Impossible for a star to light up on its own?

In order for a star like ours to be born we have to have lots of hydrogen, the most plentiful element in the galaxy, and alot of heat. The hydrogen collects due to gravitational forces. As the gravitational forces cause the hydrogen to compress, the hydrogen heats up. As the hydrogen heats up it expands with a much greater force than the gravity that holds it together...and as the hydrogen expands it cools off. Since nature tends to equalize things at the lowest energy level possible, how in the universe could a star ever be born? Guys I run around with don't have stuff like this on their mind. Got any comments?

 

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Cable,

Trust me, de expension force of the hydrogen gas is not greater then the gravitational pressure. It takes nuclear fusion to provide enough outward pressure for a star with the weight of our sun to not to be turned into a black hole...

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I err, therefore I exist !

 

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Plato,
To continue in my thought process, our sun does not become a black hole because the heat created by nuclear fussion causes gas expansion that overpowers gravity to a degree. I submit, following this same thought process that nothing can fall into a black hole untill it has lost enough energy to do so. A fired up star with lots of energy would not be able to become a black hole. To make a comment regarding the original question...some friends and I made a fire on the edge of a limestone quarry one night. We lined the fire with limestone rocks. They had a lot of moisture in them. You could imagine our surprise when the rocks started exploding. I think of that and think of your comment and say that the power of heated gases, expanding, is no small power. I submit that it is much easier to make a black hole than it is to make a star.
I stand by my original question. In order to prove the claim right or wrong I have to come up with some answers. How strong is the power of a gas heated? How strong is the power of gravity? Do their respective powers change nonproportionally at greater pressures or temperatures? Thank you for your response Plato. The only starting point I have today is pv=k (Boyle's Law), and gravity on earth accelerates freefalling objects at 32ft/sec/sec. How do I put this together?

 

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Cable,

I think what you need is the inverse square law of Newton and the ideal gas law. The gravitational force F_G = G*M*m/r^2 and the ideal gas law : PV = NRT. P is pressure and this is the same as F_P/r^2, force per square meter. V is of course r^3, a volume. So the ideal gas law becomes F_P/r^2*r^3=NRT which can be reduced to the form F_P = NRT/r.
You can see that while the gas is contracting (r getting smaller) the gravitational force F_G increases much faster then the pressure force F_P which can be thought of as a repulsive force.

So you see that if there was no such thing as fusion power, a star would collapse under its own weight...

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I err, therefore I exist !

 

Actually, a star like the Sun would never become a black hole; if it weren't for fusion the Sun would be a neutron star (the electrons would be squeezed onto the protons to create neutrons, but the neutrons will still repel each other with sufficient force, called degeneracy pressure, to prevent complete collapse. The pressure arises out of the uncertainty principle: as the neutrons are squeezed closer together, they are being confined to increasingly tight quarters, and must compensate for the increasingly exact position with increasingly randomized momentum -- in other words, they vibrate violently.) It takes 1.4 solar masses (the so-called Chandrasekhar limit) to overcome the neutron degeneracy pressure at the star's center and trigger the complete collapse toward a singularity.

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I am; therefore I think.

 

Plato, that's great! I won't be back for awhile. It will take 2 to 4 weeks to get comfortable with what you just scratched out. In two to four weeks I'LL BE BACK! Boris you're way over my head, but I could get used to it.


[This message has been edited by Cable Man (edited June 07, 2000).]

 

Boris,

I hate to do this to you but you are actually one step to far. Everything you say is correct but you should switch neutronstar with white dwarf and black hole with neutronstar. The Chandrasekhar limit is actually the maximum mass a star can have to become a white dwarf, if it has more mass it will become a neutron star. The next limit is 3 solarmasses then nothing can stop the gravitational collapse.

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I err, therefore I exist !

 

Oopsie, got things mixed up a tad, didn't I? Guess that's what happens when you try to recall things you haven't touched for years, without checking the references... Good call Plato.

Hmm, Plato, remember that time we discussed effects of compression and interference on memory recall? I think you just got one juicy demonstration!

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I am; therefore I think.

 

Neat website Plato! Love that stuff! You and Boris
are talking about the death of a star. I'm referring to the creation of a star. When a star is burning the energy released as heat excites gas atoms which causes them to expand greatly which prevents the star from collapsing in on itself.

