Black hole with radius of 50km (escape velocity of speed of light at radius X is definition of Schwarzshild radius for nonrotating black hole) would have mass of 17 suns.
We are talking about small primordial black holes, in the vicinity of 10-50 times mass of Earth.
At 10 Earths, the radius is 8cm (!!!) and at 50 Earths it is still measly 44cm.
You can calculate the orbital velocity of an object from your distance from the object. v=sqrt(Gm/r) where v is the velocity, G is the gravitational constant, m is the mass of the black hole, and r is the distance from the black hole. Any slower and it’ll fall in; faster and it’ll drift away.
For an object 10x the size of the earth, a satellite would need to travel at 282300m/s to orbit the object at 50km. He’s off by a factor of 1000, due to units change from m to km. This is about a thousandth of the speed of light, but about 4x the speed of the fastest manmade object.
If you weren’t at orbital velocity and were stopped instead, you’d be pulled towards the black hole at 162600g of acceleration.
10mass of the earth is a lot of mass. You get pulled towards the earth at the rate of 1g when you’re (earth’s radius) distance away from the center of earth, you’re dealing with an insane amount of force when you’re only 50km away.
Wasn't Recurecur talking about a 1 mass-of-earth BH, with a dyson-sphere-like structure 50 km away from it, rather than a 50km black hole? I don't understand the physics here myself, just checking if you haven't missed his point.
We are talking about small primordial black holes, in the vicinity of 10-50 times mass of Earth.
At 10 Earths, the radius is 8cm (!!!) and at 50 Earths it is still measly 44cm.