Does Star Evolution Always Lead to Expansion?

[Maria76]

Hi,

When the core of a star shrinks during its evolution, does it always lead to the expansion of the star? If not, why? What cases would cause it to expand?

Thanks in advance,
Maria

 

[Arch2008]

No, sometimes gravity from the mass of the star overcomes the energy from core fusion to shrink the star into a white dwarf about the volume of the Earth (which is held up by electron degeneracy) or a neutron star about the diameter of a city (which is held up by neutron degeneracy) or it collapses to a black hole.

http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html
http://imagine.gsfc.nasa.gov/docs/science/know_l1/neutron_stars.html
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

One case that causes it to expand is when the core fuses helium into carbon.

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971016.html

Arthur Eddington used the Hertzsprung-Russell diagram to demonstrate stellar physics.
http://en.wikipedia.org/wiki/Hertzsprung-Russell_diagram