# Black holes

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#### PiotrSatan

##### Guest
Why are 1mm in diameter black holes weighing as much as Moon? It doesn't even fit! I mean, how much atoms can fit in 1mm object and how much in object of size of moon? What do blackholes do that they weigh so much?

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#### origin

##### Guest
Re: Weight of black holes

PiotrSatan":87euz7ao said:
Why are 1mm in diameter black holes weighing as much as Moon? It doesn't even fit! I mean, how much atoms can fit in 1mm object and how much in object of size of moon? What do blackholes do that they weigh so much?
It is not weight it is mass. You are right it does not fit. In a neutron star the material is squashed together so there is essentially a mass of neutrons with no space between the nucleons. It would seem that this is the most compacted a material can get. The problem is that if there is more mass added to the system then the force of gravity overcomes the Pauli Exclusion (this the name of the priciple that keeps one nucleon from occupying the same space of another nucleon) and the star continues to contract until it forms a black hole. How small will the volume of the mass become in a black hole, hard to say it may go to zero volume!?!

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#### yevaud

##### Guest
Re: Weight of black holes

Exactly.

Remember, Piotr, a Black Hole contains most of the mass of the original star. It didn't vanish, it's still all there.

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#### PiotrSatan

##### Guest
Re: Weight of black holes

Yeah but on the example I imagined LHC. How come did it make miniblackholes (of 1mm diameter) didnt crush or disort Earth and how were they created? I mean come on, mass of moon?! That's god damn much! And why some black holes like in the center of galaxy actually make light and why dont they just eat up all the surrounding galaxy stars just "stand" in place.

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#### yevaud

##### Guest
Well, below a certain mass-limit, Black Holes are impermanent. They "evaporate" far faster than they could possibly gain mass. That's strict "Hawking Radiation" at work.

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#### PiotrSatan

##### Guest
No offence, I am only 14 and in my school year I've just learned about objects moving not any smart things like you say but in my opinion that doesn't make sense. How can a blackhole gain mass out of nothing? Doesn't it just spawn weighing as much it weights later? I mean the one in LHC.

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#### yevaud

##### Guest
Ah, I see where you're issue is. OK. Remember, strict E=MC^2. Energy is the equivalent of mass. In the case of the LHC, pumping energy into a point particle is the same as doing so by feeding it mass.

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#### PiotrSatan

##### Guest
ooooooh, that makes sense

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#### Shpaget

##### Guest
Correct me if I'm wrong, but LHC never smashed anything. It took couple of protons for a spin (a slow one), but after that broke down and is still under repair (heating/repairing/cooling it takes time) and not operational.
Considering all above, no black holes were created in CERN, and quite frankly, I don't think they ever will be. Those black holes swallowing Earth theories are rubbish.

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#### PiotrSatan

##### Guest
I know, I know but I was referring to massive mass of 1mm object, it's like some microbe had mass of whole Jupiter or something.

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#### MeteorWayne

##### Guest
Spaget, I believe that's correct, there were no collisions. The proton test was slow if you consider 99% of the speed of light slow (I don't really know the exact number)

Whether mini black holes form will be an interesting part of the science results when they get up to full power.

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#### MeteorWayne

##### Guest
PiotrSatan":20i9fr69 said:
I know, I know but I was referring to massive mass of 1mm object, it's like some microbe had mass of whole Jupiter or something.
Well, it's not quite like that. First of all, 1 mm is a LOT larger than a microbe, and a 1mm black hole won't have anywhere near the mass of Jupiter.

Edit:

"The Schwarzschild radius of an object is proportional to the mass. Accordingly, the Sun has a Schwarzschild radius of approximately 3 km, while the Earth's is only about 9 mm. That is, if all the mass of the Sun (or Earth) were contained in a sphere with a radius of 3 km (or Earth of 9 mm), then the volume of the Sun (or Earth) would continue to collapse into a singularity, due to the force of gravity."

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#### Shpaget

##### Guest
LHC never achieved 99% c.
On the first run it took the particles almost an hour to make a full circle, which would mean they were traveling slower than I ride my bike... uphill.
On the second run it was even slower (one and a half hours).
After that it broke down.

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#### MeteorWayne

##### Guest
Wow, was it really that slow? I stand corrected. I'll have to peek at the LHC site!

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#### darkmatter4brains

##### Guest
yikes, I didn't realize it was that slow either!! Well, hopefully they'll hit that half-power goal in Nov. So far so good, I think ... (is there a smilie for crossing your fingers?)

