of a Star
Main Sequence Stars
Once fusion begins, hydrogen is continually consumed and helium accumulates in the core of the star. Core temperature and pressure increase and the result is a stable state which we refer to as the equilibrium. The time a star stays in this state depends on its mass.
Low Mass Stars
Low­mass stars (red dwarfs) consume hydrogen at a very slow rate (~ 100 billion years). During this time, they lose significant mass, and eventually evaporate. The result is a very faint white dwarf.
Intermediate Mass Stars
Intermediate­mass stars consume hydrogen at a faster rate (~ 10 billion years). As the core contracts from its own gravity, the outer layers expand.
When the core reaches 100 000 000 oC, the helium fuses into carbon.
Because of the expansion, the outer layers are much cooler than when the star was in the main sequence. It therefore appears as a red giant. Our Sun is considered an intermediate mass star and will evolve to this phase in about 5 billion years, its diameter expanding beyond what is now the size of the orbit of Mars. Stellar winds will peel away gases of the red giant and over time, its remnant will cool slowly and lose its brightness. It then becomes a white dwarf. The Sun
red giant
white dwarf
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High Mass Stars
High­mass stars consume hydrogen extremely fast (~ 7 million years). Their core gets so hot the helium fuses into heavier elements. This releases a vast amount of energy so the star swells into a “supergiant”.
In high mass stars, the extremely high temperature of the core of the star allows fusion to create any of the elements that come before iron on the periodic table
When a high mass star dies, its iron core __________________ and the outer
portion of the star _________________ causing a supernova which is very bright
Depending on how large the high mass star is, following supernova it can either become a ____________________
or a ________________________
Summary Chart
Size Name/Example Lifetime supernova
End of Life Low­mass star Red Dwarf 100 billion years Burns out into a white dwarf Intermediate Mass Star Ex.Our Sun 10 billion years Cools and expands into a Red Giant 7 million years Goes Supernova and becomes either a neutron star of a blackhole Massive Star
Super­giant As the size of a star increases the length of its lifetime _______________
What size star can become a blackhole? ___________________
What type of star is our Sun? ___________________ 2