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The article makes it sound like a black hole with the mass of Everest wouldn't be scary, since it would only have strong attractive force within a few meters.

by shasta 11y ago

The article makes it sound like a black hole with the mass of Everest wouldn't be scary, since it would only have strong attractive force within a few meters. But wouldn't it fall to the center of the earth, absorbing anything in its way and then wouldn't the earth fall into it? Seems like its lack of strength at a few meters isn't what makes it not-scary.

XorNot 11y ago
It can only absorb matter at a rate limited by its event horizon surface area, and further limited by its ability to shear matter from outside the event horizon to fall into it. At the center of the earth, since its the gravitational locus of the planet, we wouldn't even notice it - while stuff would be falling in, the planet would still weigh the same and thus have the same surface gravity, and most of the planets material would resisit falling in by pressure against itself.
- 05 11y ago
  This is all so very wrong: - it's all liquid at very high pressures, so the pressure guarantees a steady stream of new matter to feed to the hole - even if by some miracle there was a material strong enough to hold the pressure (and temperatures at the center) of the whole earth without buckling in (spoiler: there really isn't) creating a sphere filled with vacuum with the hole at the center, it wouldn't stay centered, because gravitational forces inside the cavity in such a configuration balance out, so the smallest disturbance would make the hole move towards the edge of that empty sphere, resulting in those super-strong walls getting pulled in as well
  - abtinf 11y ago
    Earth's core is believed to be a solid ball of iron, not liquid.
  - XorNot 11y ago
    The earth's core is going to be spinning relative to the black hole. Of course a lot will fall in but any material on the outside will not make a straight line for the hole - its going to start picking up angular momentum, interacting and colliding with material which is trying to move directly toward the black hole and deflecting it. Remember anything which doesn't land on the event horizon is going to spiralling around and deflecting anything trying too. This is why blackholes glow in the X-ray in space and it would apply here too. Sure, matter will stream in at a constant rate - but there are real mechanical limits.
SeanDav 11y ago
In theory, small black holes should kill themselves almost immediately, but this aside - I find the argument that a small black hole is not dangerous because you have to get really close to it - not a valid argument (as a layman!). Assuming the black hole did not destroy itself and was big enough to attract nearby molecules and atoms, it would suck in all the molecules nearby in an endless stream, getting bigger and bigger and accelerating its growth, until it consumed the earth.
- pcl 11y ago
  I had the same thought. If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in, it'd presumably basically bore its way to the center of the Earth, aggregating matter (and thus mass) as it went. When it reached the center, I'd expect that its gravity well would pull the rest of Earth into the black hole, unless it somehow found itself in a vacuum large enough to not create a gravity well. That would presumably be a sphere the radius of the amount of core material that is equivalent to the mass of Mt Everest, plus whatever it accreted on its descent. So really, the question is whether or not a black hole that we could create would be able to make it to the floor of the lab... the article sorta touches on this: The gravitational pull of a few micrograms of matter, regardless of how it is arranged, is never dangerous; you wouldn’t get pulled inside out if you ate it. However, you wouldn’t get the chance, since any black hole that we could reasonably create would already be mid-explosion.
  - pdonis 11y ago
    > If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in Since the proposed method of creating the hole is to collide particles in an accelerator, we would expect the hole, when formed, to be moving the way particles created in an accelerator move, i.e., at close to the speed of light. So the hole would fly off into space, since it would be moving much, much faster than escape velocity. (Also, as the article notes, the hole would explode due to Hawking radiation soon after it was created.) > unless it somehow found itself in a vacuum large enough to not create a gravity well Not sure what you mean by this. The "gravity well" of the hole is the same whether it's surrounded by vacuum or matter. The only difference is what can possibly fall in.
pdonis 11y ago
> wouldn't it fall to the center of the earth, absorbing anything in its way That would depend on how it was formed and what its state of motion was. If it were moving fast enough (where "fast enough" means anything above escape velocity at the Earth's surface, 11.2 km/s--and objects created in our particle accelerators travel at close to the speed of light), it would just fly off into space. > wouldn't the earth fall into it? Not any more quickly than the Earth would fall into the existing Mount Everest. If such a hole were sitting at the center of the Earth, it would gradually accrete matter from the Earth, yes, but it wouldn't just swallow the Earth all at once.
- danharaj 11y ago
  > (where "fast enough" means anything above escape velocity at the Earth's surface, 11.2 km/s--and objects created in our particle accelerators travel at close to the speed of light) The net momentum of a collision in the LHC is 0 relative to the Earth.
  - idlewords 11y ago
    You can't create a mountain-sized black hole in a particle accelerator. At least not yet!
  - gizmo686 11y ago
    There is no guarantee that all of the momentum will end up in the black hole.
- jessriedel 11y ago
  > Not any more quickly than the Earth would fall into the existing Mount Everest. Of course it would happen more quickly. Everest is kept separate from the rest of the Earth by atomic bonds. But an Everest-mass black hole, created at rest on the Earth's surface, would fall through the ground to the center of the Earth very quickly (a few minutes of travel time), gobbling up all the matter within at least a few atoms distance of it's path. Then it would shoot past the center, sailing up toward the other side of the Earth. It would oscillate back and forth, effectively in a damped orbit about the center of the Earth, accreting more and more matter. Since the accretion rate is probably proportional to the cross-sectional area of the black hole, and the area is proportional to the mass, the black hole size would grow roughly exponentially, at least until it came to rest at the center of the Earth. At this point, it would start accreting as fast as the liquid iron or whatever can get pushed into, which I imagine becomes very fast very quickly.
lisivka 11y ago
It will not fall to the center, it will orbit around center. Nothing can stop black hole, but it will retain momentum of whatever it will sink, so it will oscillate at smaller and smaller radius, until it will replace Earth.
reportingsjr 11y ago
No, because at that mass it wouldn't be able to absorb anything faster than it would emit radiation.
bmurphy1976 11y ago
Higher energy collisions happen in the atomosphere all the time. If it were possible, it would have happened long ago. There is nothing to worry about here.
- platz 11y ago
  But that is just one little cosmic ray particle. Is it different if we're coliding a huge stream of matter? Maybe there are other variables that are important.
kevin_thibedeau 11y ago
David Brin's novel Earth posits this very situation where a black hole falls into orbit around the core slowly accumulating mass until mayhem breaks out. Also has a prescient prediction of glassholes.

