Expert: Philip Stahl - 5/27/2008

Question
Why is it impossible for the sun to turn into a black hole?

Answer
Hello,

Theoretically, any object of any mass can be transformed into a black hole IF forces can be found to squeeze the mass into a small enough volume. We call the radius for such a tiny volume, the 'Schwarzschild radius".

For the Sun, this radius turns out to be about 3 km (2 miles).

Despite that, there is no known force capable of doing this to the Sun. Large, massive stars (> 3 solar masses) become black holes by virtue of the fact they build up very heavy elements (e.g. iron, cobalt) in their cores. The cores then begin to undergo endothermic reactions (absorbing heat) and the star cannot remain stable. Its core collapses as its outer layers of gas explode out in what we call a "supernova".

Meanwhile the collapsing heavy core becomes either a neutron star or black hole. Current theoretical studies show that for a star at least THREE times the mass of the Sun, it will become a black hole.

In the case of the Sun, the heaviest element we expect it to form (by nuclear fusion) in its core is carbon (C-12). It simply lacks the original materials-elements to go beyond that, and hence become a black hole!