I planned this article as a normal single piece. As work progressed, it became evident we should be wading into deep waters, and choose to split it. If you are troubled with the weird physics of part I, feel free to skip and go directly to part II, our galactic black hole. But make a try with part I, it helps better understand the whole thing. (And I hope it makes for interesting reading).
Brace tight, the ride may be rough.
Anatomy of a black hole.
You know matter attracts matter. This is gravity, and to a very good approximation it may be modeled with an equation that takes into account masses and distances separating objects, to compute its mutual attraction. This is what Newton did, establishing the foundations of Classic Gravity.
Problem is this equation has distance between massive objects as a divisor, which means that if it approaches 0, their mutual attraction should escalate to infinite.
You cannot divide something by 0, it falls apart, and you have what in math jargon is called a singularity.
But 0 is a mathematical abstraction, you cannot imagine two material objects, be they even smallish nuclear particles, merging to the same spatial position so as to make its mutual distance 0. Better leave things at this for now, otherwise we should be foraying into the sub nuclear quantum world with different laws altogether, laws that trick reason.
The point is, let matter aggregate densely, and the nearby gravity field (the force felt by other material object nearby because of attraction) will grow out of proportions. Pour more matter and at some point, this gravitational field grows so intense that classic Newtonian laws do not hold very well, General Relativity steps in, and it says the very fabric of space and time begin to feel the stress. This is weird, but it has been measured once and again for almost 100 years and theory agrees with observation to several decimal places.
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