Intresting blackhole fact I jsut found.
- Thread starter K.I.L.E.R
- Start date
Yes
Anything that has a mass great enough to create an event horizon has enough gravitational force to pull you into it. Size doesn't matter in gravity, only mass and distance.
DemoCoder said:
Unless there are people stepping on it all the time, adding to it's mass and allowing it to grow
A black hole that small will be less than 10 microgram, and because it's so small it is quite hard to hit one even for an atom. So I think it wouldn't be very dangerous. However, such a small black hole is likely to explode in very short time, and the energy would be quite large so it's still very dangerous.
Crusher said:
It was my understanding that according to Roy Kerr's solution, a rotating 'Black Hole' (eg. that unlike Schwarzshild's which were static and not representative of those in nature) doesn't collapse to a point, but rather a ring, with it's own set of unique properties. For example, due to the curvature of space-time, any matter approaching the ring from it's spatial side will hit the ring and be destroyed as the gravitational 'force' applied would be infinate. Where as if you'd enter perpendicular and 'threw' the ring's axis of rotation, the effects duie to the curvature of space-times topography would be massive, but finite.
So, in a physical sence you'd be toaat - but in a theoretical sence there is no infinate value preventing travel talong the axis of rotation in a Kerr Blackhole.
K.I.L.E.R said:
Better known as Planck's Length... good thing to memorize and impress your friends
1.6*10^-35 m.Also, I allways assumed that QTheory alone wouldn't be powerfull enough to solve the Quantum effects (Quantum Corrections, et al) happening and we'd need 10d String Theory+ to solve it. But, I'm probobly hopelessly out of date
Vince
Getting infinites out of physics equations/theories is more a sign of the system being fed invalid parameters or that the system can't describe the phenomenon in question.
Rule of thumb: If you get something infinite out of a physics equation, you're doing something wrong.
Getting infinites out of physics equations/theories is more a sign of the system being fed invalid parameters or that the system can't describe the phenomenon in question.
Crusher said:
That's a common misconception about black holes. Not helped by the way they are reported in the media, or dealt with in science fiction.
A black hole with the mass of a tennis ball has the same gravitational field as a tennis ball the size of a tennis ball (to first order). When was the last time you were sucked into a tennis ball? The fact that it's a black hole does not make it the super-mega-death killer that the screaming media would like to have you think.
There are two "magic" things about black holes: firstly density (which is what makes them black holes), and secondly the BHs we can detected (directly or indirectly) tend be exceeedingly massive (from a Solar mass to 100s of millions of Solar masses). A 10^8 Solar mass black hole exterts a very powerful gravitational influence on its surroundings, but then so would anything with a mass of 10^8 Solar masses. What makes a black hole different is that you can pack that mass into a very small volume. The fact that it's a black hole doesn't make it more dangerous per se, you need to take into account the mass too.
why is everyone stepping on black holes (regardless of size), are we so bored with life that we need a challenge.
later,
later,
K.I.L.E.R said:nutball, so I can step on a black hole the size of a tennis ball without it killing me?
No, a black hole of the size of a tennis ball should be very heavy (likely heavier than the earth). That will definitely kill anything in proximity.
However, a black hole of the mass of a tennis ball should be very small (perhaps smaller than an electron). It would be very hard to step on one.
I don't know why would one want to step on a black hole, though. However, it would be interesting to see what happens when one get into a very huge black hole (radius of several thousand light years).
Right, except that in order for it to be considered a black hole, it needs to have a high enough mass to invoke a gravitational field that is so powerful that light cannot escape it, which to me implies a mass significantly greater than a tennis ball, as I don't think the mass of a tennis ball can be made dense enough to do that. But if it could, I don't think you could play tennis with it. I think instead, it would enter a chain reaction where it absorbed all the atoms from the atmosphere, you (when you step on it), and eventually the entire mass of the earth (it would probably stop there... might get the moon too).
