Gravity isn't about size, it's about mass. In fact, if everything was pulled into each other, the result would be an infinitely small, infinitely massive non-dimensional dot (try putting your head around that one

). Just think of black holes, when a supergiant star becomes unstable and goes supernova (goes boom), it's super dense (therefore super massif) core starts to collapse into itself. Since the core is so massive for its relatively small size, gravity's power is multiplied. If it is massif enough, it will literally collapse its way out of existence to form an infinately small dot (called a singularity) that is many times more massive than the Sun.
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