A、In the first stage in the life of a star, the hot gas is drawn by the force of gravity into a burning sphere.
B、Scientists speculate that stars were first formed from the gases floating in the universe at the beginning of time.
C、A black hole has thus been formed.
D、But gravity soon takes over again, and the exploded star falls back in on itself with such force that all the matter in the star is compacted into a mass no larger than a few miles in diameter.
E、At this point, no heavenly body can be seen in that area of the sky, as the tremendous pull of gravity lets nothing escape, not even light.
F、A black hole in space, from all indications, is the result of the death of a star.
G、In the middle stage—our own sun being a middle-aged star—the burning continues at a regular rate, giving off enormous amounts of heat and light.
H、As it grows old, however, the star eventually explodes to become what is called a nova,a superstar.
