1 - What would happen if a black hole passed in front of the earth and between the sun; or in such a way that a huge light source is behind the hole and shining on us? I’m not interested in the possibility of the earth being sucked in (assume Venus was replaced by a blackhole of similiar mass, for example) but only of what it would LOOK like when in front of the sun.
I would assume that the light going near it would be pulled in, but as the light became further and further away that it would eventually have to reach us. Would it appear as a heavily distorted black sphere? Or something more exotic?
2 - I was reading the recent article in Scientific America about black hole computers, it was fascinating yes…but the main thing I couldn’t wrap my mind around was such small black holes. I had always assumed that black holes had to be fairly large, at least planet sized…but subatomic? Or the size of a marble? I have trouble wrapping my head around such an idea.
What would happen if I touched a marble sized blackhole? Or a subatomic one? Would I just be compressed and die a horrible death? How far out would its gravity go? How much STUFF would have to be in there? I’m having trouble visualizing how that would work.
3 - Can you reverse a blackhole into ‘normal’ matter? Could you somehow cut or cleave it in half or whatever so that it doesn’t have enough mass in enough space to be a black hole?
4 - What happens if two black holes collide? Would they simply join into one larger black hole?
5 - During the Big Bang all the matter we have today was compressed into a single point – why did it not collapse into a black hole immediately?
A marble-sized black hole would have the mass of a largeish mountain, IIRC, so it would just sink to the core of the Earth and sit down there forever.
It’s not correct to think of a black hole as a cosmic vacuum cleaner. They do exert a tremendous gravitic force, but that’s entirely due to their mass. A larger object with the same mass would have the same gravitic force.
I’m guessing here, but I don’t think a black hole with the mass of our Sun ocould even get near our Solar System without causing mucho Chaos. From what I’ve read, these things are most powerfull. :eek: Chronos?
Ignoring the orbital effects of a black hole between us and the sun, the black hole would affect the light from the sun in a way similar to what a huge magnifying lens would do.
Um, you may be thinking about one with a Schwarzchild radius comparable to the regular radius of the Sun. Any object of a given mass “feels the same” to a remote observer. That is: a black hole with the mass of the Sun in the same place the Sun is now would feel the same as far as gravity goes.
As for the OP (replace Venus with a black hole of the same mass (same principle applies)) I’m not sure what sort of lensing would go on. IIRC, the “radius” of the hole would be twice the mass of Venus in “geometrized units”. That is, given a mass of 4.8×10[sup]24[/sup] kg and a conversion factor of 0.74×10[sup]-24[/sup] mm/kg, the hole would look to a remote observer like it was about seven millimeters across. Pretty tiny, considering.
A black hole is just a region behind an event horizon, where the curvature of spacetime is sufficiently high to prevent light (or anything else) from escaping. Black holes generally will only form from stellar collapse when the star is sufficiently massive, yes, but the theory doesn’t care how it formed.
Nope, you pretty much have to wait until it “boils off”. Remember, it’s not a “thing” so much as a region of spacetime things can enter, but can’t get out of.
Yep. In fact, there are many results on this sort of thing. Among other things, the surface area of the resulting hole has to be larger than the sum of the surface areas of the original holes.
I’m not sure how to answer this without a few semesters of differential geometry. I’ll defer to Chronos.
That actually touches on a longtime question I’ve had… what would happen if a black hole of less than astronomical mass (yours with the mass of a largeish mountain) was loose on earth without any magnetic or other form of containment…
sinking down to the core of the earth I’d agree with… but is that all of it? I would think that…
down in the core of the earth “Blackie” (to give it a name) would find lots of dense liquid iron… wouldn’t it slurp this up, slowly, only the stuff near it, but gradually absorbing all of it that was available?? (I know that the hole would not remain motionless at the exact center, it would drift a lot, but as long as there was any material in the center of the earth, it and the hole would be drawn towards each other, right??
Now, what would happen to the earth without the pressure of the core occupying the space that the core used to take up?? Wouldn’t other parts of the earth, the semi-solid mantle, begin to come loose, fall down, and a lot of them would, slowly at first, get eaten by Blackie. By now the black hole would have an appreciable fraction of the earth’s mass by this point after all.
Eventually, I guess the crust of the earth would rupture, pieces of it (along with the air in our atmosphere and the water in the oceans) would fall down into the void, and finally the rest of the crust would crack into little pieces, bump against each other, and eventually everything would be consumed. The moon and a bunch of artificial satellites would continue orbiting a black hole with the same mass as the earth.
