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The "death of a star," meaning what happens to a star after its life on the main sequence, depends on its mass.
High mass main-sequence stars (with main-sequence mass greater than 10 solar masses or so) undergoe the following phases: red giant, then Type II supernova, then neutron star or black hole, depending on the mass of the collapsing core.
A supermassive red giant will eventually explode as a Type II supernova. This is the largest explosion in the universe (except for the Big Bang, of course) and the energy is so great that during the process, all element of the periodic table with atomic numbers greater than iron are produced.
While the outer layers of the red giant fly outward during the supernova, the core of the star gravitationally collapses. If the core has a mass less than 2 to 3 solar masses, the core becomes a neutron star. Only tightly packed neutrons can balance the large gravitational force to keep the neutron star in equilibrium.
A neutron star has mass of about 2 solar masses packed into a diameter of about 20 km, or about 12 miles. That's about the driving distance from High Point University to the PTI airport in Greensboro. Imagine two times the mass of our Sun packed into a sphere of that diameter! That's the most dense object in our universe, except for a black hole
If the collapsing mass of the core of an exploding red giant (i.e. Type II supernova) is greater than two to three solar masses, then the very large gravitational force of the collapsing mass is too large to be resisted by packed neutrons, or any other matter. There is nothing to resist the gravitational collapse, and as a result, the mass collapses to a singularity--zero volume.
It seems absurd, physically implausible that mass greater than 2 or 3 solar masses (even hundreds of thousands of solar masses) can be packed into zero volume. Density is mass divided by volume; thus mass divided by zero gives infinity. A black hole has infinite density.
Though difficult to comprehend, it is actually predicted by theoretical physics.
To test your understanding of stellar evolution of low mass stars and high mass stars, print the following flowchart and fill in the blank ovals using the following terms:
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