If all black holes are made up of an infinitely small point with infinite density, why are there “big” black holes and “small” black holes?
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the “hole” of a black hole is merely the region in space in which the gravitational field of the collapsed star is sufficient to trap photons. The more mass the infinitesimally small core absorbs into itself the further the gravitational field stretches.
An infinitely small point of infinite density can still have some finite amount of mass.
More mass makes for a larger event horizon – a larger region of space that is inescapable due to the presence of the black hole.
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The “infinitely small/dense” refers to its volume. It’s mass, however, is finite, and different black holes can be have different masses.
It is its mass that determines its event horizon which is what we are talking about when we reference the “size” of a black hole. It is this invisible barrier beyond which nothing can escape.
Black holes do not have an infinitely small point with infinite density in the middle. It’s just the mathematical model giving up. We need quantum gravity to understand better what’s inside them. But from the outside, it doesn’t matter much, everything behave just the same as infinite density at a 0D point, so it remains a useful approximation.
Black holes are heavy enough that they wrap spacetime around them so much not even light can escape.
The size of a black hole depends on its mass, angular momentum (rotating speed), and charge. But basically, the heavier they are, the bigger the region of spacetime that is extremely wrapped. And that’s usually what we talk about when talking about their size.
The black holes themselves are just points.
The distance to that point from which not even light can escape is different from hole to hole.
The radius around the point that we usually see as the black hole is the Schwarzschild-Radius.
The mass itself is concentrate in a mathematical point. When you cross the threshold you have in theory not yet reached the actual point that is the black hole, but you can’t go back either so for practical purposes you are ‘in’ the black hole.
The amount of mass that went into the hole determines the radius.
Since any amount of mass divided by zero volume of a point will mean infinite density, any amount of mass compressed enough can be a black hole.
There is no lower limit to how much mass you need to have a black hole. You can have a black hole that is just the mass of yourself, if your body was compressed to a single point.
Such a black hole would be tiny and short lived though.
Blackholes can have different masses.
The larger the mass, the larger the schwardschild radius which is the black circle we see(or rather don’t see hehe)
That point isn’t what we “see”, we see the event horizon. The point at which not even light can escape. Any light that would have passed any closer than that gets sucked in, any light that passes around it gets bent a lot (see gravitational lensing) but still escapes.
Fun fact: due to time dilation, the lowest energy orbit you can have around a black hole is 1.5x the Schwarzchild radius (distance from the center to the event horizon) to get any closer or further away from the black hole, you would need to add energy to your orbit, so it’s actually a stable orbit.
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