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by est31
1507 days ago
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The formula for the gravitational pull is the same for black holes and regular objects. That means, you can orbit a black hole of the mass of the earth from 10 thousand km away just as easily as you can orbit earth itself 10 thousand km away from earth's center. Low earth orbit is in fact below that at only 7 thousand km. The difference really starts to matter as you get inside a planet's radius. As you wander closer to earths center, the gravitational pull continues trending downward and gets replaced by pressure, aka having to support increasingly large portions of the planet. Eventually you'll be killed by that pressure, as no material is known to survive the pressure. Humanity hasn't made it further than a dozen km into the rocky part of earth's surface, the fraction of a fraction of earth's radius. Mostly, earth's insides are inaccessible to us. For black holes, this is different. The gravitational pull just keeps getting stronger and stronger the closer you get to the event horizon. Eventually you'll be killed by tidal forces. But at the height of a circular orbit at the same height as earth's surface, those are the same as on earth, aka not really something to worry about for humans. To give it in explicit numbers, a 2 meter tall object of 80 kg mass standing on the surface of earth gets about 0.5 milinewtons of tidal forces (while having to deal with 785 newtons due to normal gravity): https://www.wolframalpha.com/input?i=80kg+*+G+*+mass+of+eart... Thus, you can get much closer to a black hole than you can get to earth's center. |
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