What happens if gravity shuts down for only one second?
I expect stars would belch mightily, neutron stars and black holes would explode.
Stars are only held at their steady state size by the opposed forces of gravity and radiation, so eliminating gravity for 1 second will cause expansion, followed by collapse as gravity kicks in again.
A Neutron star's compactness gives it a surface gravity of up to 7×10^12 m/s², and expanding from 20km to ~70 billion km (or 300000km when c limit is considered) over the course of 1 second constitutes an explosion.
Black holes tend to have higher gravity values at the event horizon (same ref) so the result would be even more cataclysmic.
The expansion would happen because of the pressure. Stars are in hydrostatic equilibrium (gravity balances pressure) so if gravity falls away, the star starts to expand because of the pressure. But black holes are **NOT** in equilibrium. Where would the pressure come from?
@Dieudonné Pressure source rather depends on the nature of the stuff inside the Schwarzschild radius, doesn't it? I could be wrong, but I'd expect a force from both Electron and Neutron Degeneracy: http://minerva.union.edu/vianil/web_stuff2/Election_and_Neutron_Pressure.htm
I'm not sure but I always thought that the issue with black holes was that even the pressure from electron or neutron degeneracy could not stop gravitational collapse.
Of course, but I assume the collapse into a black hole happened long before turning of gravity. Do we know what happens to matter in a black hole?
Nope, Some say it contracts to a point, others say not. AFAIK, it's all speculation.
Are you sure that 1s would be enough for the outer layers to accelerate to a significant speed due to the pressure? I think, only the upmost layer of a NS might get to the escape velocity.
@peterh One second is a pretty short time for all that degenerate mass to turn into regular particles then expand into the vacuum. There's going to be a *lot* of collisions, but also a lot of heat released, so the ideal gas law is hardly going to apply. Perhaps only the top mile or two will make it out.