Gases in outer layers heat up from below and expand outward, cooling as they expand.Hydrogen in shell surrounding shrinking core ignites and begins thermonuclear fusion to helium, which 'rains' into core, increasing its mass and density.Volume of core where thermonuclear fusion occurs shrinks and heats up., but there is no hydrogen left to fuse in the core.Supply of core hydrogen available for thermonuclear fusion to helium, carbon, nitrogen, and oxygen drops as hydrogen is converted to helium.When the core runs out of hydrogen, the star goes through a series of steps to become a red giant. The star can remain in this state burning hydrogen in the core for several billion years. In a moderate-mass star on the main sequence, energy from hydrogen fusion in the core is transmitted by radiation to outer layers, where heat drives convection currents. Stars with masses between 0.4 M ☉ and 4.0 M ☉ pass through two distinct red giant phases.

We have not observed the 'death' of red dwarfs.

In theory, since the star lacks the mass to continue to the next stage of thermonuclear synthesis and fuse helium to beryllium, it should simply fade out, but the lifetime of these stars is greater than the age of the universe. Hydrogen burns slowly throughout the entire star. Neutron Stars The Life Cycle of a Dying Star Smaller StarsĪs we have seen, very low mass stars (under 0.4 Solar Masses) called red dwarfs mix their internal gases through convection, so there is no well defined core area.Evolution of Stars on the Main Sequence.

Third dredge up final core mass