Black holes

[dani]

I'm doing a science project about controversy on black holes, and though any information on them in general would be appreciated, I'd like to focus more on whether or not one could ever engulf our galaxy and virtually "eat" it or not, and what might happen if it did. Any help on this would be greatly appreciated!

[RyanJ]

I'm doing a science project about controversy on black holes, and though any information on them in general would be appreciated, I'd like to focus more on whether or not one could ever engulf our galaxy and virtually "eat" it or not, and what might happen if it did. Any help on this would be greatly appreciated!

 

 

Well, its a common missconception. For example if you replaced the sun with a blach hole of equal mass it would not pull in the planets because its still the smae mass.

 

It is not knows wether or not black holes actually exist but there have been experiments that have found evidence of gravitational lensing, an effect that is thought to be caused by a black holes extreme gravity where the light is bent towards the event horison.

 

Black holes are potentially very interesting and a lot of developments in their theories have been madfe in the last few years by people like Stephen Hawking who for example has proven that black holes can evaporate through what is called Hawking radiation.

 

Black holes themselves are basially a star that has collapsed beond a boundary called the event horison. This is the point at which the gravity of the star has such an effect that going beond that means you simply cannjot escape due to the way space and time are distorted.

 

At the heart of a black hole is a point called a singularity, this is the point at which time and space no longer exist - its a point of infinate density and infinate smallness, its also the point at which our current understanding breaks down.

 

If you want to do research I really suggest you look at Wikipedia, it has a page full of interesting facts that may help you.

 

http://en.wikipedia.org/wiki/Black_holes

 

Also, of additional interest:

 

http://en.wikipedia.org/wiki/Worm_holes

http://en.wikipedia.org/wiki/Neutron_star

http://en.wikipedia.org/wiki/White_hole

 

Cheers,

 

Ryan Jones

[timo]

Well, its a common missconception. For example if you replaced the sun with a blach hole of equal mass it would not pull in the planets because its still the same mass.

That is, if you replace it with a black hole of the sun´s mass.

 

It is not knows wether or not black holes actually exist but there have been experiments that have found evidence of gravitational lensing, an effect that is thought to be caused by a black holes extreme gravity where the light is bent towards the event horison.

As you indirectly said in the previous paragraph, the gravitational effects created by a black hole and the gravitational effects created by any other spherical symmetric obejct with the same mass are the same - with the little difference that a black hole is smaller and you therefore can get closer to get really strong effects. I think gravitational lensing has been observed on our sun, not on black holes.

 

Blak holes are potentially very interesting and a lot of developments in their theories have been madfe in the last few years by people like Stephen Hawking who for example has proven that black holes can evaporate through what is called Hawking radiation.

I am not sure if Hawking Radiation is more than a handwaving hypothesis. But I don´t know much about it anyways; I´m just a bit cautious when the name Hawking is mentioned because there´s a lot of hype about him.

 

Some random remarks for the original question:

- Up to today, there is no real (experimental) proof that black holes really exist.

- As mentioned above, the gravitational effects of a black hole and any other spherical symmetric mass distribution (sun, planet) are the same - with the exception that a black hole is small enough so that you can get as close as to reach the "event horizont", an area where some strange effects happen.

- Therefore, as a first guess I´d say that the chance of a black hole eating of a whole galaxy is as big as the chance of a planet of equal mass attracting a galaxy to it (in the sense of "all the stars/planets bash into that planet because they are attracted by it).

- There´s one difference in the analogy of the previous point. For planets/suns, there´s the tendency to release part of the attracted mass by whatever process. In the sun it´s light created by fusion; supernovae also play a role, I think. For black holes, there is no such process known except for the Hawking Radiation RyanJ mentioned.

[[Tycho?]]

There is quite a lot of evidence that suggests they do indeed exist. If they dont, then some other super dense must exist which we dont know about.

 

Look it up on wikipedia, they have info on the evidence to support and go against black holes.

 

It should be noted though that the vast majority of the scientific community consideres them to exist.

[RyanJ]

']

It should be noted though that the vast majority of the scientific community consideres them to exist.

 

Well, it makes sence... something collapses smaller and smaller untill there is no known force that can hold back the collapse.

 

This was a long debate, a good book to read on it is called Black Holes and Time Warps.