by shasta 11y ago

XorNot 11y ago

It can only absorb matter at a rate limited by its event horizon surface area, and further limited by its ability to shear matter from outside the event horizon to fall into it. At the center of the earth, since its the gravitational locus of the planet, we wouldn't even notice it - while stuff would be falling in, the planet would still weigh the same and thus have the same surface gravity, and most of the planets material would resisit falling in by pressure against itself.

05 11y ago
This is all so very wrong: - it's all liquid at very high pressures, so the pressure guarantees a steady stream of new matter to feed to the hole - even if by some miracle there was a material strong enough to hold the pressure (and temperatures at the center) of the whole earth without buckling in (spoiler: there really isn't) creating a sphere filled with vacuum with the hole at the center, it wouldn't stay centered, because gravitational forces inside the cavity in such a configuration balance out, so the smallest disturbance would make the hole move towards the edge of that empty sphere, resulting in those super-strong walls getting pulled in as well
- abtinf 11y ago
  Earth's core is believed to be a solid ball of iron, not liquid.
- XorNot 11y ago
  The earth's core is going to be spinning relative to the black hole. Of course a lot will fall in but any material on the outside will not make a straight line for the hole - its going to start picking up angular momentum, interacting and colliding with material which is trying to move directly toward the black hole and deflecting it. Remember anything which doesn't land on the event horizon is going to spiralling around and deflecting anything trying too. This is why blackholes glow in the X-ray in space and it would apply here too. Sure, matter will stream in at a constant rate - but there are real mechanical limits.