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#### MeteorWayne

##### Guest
Yes, from what I can find the CW trip was at a bit more than 27 km/hr!!

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#### PiotrSatan

##### Guest
Why are blackholes being galaxy core like big star? I mean they do spread light and they all keep the stars together instead of eating them all, how does that work?

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#### Shpaget

##### Guest
They're not. The light you see in the center of galaxy comes from the stars around the hole, not the hole itself. And the answer to "Why they don't eat the stars?" is the same as to the question "Why doesn't the moon fall on Earth, or why doesn't the Earth fall in the Sun?".
They are orbiting.

Eventually they might (probably will) fall in, but not in our lifetime.

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#### PiotrSatan

##### Guest
But moon has weak gravity field and could be captured by most of planets in our solar system and black holes have so high gravitional pulling that, I think, could eat whole galaxy, I mean how come brown dwarf resists such high gravitional pulling? Something is not right for me here.

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#### Shpaget

##### Guest
Our Moon is extremely far away from other planets in solar system, which by the way have insignificant gravity compared to the Sun.
The only object that affects the Moon is the Earth (and Sun somewhat, but nowhere near the amount the Earth does).
You see, the gravitational pull decreases with the square of the distance, meaning if you increase the distance between two objects 10 times, gravitational pull will decrease 100 times.
Since Earth and Moon are very close to each other (in astronomical sense), Earths relatively small gravity strongly affects the Moon, but as you go further away, that effect wears off and by the time you reach, for example Jupiter's orbit, it is so small it can be neglected.

You also must understand that even as you come closer to the center of the galaxy and the black hole in the middle, stars that are orbiting it are still very very far away from both each other and the black hole (a lot further than Earth from Moon, or even from the Sun).
You also must understand that relative size does not matter much.
For example artificial satellites orbiting Earth compared to Earth are a lot smaller than some stars orbiting black hole (relatively speaking of course), but they still don't fall down even though they are extremely close to it. Why? Because they are orbiting. They move pretty fast in one direction which enables them to continuously fall down without ever actually hitting the ground (without factoring in the atmospheric drag).
The exact same principle applies to stars orbiting black holes. They move forwards and continuously fall around the hole, but never hitting it.
The amount of gravitational pull doesn't matter. No matter how big it is, you only need to counter it with adequate forward motion and you're orbiting.

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#### kg

##### Guest
Shpaget":r4mili2n said:
....The exact same principle applies to stars orbiting black holes. They move forwards and continuously fall around the hole, but never hitting it.
The amount of gravitational pull doesn't matter. No matter how big it is, you only need to counter it with adequate forward motion and you're orbiting.
I think that it should be pointed out that black holes can and do gobble up matter. They do this the same way that stars form by way of an accretion disc. http://en.wikipedia.org/wiki/Accretion_disc I'm not sure the proccess is well understood but for some reason matter in such a disk looses enough momentum to fall out of orbit and onto the surface of the object it was orbiting. It also releases alot of energy in the proccess causing a fair amout of "fireworks". When supermassive black holes are gobbling up large amounts of matter this way they become some of the brightest objects in the universe. A galaxy with this proccess going on in it is said to have an active galactic necleus.
http://en.wikipedia.org/wiki/Active_galactic_nucleus

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#### Shpaget

##### Guest
I know that, but I believe Piotrs' question was "Why it doesn't happen quickly?"
I could misunderstood him, but I tried to avoid talking about physics of space and time in close proximity of the black hole on purpose they're pretty complicated and don't apply at reasonable distances.

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#### PiotrSatan

##### Guest
So in conclusion black holes do not swallow surrounding stars because its fat *butt* is too lazy?

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#### MeteorWayne

##### Guest
Piotr, Please let's try and not get too silly in the Physics forum, oK?

And no, it's not due to laziness, it's due to the Newtonian laws of gravity that have been known for centuries. Until you get VERY close to a black hole, a large mass is just that, a large mass. If the sun was shrunk to the size where it would become a black hole (~ 3 km in diameter) we at the earth's distance would notice no change in our orbit, since the same amount of mass would be at the center of the solar system. Of course the sun would be invisible, but we'd continue orbiting along on our merry way..

Wayne

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#### PiotrSatan

##### Guest
If the sun was black hole that means we would have no light BUT however we would be still in orbit and we would be fine? Wow awesome well that's so far everything I wanted to know.

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