Re:What if Planet 9 is a Primordial Black Hole? (2019)
by TrainedMonkey on Friday August 13, 2021 @02:01PM
(#28172210)
As usual the answer is - it depends, but we could estimate forces in question. Assuming my math is correct, at 67 kilometers getting 1 meter closer will results in gravitational pull difference of 137kg. At 40 kilometers, this number increases to ~623kg. I am assuming bad things will happen somewhere between those two ranges.
F = G * (m1 * m2) / r^2 . G = 6.674 / 10^11 (m^3 / (kg * s^2)) | m1 = 5 * 5.972 * 10^24 kg | m2 = 100 kg
Only r in the equation above is not a constant, so we can compute F(r) - F(r+1) to get a difference in force that being 1 meter closer to the black hole would make at a distance r. Basically, this is the difference between how hard your toes would be pulled down vs your heard if you curl into a ball.
Distance Force Force + 1 Diff in kg
1 1.99286E+17 4.98214E+16 1.49464E+16
1000 1.99286E+11 1.98888E+11 39797421.92
10000 1992856400 1992457888 39851.15023
20000 498214100 498164282.3 4981.767364
30000 221428488.9 221413727.7 1476.11612
40000 124553525 124547297.6 622.744272
50000 79714256 79711067.53 318.8474585
60000 55357122.22 55355277.03 184.5191277
70000 40670538.78 40669376.79 116.1990494
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by tinco on Friday August 13, 2021 @07:21PM
(#28176064)
Very cool, thanks! It's closer than I thought, yet just too far to see it unless it's causing things to happen around it. I suppose if it would crash (slowly :p) into the earth and you were at 67 kilometers you'd see some crazy things.
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by TeMPOraL on Friday August 13, 2021 @07:42PM
(#28176227)
Worth remember for comparison that the Kármán line is at 100 kilometers. ISS orbits at ~400 kilometers. So, if such a hole were to appear on the surface of the planet, even the crew of the ISS would have a very bad day.
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by vladTheInhaler on Saturday August 14, 2021 @03:09AM
(#28178709)
Well the ISS orbits at R_earth + 400 km. So it wouldn't be nearly as bad as that number makes it sound.
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by spfzero on Friday August 13, 2021 @06:58PM
(#28175865)
Before you got very far into this it would be really hard to stay curled up in a ball.
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by 7373737373 on Friday August 13, 2021 @08:46PM
(#28176683)
Does anyone know how fast one would fall in from a 100km initial distance?
This answer: https://physics.stackexchange.com/a/332510/236187 seems to suggest that it takes mere milliseconds once one is within three times the Schwarzschild radius of the black hole. And that dozens of radii outward, one already moves at a significant fraction of the speed of light.
Re:What if Planet 9 is a Primordial Black Hole? (2019)
by ebcoajssjofb on Friday August 13, 2021 @12:57PM
(#28171477)
I believe that the Roche limit would be roughly the same as it is on earth. However, the gravity constant would be the same. So for something as massive as a person, you should not experience any destructive forces until you reached extremely close to the object. Probably measured in a handful of miles or less.
edit: ok maybe we'd need it to be between us and the sun for that to work, the lensing would be that of other stars I guess. I suppose the important question is, since it's relatively close to us, would it deform space hard enough for the gravitational lensing to be noticeable at such close proximity.
edit2: more train of thought, just because it's fun, I suppose since it's so small and the gravity relatively weak (i.e. not as strong as some huge stars or galaxies) any halo or distortion would not extend more than a couple meter, which wouldn't be noticeable from our distance, right?