Where did the heat, which was necessary to create the initial fusion reaction, come from? As dust and gas particles collect to form a sphere gravity builds. As pressure builds so does heat. As heat builds atoms move around alot more...become farther apart...and cool off. Also, heat caused by compression is lost into space. I submit thru intution that star formation had to be fast, in order not to loose necessary heat energy, and the building blocks had to be moving into each other at speeds greater than gravitational attractional in order to overcome expansion caused by heat.

((inverse square law)+(ideal gas law variation))/(change in time)=temperature and pressure required to start chain reaction fusion reaction.

Need to find out...

What are minimum temperatures and pressures required to start fusion reaction with hydrogen?

How fast is heat lost thru hydrogen gas?


FP=NRT/r...FP=NRT/r...FP=NRT/r...

Still chewing,
Cable Man

 

Hi Cable Man,

The birth of a star is pretty much the way you described it. Gravitational contraction of a dustcloud (eg. hydrogen) builds up the temperature due to friction processes, high pressures,... and allows nuclear fission to start.

The gravitational pull is stopped because of the so called "radiation pressure". Einstein's theory of relativity predicts photons have momentum, and all the momenta of the photons exercise a pressure on tha matter within the star, causing it to expand again. This expansion is stopped however, once again due to gravitational interactions, so at a certain moment there's a delicate equilibrium between the gravitational forces that tend to pull the star together and the radiation pressure, trying to tear it apart.

Heat does not cause the expansion. It is true that higher temperatures correspond with higher kinetic energies of the particles, but this does not necessarily mean they move faster (there's also energy in the rotational and vibrational modes of the particles).

Also, heat cannot "flow away" from the forming star since there's no matter to carry the heat away ("heat" is only a form of energy that requires a medium to dissipate in).

And finally, I am not sure whether the ideal gas law is adequate in these extreme situations of high temperatures and high pressures, but this is merely a guess from my side since I have no clue - yet - how astronomers calculate that kind of stuff

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Bye!

Crisp


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"The best thing you can become in life is yourself" -- M. Eyskens.

 

Hi Crisp!
If heat can only radiate away within a medium then why do we cool off at night? I've never heard anything quite like you said it. The earth becomes colder faster on clear nights and stays warmer on cloudy nights. If heat is not disappearing what is?

You say heat corresponds with higher kinetic energies but doesn't necessarily mean expansion. I submit it does mean expansion unless a greater force is acting out here, like higher pressure or something. Am I missing something? Could you go into a little more detail?

 

Actually heat can radiate without a medium, this is done by emission of photons. Cooling of is called back body radiation, it is a universal property of matter. The equation was found exactly 100 years ago by Max Plack and constituted the beginning of quantum theory. Plack found that this radiation was not continuous but in packages of an integer number times the planck constant times the frequency of the radiation.

What you are after, Cable is the formula for a self gravitating body. Self gravitation means that there is enough mass in a volume of interstellar gas to keep everything together. This will result in a contraction of the gas towards its mass middle point. This contraction means that gravity produces a labour this is seen with the formula : A = F.delta(r) with the displacement delta(r) in the same direction of the force F. This labour is actually energy that is generated, it is mainly this energy that is responsible for the heating of the gas. Of course this heating is felt most close to the mass middlepoint, where the concentration of gas is the highest. It is there that the first fusion reactions are started once the density and temperature are high enough.

I belief I read somewhere that the mass threshold for a star to ignite is something like 40 or 50 Jupiter masses or about 0.05 sun masses. However don't quote me on these figures

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I err, therefore I exist !

 

Hi Cable Man, Plato,

Plato: Yes, I knew I forgot to mention something in the reply. Thanks for bringing that to my attention

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... However, cooling off due to black body radiation is not what I ment in my previous reply, I was referring to the loss in energy caused by collisions of atoms in a medium and the object that cools off.

Now Cable Man,

Actually I never heard of cloudy nights being warmer than clear nights - but then again, you don't live where I do

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. Now I have absolutely no idea why the earth gets colder at night (that is to say, where all the heat goes). The earth's atmosphere is a very complex mechanism and I have absolutely no idea how it works.

