Sudden ceasing of energy generation

[blumfeld0]

I always wondered what would happen if the sun suddenly stopped doing energy generation.
i know that it would us 8.5 minutes to find as limited by the speed of light.

or perhaps 10 million years to find out as that is how long it would take a photon to travel from the core to the surface according to random walk calculations. is this a possibility?

would the sun become a black hole as gravity took over and won and pressure (caused by energy generation) stopped?
what would happen?


thanks

[mathman]

would the sun become a black hole as gravity took over and won and pressure (caused by energy generation) stopped?

It would not become a black hole - it is too small. After the sun burns out (in about 5 billion years) it will eventually collapse into a white dwarf.

[franznietzsche]

It would glow as a hot ember (it still has all that stored thermal energy after all) and slowly collapse as the thermal and radiative pressure gradients could not hold up against gravity.

[SpaceTiger]

I always wondered what would happen if the sun suddenly stopped doing energy generation.

If all fusion stopped suddenly, I suspect the sun would eventually become a degenerate object very similar to a brown dwarf, which is a star that wasn't massive enough to ignite hydrogen in its core. They're very cool and very dim, so we've only just recently been able to observe them.

In order for a white dwarf to be formed, the envelope would have to be stripped. In the absence of shell hydrogen burning around the core, I don't think this could occur.


i know that it would us 8.5 minutes to find as limited by the speed of light.

If our neutrino detectors were on, we could potentially find out in 8.5 minutes because they would stop being formed in the fusion reactions. Otherwise, however, the change probably wouldn't be noticable in a human lifetime.


or perhaps 10 million years to find out as that is how long it would take a photon to travel from the core to the surface according to random walk calculations. is this a possibility?

Significant changes would occur on the Kelvin-Helmholtz timescale, which is the approximate time it takes the sun to radiate its gravitational potential energy. This is around 30 million years for the sun.


would the sun become a black hole as gravity took over and won and pressure (caused by energy generation) stopped?

Pressure is not caused by energy generation, it is just maintained by it. As franz said, the star would gradually cool and drop in temperature, leading to a gradual drop in thermal energy. In order to compensate, the star would have to collapse. The end result would not be a black hole because the sun is not above the Chandrasekhar mass, as mathman implied.