Will Our Sun Expand and Go Nova or Shrink into a Black Hole?

[DarkerEnergy]

Firstly, the most important factor that determines a stars evolution is it's mass. Our Sun is not even in the ball park mass to end in a supernova or a black hole. Stars spend their lives fusing hydrogen into heaver elements. Right now, The Sun is in a state of hydrostatic equilibrium. Nuclear fusion of Hydrogen into Helium causes an outward pressure via the energy produced in the reactions, which counterbalances the force of gravity. This energy via the proton-proton chain decreases the amount of matter at the Suns core slowly, causing the core to contract slightly and heat up. When the temperature rises the nuclear reactions become faster, which creates more pressure, where the Sun achieves a new equilibrium.

Eventually though, our Suns core will contract and the reactions will have to take place in a shell around the core. This will take the Sun off the main-sequence and grow into a red giant that will likely be larger than Earths orbit. The Sun will eject about 40% of it's mass and the out layers will produce what is called a planetary nebula similar to that of the Ring or Helix Nebula. All that will be left behind is but a white dwarf -- not a neutron star, which is a required first step to a black hole. Further, a neutron star must be a massive enough to overcome the electron degeneracy pressure, and further collapse to a black hole AKA the Chandrasekhar limit.






A planetary nebula



More information . . .

http://www.atnf.csiro.au/outreach//educa...thlow.html

In an AGB star, if the helium fuel in the He-burning shell runs low, the outward radiation pressure drops off. As this was previously holding out the shell of hydrogen gas this shell now contracts, heats up and ignites, converting hydrogen to helium. This helium "ash" in turn falls onto the helium shell, heating it up till it is hot enough to re-ignite in a helium-shell flash, producing a thermal pulse. Increased radiation pressure now causes the hydrogen shell to expand and cool, shutting down H-shell burning.

The interval between successive thermal pulses decreases as the AGB star ages. For solar-mass stars such pulses dramatically increase the luminosity for several decades. Over time the outer layers of the AGB star are almost totally ejected and may initially appear as a circumstellar shell. The ejected cloud contains dust grains of silicates and graphite in addition to hydrogen and elements produced via nucleosynthesis reactions within the parent star. The cloud has typical expansion velocities of tens of kilometres per second.Our Sun will shed about 40% of its mass during this phase. More massive stars lose a greater percentage of their initial mass.