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The good news about black holes is that even if one transited the solar system, it would be extremely unlikely to come anywhere near earth.
by trollbridge 2mo ago
The good news about black holes is that even if one transited the solar system, it would be extremely unlikely to come anywhere near earth.
- ben_w 2mo agoThe bad news is that if a black hole is not primordial, the minimum mass is high enough (2-4 M_sol) that it doesn't so much "pass through our system" as "we pass through its". I'm not 100% confident, but rough approximation suggests that a close approach of even 5 AU even at typical interstellar velocities might have an unplesant climate impact by increasing the eccentricity of our orbit.
- mynegation 2mo agoDid you mean 5 AU or 5 ly? 5 AU at 2-4 M sol intuitively seems like a complete and utter havoc.
- ben_w 2mo agoWe know what something with about 2 solar masses looks like at about 5 light years, because there is such a thing a bit closer: the Alpha Centauri system. So (and again, this is very rough approximation) I mean AU: consider the high speed of interstellar encounters so it won't be there for long, and that it takes the full pull of Sol 6 months to turn us around 180°. Also, yes, in general this would cause a lot of the Oort cloud to destabilise and a long period of bombardment of all the planets.
- kbelder 2mo agoAt 5 AU, gravitational force would be 1/25 or 4% the strength of the sun at 1 AU. If the black hole was four solar masses, it would exert a pull about 16% as strong as the sun. Probably not enough to rip us out of orbit, but enough to seriously perturb it. I think it's at least an end-of-civilization event. 5 AU is the perfect distance to really wreck Jupiter, though.
- bell-cot 2mo agoNot an astrophysicist, but I'm thinking 5 AU could quickly fry the Earth - because it takes very little in the way of solar comets, asteroids, and dust to build a temporary accretion disk around such a black hole. That disk might have a temperature of >1M degrees. Plus the dynamo effects of the disk's interactions with the solar magnetic field? Yeah. 5 ly sounds much safer.
- ben_w 2mo ago> Yeah. 5 ly sounds much safer. Well yeah. I clearly could've phrased this better though: I was aiming for "here is an example distance which *is* bad", not as it appears to have been understood "here is the distance where it is *not* bad".
- kbelder 2mo agoYeah, I'm sure you're right. I was looking purely at orbital mechanics and gravity, but I think a four-stellar-mass black hole would certainly have other harmful environmental effects that would be felt at that range.
- trollbridge 2mo agoDéstabilise orbits - definitely, but the same would be true of a star or other celestial body. But our risk of getting sucked into a black hole is really tiny. (Although personally if I had a chance to enter a black hope, I would. I’m just naturally curious.)
- 14u2c 2mo ago5AU seems incredibly close. That's inside the orbit of jupiter. How would it not destabilize the entire system?
- 98codes 2mo ago> extremely unlikely But never zero.