Low-mass Star Evolution
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Interstellar gas cloud.
Anomaly occurs due to some event.
Gravity pulls material in causing temperatures to rise and material to glow in infrared and radio
frequencies… protostar
When temperature reaches 7 million K, the fusion of hydrogen to helium begins… a main
sequence star is born.
While on the main sequence, the fusion in core balances the gravity trying to crush the star’s
matter… hydrostatic equilibrium
When core hydrogen is nearly spent, the core begins to shrink causing temperatures to rise.
As core shrinks, temperature continues to rise causing remaining hydrogen to burn more
quickly.
The faster burning hydrogen which remains generates more energy. This causes outer layers to
expand, cool and glow red... a red giant forms.
When hydrogen is no longer fusing helium, the core shrinks and becomes hotter.
At a core temperature of about 100 million K, helium fuses to carbon…helium flash
After the helium flash, outer layers warm and become yellow in color…yellow giant
While helium fuses in the core, a shell of hydrogen continues to burn around the core.
With most of the helium burned and shell hydrogen burning continuing, outer layers expand
greatly, cool and redden… red supergiant
As a red supergiant, the rate at which radiation streams from the star causes the outer layers to
separate… a planetary nebula
The core star shrinks and grows hotter… a white dwarf
Over time, the white dwarf will radiate all stored energy…black dwarf
High-mass star
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Interstellar gas cloud.
Anomaly occurs due to some event.
Gravity pulls material in causing temperatures to rise and material to glow in infrared and radio
frequencies… protostar
When temperature reaches 7 million K, the fusion of hydrogen to helium begins… a main
sequence star is born.
While on the main sequence, the fusion in core balances the gravity trying to crush the star’s
matter… hydrostatic equilibrium
When core hydrogen is nearly spent, the core begins to shrink causing temperatures to rise.
As core shrinks, temperature continues to rise causing remaining hydrogen to burn more
quickly.
A high-mass star on the main sequence is hotter, bluer and more luminous than our star.
The faster burning hydrogen generates more energy. This causes outer layers of the high-mass
star to expand, move through a pulsating yellow giant phase and onto becoming a red giant.
As each fuel-hydrogen, helium, carbon- is exhausted, the star’s core contracts and heats by
compression.
Hydrogen becomes helium, helium carbon, carbon oxygen, oxygen neon, neon silicon and finally
silicon iron
The formation of an iron core signals the end of a massive star’s life since iron cannot burn.
Nuclear fusion stops with iron causing a star’s core to shrink and heat.
The shrinkage of the iron core forces protons and electrons to merge to form neutrons.
The star’s core pressure suddenly drops and the star’s interior begins to collapse.
The star’s outer layers with nothing to support them, plummet inward.
The plunging outer layers of the star strike the neutron core heating the infalling matter,
pressure surges and results in a supernova.
The supernova remnant core either survives as a neutron star or continues on the path to
becoming a black hole.