What is the Schwarzschild radius?

There’s only a certain amount you can compress some amount of mass before every molecular force is overcome, and the object collapses under the force of its own gravity. This “point of no return,” the radius past which everything collapses, is the “Schwarzchild radius,” and when the mass becomes a black hole that becomes the radius of the black hole’s event horizon. Once you pass the event horizon, it’s game over: not even light can escape!

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.