So, a black hole is very dense that you can get really close to its center of mass that it has a strong pull, well, if i have the mass of a black hole that has a really small event horizon, why doesnt my center of mass create an explosion from hawking radiation, or suck myself
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2$\begingroup$ Mass does not make a black hole. Mass density (mass per volume) does. You are MUCH less dense than any black hole, also in your centre, even when you just ate a big meal. $\endgroup$– planetmakerCommented May 21, 2021 at 17:44
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2$\begingroup$ As a human, you would need to compact yourself to smaller than the classical radius of an electron before you'd be dense enough to fit inside your own event horizon. $\endgroup$– notovnyCommented May 21, 2021 at 20:50
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2$\begingroup$ Woops, made a mistake there. The classical electron radius is ten orders of magnitude larger than the size of a human-mass event horizon (About $10^{-25}$ m) $\endgroup$– notovnyCommented May 21, 2021 at 20:58
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2$\begingroup$ FWIW, a 135.725 million solar mass black hole (which has a Schwarzschild radius of 2.68 au) has an effective density equal to that of water, 1000 kg/m³ (i.e., roughly the same density as a human). $\endgroup$– PM 2RingCommented May 21, 2021 at 21:48
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2$\begingroup$ "why doesnt my center of mass create an explosion from hawking radiation, or suck myself?" Why would it? $\endgroup$– Daddy KropotkinCommented May 21, 2021 at 22:33
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4 Answers
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Because you are somewhat larger than your Schwarzchild radius.
In order to turn into a black hole and start experiencing exciting things like Hawking radiation, you'd need to be compressed down into a ball about $10^{-25}$ meters in diameter, about one ten-billionth the size of a single proton. At that size, you'd have a hard time sucking anything in: your gravity falls off quickly with distance, and even most subatomic particles will just bend their paths slightly as they pass you by.
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If you have a spherical ball of matter, then outside that ball of matter, the gravitational field is the same as if all them mass were concentrated at a point (as a black hole)
But inside the ball of matter, some of the mass of the ball is behind you and acts in the opposite direction. This means that the gravitational field is at a maximum on the surface of the ball, and decreases to zero as you move towards the centre of mass.
You aren't a spherical ball, but the same principle applies: The gravitational field you produce becomes smaller inside you. To get a black hole you need to have mass inside the Schwarzschild radius not outside it. A black hole exists because you can get very close to the centre of mass, without having to go inside the object.
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I will try to generalize your question to 'why does any object not become a black hole?'. It is indeed true that the center of mass of an object pulls the mass around it, so why does it not collapse?
We need to see, what force is balancing the force of gravity. If you press an object (let's say: Iron), as hard as you can, why does it not get destroyed completely? There is certainly a force that is acting against or repelling your applied push force. This force is called the electromagnetic force. It is this force by which electron repels another electron and attract a proton. What is happening when you press on an Iron is that the electrons in Iron are repelling the electrons in your hand. Since, this is a very strong force and stronger than the force you can apply with your bare hand, you are unable to destroy iron. This is the reason why atoms do not collapse under their own gravity.
In case, the gravitational pull becomes very strong, the electron repulsive force is unable to counter the gravity and the object starts to collapse. As a result, the electrons start getting nearer to each other. But this has its limit. When the object becomes too dense, the electrons become degenerate (meaning that they cannot get any closer). Now, the electron degeneracy pressure takes over to counter the gravity. This pressure is much stronger than earlier and is found in planets/white dwarfs. This is the reason white dwarfs or planets and moons do not collapse under their own gravity.
But, if even electron degeneracy pressure is unable to hold gravity, the electrons all collapse into the nucleus of the star and this results $electron+proton \rightarrow neutron$. Now, the neutron degeneracy pressure takes over and this is what is seen in Neutron stars.
Finally, if none of this helps and the gravity is just way too strong, which happens if the radius of the object is smaller than the Schwarzchild radius, even these neutrons collapse and we get a black hole.
So, now, getting back to your question, why do you not collapse under your own gravity, the answer is simply because you are not massive enough that your gravitational pull can overcome the electromagnetic (or electron repulsive) force.
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$\begingroup$ +1 I think you answered the question the OP was trying to ask. $\endgroup$ Commented May 29, 2021 at 2:13
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A black hole does not necessarily suck in everything around it. Something that is outside $r = 2GM/ c^2$ radial distance (Schwarzschild radius) from the black hole, behaves in a similar way as if the black hole were a normal gravitating object.
Here is a Schwarzschild radius calculator online
For a mass equal to that of the earth, the Schwarzschild radius is about 9 mm. The earth would become a black hole if its entire mass is compressed to less than this radius. Even in such a scenario, outside this radius, objects would anyway behave in such a way as if there was a normal gravitational source.
For a 150 lb human being, the Schwarzschild radius would be practically zero.
Think about an alien object very very close to your centre of mass (inside your theoretical event horizon). Even though the net gravity of your body might be pulling the object towards your centre of mass, the effect would be very weak because there is mass of your body everywhere around the object, pulling it around in all directions. Therefore, your centre of mass does not behave like a micro blackhole (even in classical Physics reasoning).