What I do know is that if you solid objects don't cool off in space as they do on earth. The reason why objects cool off on earth is because energy is transfered away to the medium those objects are in (eg. air). Heat itself cannot flow away, since this would mean that heat is something you can grab onto; it's all a transfer of energy and the only way energy can be transferred is in the form of photons (like Plato mentioned) or in a medium. So heat from a forming star is not lost into space because of some wierd mechanism; the moment the star ignites, the only way it can cool off is by emitting light. (that was the point i was trying to make all along).

About heat causing expansion: yes, for only a few liters of gas, heating up causes expansion on earth. But if throw together 10^30 kg of hydrogen gas, then there won't be any expansion because of heat building up, simply because gravitational forces are a lot stronger. The expansion will be caused by radiation pressure (which, then again, is a direct consequence of heat building up ofcourse) but the formulas you use to describe this process is not simply PV = NRT

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Bye!

Crisp


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"The best thing you can become in life is yourself" -- M. Eyskens.

 

Hey Cable Guy:

 

Hey Cable Guy:
If you really want to hear(read) how stars are formed, like ours for instance.I suggest that you go to this link: www.urantia.org . There are some people who say that this book is full of junk science, I on the other hand have found it to be quite reputable. Some of the information expressed in this book (45 yrs. ago) is just now being discovered by scientist and much of it has been verified.There are many questions you might have about the origin of this book and who the authors are.If you search the site empirically you will see the answers. If you wish I can send you more links, one is where you can read the book online and another is full of art inspired by the books teachings. No matter what anyone says, it is not a religion or a cult, just a source of revelation. Give it a try.

Paul/Machiaventa

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Still waiting on your definition of the word "religion".



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The sky is not the limit, nor are the stars.

 

Mr.Lenny:
I do not wish to debate you, but just what do you think is the definition of a religion?
To me a mordern religion is something that is organized in order to benfit it self more than mankind.Pre- modern religions would be those which were organized to control their followers and keep them in the dark. Which inturn keeps them in control and able to define what is correct and what is not.
We at the foundation only wish to present a possible alternative to both paradigms.There fore leaving up to the reader to choose for himself which is right for them. We only believe that personality is the only true religion, and that all else is only portrayed for the publics benefit.Say what you will, but there is no devil and there is no hell except what we make for ourselves here on Urantia.

Paul/Machiaventa

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[This message has been edited by paul defourneaux (edited August 24, 2000).]

 

Can’t say as I blame you.

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I pretty much agree with the dictionary:


re·li·gion (ri lijÆÃn), n.
A set of beliefs concerning the cause, nature, and purpose of the universe, esp. when considered as the creation of a superhuman agency or agencies. (Random House Unabridged Dictionary Second Edition, Copyright © 1996, 1993, 1987, by Random House, Inc.)

Now, what part of that definition does not describe Urantia?

All great religions have as a common aspiration, the benefit of mankind at their core. Whether it be the salvation of the soul as is central in Christianity or the ordering of society as is dominate in Confucianism, the betterment of the person and/or society has always been the aim. True, as often as not these goals have been only been partially achieved throughout history and many have suffered in the name of religion. However even from a purely humanistic point of view, a strong case can be made for the idea that society would have never evolved above the primitive without the influence of the great religions of the world. Our system of laws, our art, and our music, and our literature can all be traced to their roots in religion. We would probably still be in the caves (or tree-tops) without the cultural influence of the great religions of the world. Now just what has the Urantia cult contributed to our culture?

You seem to be quite fixated on the subjects of hell and the devil. I believe it was C. S. Lewis who said that Satan’s greatest deception is to convince mankind that he does not exist and that his second greatest deception is to exaggerate his importance and power.

Concerning the subjuct of hell: If you are correct it will make no difference after our deaths. If I am correct it will make a great deal of difference. Are you a gambling man Paul?



[This message has been edited by Lenny (edited August 25, 2000).]

 

Lenny:
I am not but you seem to be. They got you so brainwashed and scared that you feel the only way is theirs.THERE IS NO GAMBLE, when one knows the truth, do you? If you did you would not be so scared of a place that does not exist, except in your mind.

Paul/Machaiventa

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The Mind/Soul is the first source and center of all reality: Stephen Beam

 

"C. S. Lewis who said that Satan’s greatest deception is to convince mankind that he does not exist and that his second greatest deception is to exaggerate his importance and power."


So? It doesn't matter what he said. Did he write the bible?