 

When a star is in mid life its forces are ballanced, gravity trying to crush it and its internal reactions trying to make it explode are equal. To the end of its life the stars starts to run out of fule and so its internal force is decreased. As this occurs the gravity overpowers it and compresses it.

 

Assuming the star does not expode this will form a neutron star, the electrons were forced into the protons making neutrons. This can only happen within a limit, if the star is bigger the a limit (of which I forget the name) then the repulsive force of these neutrons is no longer strong enough to hold of the collapse, the star shrinks past the Schwarzschild radius forming an event horizon, then into a singularity.

 

One of the funny things is that as the star crosses the Schwarzschild radius it will appear to freeze, thus their former names, frozen stars. Even though if you were on the surface of the star you would see it progress as normal but thats a relativity effect.

 

Cheers,

 

Ryan Jones

[timo]

Assuming the star does not expode this will form a neutron star, the electrons were forced into the protons making neutrons. This can only happen within a limit, if the star is bigger the a limit (of which I forget the name) then the repulsive force of thes electrons is no longer strong enough to hold of the collapse, the star shrinks past the Schwarzschild radius forming an event horizon, then into a singularity.

I think the main force resisting a complete gravitational collapse is due to the fact that neutrons are fermions - but I have to say that this is just a guess the name "Neutron star" suggests to me.

Being fermions they must occupy a seperate state, each. As a good approx, this will be all of the lowest states. With decreasing volume, the energies of the states grow, so the total energy of the neutrons must grow. Because of that, it takes energy F*dr to compress a sphere of fermionic gas by dr (r is radius, here). You can associate this with a force F resisting compression.

 

@[Thyco?]: I didn´t say there is no evidence for black holes. And perhaps saying there is no real experimental proof was not a good idea, too. It´s a bit up to debate where the lines between "real experimental proof", "strong evidence", "evidence" and "indirect evidence" lie.´I just wanted to say that E.g. atoms are on a more solid ground than black holes.

[RyanJ]

I think the main force resisting a complete gravitational collapse is due to the fact that neutrons are fermions - but I have to say that this is just a guess the name "Neutron star" suggests to me.

Being fermions they must occupy a seperate state' date=' each. As a good approx, this will be all of the lowest states. With decreasing volume, the energies of the states grow, so the total energy of the neutrons must grow. Because of that, it takes energy F*dr to compress a sphere of fermionic gas by dr (r is radius, here). You can associate this with a force F resisting compression.[/quote']

 

Sorry - should have been neutrons. Corrected

 

Cheers,

 

Ryan Jones

[Daecon]

If there was a black hole with the size of the Sun, how big would the Event Horizon be?

 

I thought I heard that the diameter of a Black Hole of Solar mass would be the same as the diameter of Earth... is this true?

[[Tycho?]]

If there was a black hole with the size of the Sun' date=' how big would the Event Horizon be?

 

I thought I heard that the diameter of a Black Hole of Solar mass would be the same as the diameter of Earth... is this true?[/quote']

 

Look up the schwarzchild radius and you can calculate it. I'll do it just to get a number, but the forumla is a simple one.

 

edit: so the equation is r=2Gm/c^2

where G is newtons gravitational constant = 6.67e-11

m is mass of the sun = 2e30 kg

c is the speed of light = 3e8 m/s

 

so I get just shy of 3km for the radius.

[[Tycho?]]

I think the main force resisting a complete gravitational collapse is due to the fact that neutrons are fermions - but I have to say that this is just a guess the name "Neutron star" suggests to me.

Being fermions they must occupy a seperate state' date=' each. As a good approx, this will be all of the lowest states. With decreasing volume, the energies of the states grow, so the total energy of the neutrons must grow. Because of that, it takes energy F*dr to compress a sphere of fermionic gas by dr (r is radius, here). You can associate this with a force F resisting compression.

 

@[Thyco?']: I didn´t say there is no evidence for black holes. And perhaps saying there is no real experimental proof was not a good idea, too. It´s a bit up to debate where the lines between "real experimental proof", "strong evidence", "evidence" and "indirect evidence" lie.´I just wanted to say that E.g. atoms are on a more solid ground than black holes.

