| ▲ | ben_w 2 hours ago |
| The 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. |
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| ▲ | trollbridge 2 hours ago | parent | next [-] |
| Déstabilise 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.) |
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| ▲ | 14u2c 2 hours ago | parent | prev | next [-] |
| 5AU seems incredibly close. That's inside the orbit of jupiter. How would it not destabilize the entire system? |
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| ▲ | mynegation 2 hours ago | parent | prev [-] |
| Did you mean 5 AU or 5 ly? 5 AU at 2-4 M sol intuitively seems like a complete and utter havoc. |
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| ▲ | ben_w 2 hours ago | parent | next [-] | | We 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 2 hours ago | parent | prev [-] | | At 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 2 hours ago | parent [-] | | Not 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 an hour ago | parent [-] | | > 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". | | |
| ▲ | bell-cot 32 minutes ago | parent [-] | | I mostly noticed your "might have an unplesant climate impact by increasing the eccentricity of our orbit", and thought that'd be the least of Earth's worries. Black hole gravity is ruthless about turning nearby mass into deadly fireworks. | | |
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