Am I wrong here?? Have I made some fairly obvious misinterpretation of the way this black hole would behave? If so, then please explain.
I don’t have any idea; but what I’d got the impression of by listening to physicists talk was that ‘all at a point’ was a simplification. That is, none of our increasingly unified theories can yet say what exactly happens when space is compressed that much, but that as of fractionally after it was expanding fast enough that it could escape the gravitation for at least, say, 15 bln years Um.
I’ll try to tackle this one, though IANAP (physicist.) As I understand it, nobody’s entirely sure, but the characteristics of the big bang are such that the matter of the universe had such enormous heat and kinetic energy that the universe was immediately expanding, despite the (also enormous, but by definition less enormous) force of gravity working to contract so much matter in such tight quarters.
as far as the question of ‘what could cause matter to fly out of a single point spontaneously’ – that’s an imponderable, so far. Just about no physics or math we have is capable of describing the pre-big bang state of existence or what could have triggered the transition from pre-big-bang into the big bang. (Especially since it seems to work out that time only began with the big bang and did not exist before it.)
You’re still thinking of a black hole as a cosmic vacuum cleaner. I don’t know how much of the Earth it would absorb, but probably not as much as you might think.
Mind you, it would near double the mass of the Earth, which could cause us to go crashing into the sun (that’s bad), but I’m not sure about that.
Okay… not quite understanding in what way it isn’t enough of a vacuum cleaner to follow through that whole scenario. I understand that a black hole isn’t able to ‘suck up’ anything that it couldn’t pull close to itself with the force of gravity and its own mass, but even a really tiny black hole would be able to ‘drink fluids’ that come close to it, right?? There’s no limit on how much matter it can absorb, and how much mass it can gain that way, except for how much fluid matter is available.
On the other hand, maybe I’ve made overestimates on how much the stability of the mantle would be affected by the absorption of the core, and/or whether our black hole, with the mass of the core of the earth, would be able to break down large chunks of solid rock. (or semi-solid rock at any rate.) Is that the problem??
I’m actually not sure what you mean by ‘marble sized black hole’ - as I understand it, all black holes are less than the size of the head of a pin, and the more massive they get the SMALLER they actually are. I would imagine that if you touched a fairly ‘light’ black hole it would probably feel very much like a pinprick, though that’s just a wild guess. (Wonder how massive it would have to be before you’d have to worry about losing a finger… or if that’s even an option, and by that point it would be massive enough that you couldn’t approach it safely without being in some kind of protective harness.)
I think we were wondering why the mass of the earth would increase by any appreciable fraction. (Compared to the mass of the earth while the black hole was still on the surface in some kind of containment field, say.)
I think so, though it’s a little tough to even talk about size with black holes.
It’s common convention to talk about the ‘size’ of a black hole as the size of its event horizon. Even so, your ‘black hole the size of a marble’ would be, apparently, the mass of the earth. (Schwarzschild radius of less than 2 centimeters, 0.7 inches.) Okay, maybe a big marble.
Massive black holes with many times the mass of the sun would have even horizons as big as small asteroids or planets, certainly, maybe even larger.
What I was saying about the size of the hole was talking about the actual mass singlularity at the core of the event horizon… and even that’s just a guess, since we can’t see inside. (However, the event horizon would behave differently if the mass of the hole were spread evenly through it, I would think.)
It would make the sun appear as a ring. The more massive the black hole, the larger (but thinner) the ring would be.
I imagine if you touched a marble sized black hole, you would be sucked in quickly. Do remember that the radius of the black hole is the distance at which light cannot escape. The gravity doesn’t suddenly stop there and humans are affected more by gravity than light. Frankly, I wouldn’t want to be within several miles of it.
As for a marble-sized black hole sucking up Earth, it would almost certainly happen. Part of the reason is explained above. It would exert a lot of gravity on anything nearby, far more than just an inch or two. Plus, since the core is liquid, it would basically flow into the black hole. And without the core, I would be very surprised if the mantle and crust didn’t collapse.
Nope. The “no hair” theorem says all you can tell about a black hole is its mass, angular momentum, and charge. The distribution inside is immaterial, though the normal model has everything getting sucked to the “center” very quickly.
Depending on its size, the black hole would act as a (gravitational) lens, and you’d see various rings and arcs where the sun’s light was refracted. A marble sized hole would likely be too small to produce effects you could see on earth, but a large hole at just the right size and distance might focus a goodly fraction of the sun’s output directly on the earth’s surface. That would be bad.
Here are a couple of simulations of the light bending ability of black holes: Virtual View of a Black Hole A Black Hole Bends Light
Um.