to what density must the matter of a 20M☉ star be compressed in order for the star to dissapear within its event horizon?

How much energy would be released if a star with a mass of 25 Msun and a radius of 10 Rsun detonates as a supernova explosion in 1 second? (Hint: think about the definition of binding energy). Express your answer in terms of solar luminosities.

If the sun expanded to a radius 200 times it's present radius, what would the average density be (in g/cm^3?)

A supernova’s energy is often compared to the total energy output of the Sun over its lifetime. Using the Sun’s current luminosity, calculate the total solar energy output, assuming a 1010 year main-sequence lifetime. Using Einstein’s formula E=mc2 calculate the equivalent amount of mass, expressed in Earth masses. [Hint: The total energy output of the Sun over its lifetime is given by its current luminosity times the number of seconds in a year times its ten billion-year lifetime; ; mass of earth = 6×1024kg; c = 3×108m/s. Your answer should be 200-300 Earth masses.]