If it's strong enough to capture light, it's strong enough to keep pulling atoms from everything it comes in contact with, and I don't think it would 'evaporate' unless it started in the middle of nothing to begin with, and had no matter nearby to absorb, in which case you wouldn't have to worry about stepping on it. But we'll ignore that situation, just as we're ignoring the fact that we don't posses the incredible ammount of energy required to compress the mass of a tennis ball into an imperceptibly small, incredibly dense object that light cannot escape from.
If it's strong enough to capture light, it's strong enough to keep pulling atoms from everything it comes in contact with, and I don't think it would 'evaporate' unless it started in the middle of nothing to begin with, and had no matter nearby to absorb, in which case you wouldn't have to worry about stepping on it. But we'll ignore that situation, just as we're ignoring the fact that we don't posses the incredible ammount of energy required to compress the mass of a tennis ball into an imperceptibly small, incredibly dense object that light cannot escape from.
Crusher said:
Escape velocity is given by the equation v = sqrt(2 * G * M / r), where G is the gravitational constant, M is the mass of the body in question, and r is its radius. For any non-zero M there is a radius r for which v > c (c = speed of light). Ergo in principle any mass M can have an event horizon.
The key to creating your black hole is squashing the matter down to a small enough r. Black holes form in nature because you run out of forces to support them against their own weight. White dwarf stars are supported against their own weight by electron degeneracy pressure. At a given mass (the Chandrasekar limit) this gives way and the star collapses to form a neutron star, which is supported by neutron degeneracy pressure. Increasing the mass still further you run out of forces, and the star collapses to form a black hole.
Clearly a tennis ball can't collapse under its own weight naturally, so such things are unlikely to form naturally. However this doesn't mean that a black hole with the mass of a tennis ball isn't theoretically possible.
There you go with your science fiction again! A black hole the mass of a tennis ball would orbit the Earth like a tennis ball with the mass of a tennis ball. The Earth and the atmosphere would probably notice a tennis ball mass black hole less than it would a tennis ball mass tennis ball.
A tennis ball mass black hole would be incredibly small, and it's cross-section of interaction would be similarly tiny. It would be more likely to pass completely unnoticed between the atoms which constitute the Earth and its atmosphere.
nutball said:
Could be wrong, but I'm pretty sure that's not true, since for most objects the value of r would be less than the diameter of the object, and I don't think that equation holds true inside the boundry of the massive object.
nutball said:
I still think that would only be the case if it weren't a "true" black hole... that is, if the value of r from the equation above is noticably larger than the radius of the object itself, I think it would pull atoms out of the atmosphere, soil, human body, etc. If light particles can't escape it, surely a neighboring atom must be susceptible to its pull as well. If it can't even do that much, then I don't see how it could possibly remain in a state at which it could be considered a black hole for any measurable ammount of time.
Crusher said:
The distinction you draw is pretty much the distinction between something which is a black hole and something which isn't!
The expression is correct, though you have to understand that the M is the enclosed mass, ie. the mass enclosed within radius r.
For most everyday objects what you say is true, they are larger than r. If they were smaller than r they'd be a black hole. By definition.
arjan de lumens
Veteran
Stay in school! heh
I only had 2 semesters of physics, and I don't even remember if we studied black holes specifically, but you still learn a lot of basic principles that help you understand more complex situations. I'm sure nutball has a better knowledge of them than I do, I was just trying to apply common sense and reason my way through justifying my previous claim. About the only thing I have left that would help my case would be to find the average mass of a tennis ball, determine what radius such a mass needs to be compressed to in order to create an event horizon, and then compare that size to the distance between atoms in the atmosphere to see how likely it would be to start pulling the earth into it. I don't really care about the argument enough to go that far, though.
I only had 2 semesters of physics, and I don't even remember if we studied black holes specifically, but you still learn a lot of basic principles that help you understand more complex situations. I'm sure nutball has a better knowledge of them than I do, I was just trying to apply common sense and reason my way through justifying my previous claim. About the only thing I have left that would help my case would be to find the average mass of a tennis ball, determine what radius such a mass needs to be compressed to in order to create an event horizon, and then compare that size to the distance between atoms in the atmosphere to see how likely it would be to start pulling the earth into it. I don't really care about the argument enough to go that far, though.