SeanDav 11y ago

In theory, small black holes should kill themselves almost immediately, but this aside - I find the argument that a small black hole is not dangerous because you have to get really close to it - not a valid argument (as a layman!). Assuming the black hole did not destroy itself and was big enough to attract nearby molecules and atoms, it would suck in all the molecules nearby in an endless stream, getting bigger and bigger and accelerating its growth, until it consumed the earth.

pcl 11y ago
I had the same thought. If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in, it'd presumably basically bore its way to the center of the Earth, aggregating matter (and thus mass) as it went. When it reached the center, I'd expect that its gravity well would pull the rest of Earth into the black hole, unless it somehow found itself in a vacuum large enough to not create a gravity well. That would presumably be a sphere the radius of the amount of core material that is equivalent to the mass of Mt Everest, plus whatever it accreted on its descent. So really, the question is whether or not a black hole that we could create would be able to make it to the floor of the lab... the article sorta touches on this: The gravitational pull of a few micrograms of matter, regardless of how it is arranged, is never dangerous; you wouldn’t get pulled inside out if you ate it. However, you wouldn’t get the chance, since any black hole that we could reasonably create would already be mid-explosion.
- pdonis 11y ago
  > If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in Since the proposed method of creating the hole is to collide particles in an accelerator, we would expect the hole, when formed, to be moving the way particles created in an accelerator move, i.e., at close to the speed of light. So the hole would fly off into space, since it would be moving much, much faster than escape velocity. (Also, as the article notes, the hole would explode due to Hawking radiation soon after it was created.) > unless it somehow found itself in a vacuum large enough to not create a gravity well Not sure what you mean by this. The "gravity well" of the hole is the same whether it's surrounded by vacuum or matter. The only difference is what can possibly fall in.

pdonis 11y ago

> wouldn't it fall to the center of the earth, absorbing anything in its way That would depend on how it was formed and what its state of motion was. If it were moving fast enough (where "fast enough" means anything above escape velocity at the Earth's surface, 11.2 km/s--and objects created in our particle accelerators travel at close to the speed of light), it would just fly off into space. > wouldn't the earth fall into it? Not any more quickly than the Earth would fall into the existing Mount Everest. If such a hole were sitting at the center of the Earth, it would gradually accrete matter from the Earth, yes, but it wouldn't just swallow the Earth all at once.

danharaj 11y ago
> (where "fast enough" means anything above escape velocity at the Earth's surface, 11.2 km/s--and objects created in our particle accelerators travel at close to the speed of light) The net momentum of a collision in the LHC is 0 relative to the Earth.
- idlewords 11y ago
  You can't create a mountain-sized black hole in a particle accelerator. At least not yet!
- gizmo686 11y ago
  There is no guarantee that all of the momentum will end up in the black hole.
jessriedel 11y ago
> Not any more quickly than the Earth would fall into the existing Mount Everest. Of course it would happen more quickly. Everest is kept separate from the rest of the Earth by atomic bonds. But an Everest-mass black hole, created at rest on the Earth's surface, would fall through the ground to the center of the Earth very quickly (a few minutes of travel time), gobbling up all the matter within at least a few atoms distance of it's path. Then it would shoot past the center, sailing up toward the other side of the Earth. It would oscillate back and forth, effectively in a damped orbit about the center of the Earth, accreting more and more matter. Since the accretion rate is probably proportional to the cross-sectional area of the black hole, and the area is proportional to the mass, the black hole size would grow roughly exponentially, at least until it came to rest at the center of the Earth. At this point, it would start accreting as fast as the liquid iron or whatever can get pushed into, which I imagine becomes very fast very quickly.

lisivka 11y ago

It will not fall to the center, it will orbit around center. Nothing can stop black hole, but it will retain momentum of whatever it will sink, so it will oscillate at smaller and smaller radius, until it will replace Earth.

reportingsjr 11y ago

No, because at that mass it wouldn't be able to absorb anything faster than it would emit radiation.

bmurphy1976 11y ago

Higher energy collisions happen in the atomosphere all the time. If it were possible, it would have happened long ago. There is nothing to worry about here.

platz 11y ago
But that is just one little cosmic ray particle. Is it different if we're coliding a huge stream of matter? Maybe there are other variables that are important.

kevin_thibedeau 11y ago

David Brin's novel Earth posits this very situation where a black hole falls into orbit around the core slowly accumulating mass until mayhem breaks out. Also has a prescient prediction of glassholes.