 

Oh, yeah my post wasn't a resonse to yours or anything, I posted before I read the rest of the responses. But your point is taken, black holes are not on as strong a ground as other many other things in physics (like atoms).

[EvoN1020v]

Would you say that a black hole have antimatter particles? Because I got some interesting information on antimatter. It's pretty shocking.

[Daecon]

I would have thought that even if a Black Hole had some antimatter in it, it would react with the standard matter and become energy, which still wouldn't be able to escape the Event Horizon, so it would make no difference...

[RyanJ]

I would have thought that even if a Black Hole had some antimatter in it, it would react with the standard matter and become energy, which still wouldn't be able to escape the Event Horizon, so it would make no difference...

 

Well, not really... inside a black hoe and at its singularity mater, space and time do not exist - they are crunshed into a single point. For this I guess you'd need an anti-singularity...

 

I have a question. Nothing according to quantum mechanics can have its speed and position neaured at the same instant. At the heart of the singularity, we havea point of infinite smalness, does that not mean we can say with certaintly that is where the particle is? Or does it not apply in this case due to the extreme nature insidethe black hole?

 

And here is the Schwarzschild radius formula in LaTex for clarity.

 

[math]r_{\rm S} = {2\,Gm \over c^2}[/math]

 

Cheers,

 

Ryan Jones

[EvoN1020v]

Regardless, I found this interesting information on antimatter particles:

 

[math]\rightarrow[/math] The world's largest scientific research facility --- Switzerland's Conseil Europeen pour la Recherche Nucleaire (CERN) -- recently succeeded in producing the first particles of antimatter. Antimatter is identical to physical matter except that it is composed of particles whose electric charges are opposite to those found in normal matter.

 

Antimatter is the most powerful energy source known to man. It releases energy with 100 percent efficiency (nuclear fission is 1.5 percent efficient). Antimatter creates no pollution or radiation, and a droplet could power New York City for a full day.

 

There is, however, one catch...

 

Antimatter is highly unstable. It ignites when it comes in contact with absolutely anything... even air. A single gram of antimatter contains the energy of a 20-kiloton nuclear bomb --- the size of the bomb dropped on Hiroshima.

 

Until recently antimatter has been created only in very small amounts (a few atoms at a time). But CERN has now broken ground in its new Antiproton Decelerator --- an advanced antimatter production facility that promises to create antimatter in much larger quantities.

 

One question looms: Will this highly volatile substance save the world, or will it be used to create the most deadly weapon ever made?

 

[stored from Angels & Demons by Dan Brown]

[Daecon]

One slight, tiny little mistake, if the antimatter touches some matter by accident - BOOM!

[EvoN1020v]

Hahaa, I don't know how those scientists at CERN are able to make the antimatter. I assume from this machine (Antiproton Decelerator), they are able to do that.

 

Maybe you can do some research on the machine, and it might tell you why it won't BOOM! like you said in the post above.

[[Tycho?]]

Regardless' date=' I found this interesting information on antimatter particles:

 

[math']\rightarrow[/math] The world's largest scientific research facility --- Switzerland's Conseil Europeen pour la Recherche Nucleaire (CERN) -- recently succeeded in producing the first particles of antimatter. Antimatter is identical to physical matter except that it is composed of particles whose electric charges are opposite to those found in normal matter.

 

Antimatter is the most powerful energy source known to man. It releases energy with 100 percent efficiency (nuclear fission is 1.5 percent efficient). Antimatter creates no pollution or radiation, and a droplet could power New York City for a full day.

 

There is, however, one catch...

 

Antimatter is highly unstable. It ignites when it comes in contact with absolutely anything... even air. A single gram of antimatter contains the energy of a 20-kiloton nuclear bomb --- the size of the bomb dropped on Hiroshima.

 

Until recently antimatter has been created only in very small amounts (a few atoms at a time). But CERN has now broken ground in its new Antiproton Decelerator --- an advanced antimatter production facility that promises to create antimatter in much larger quantities.

 

One question looms: Will this highly volatile substance save the world, or will it be used to create the most deadly weapon ever made?

 

[stored from Angels & Demons by Dan Brown]

 

I wont comment on that post, since this is supposed to be a thread about black holes. I'll point out the things wrong with this article if you make a thread about it.