Please Explain Why:

[Quartile]

The earth wasn't a star at some point in time and has coalesced (as stars do) through its stages of stardom all the way to its current state.

 

In other words, what happens to dwarfs after they "die"?

[Daecon]

Because it never had enough mass to create enough density/pressure for the body to ignite to begin with.

 

What happens to dwarfs after they die? The same thing that happens to any other burnt-out cinder: Nothing.

[Quartile]

Ignite?

 

Explain our molten iron core in a way that excludes the possibility that Earth is a star, still involved in fusion. Our inability to observe processes that last millions of times longer than we do allows room for the philosophical proposition that since stars and planets are made of the same thing, they are the same thing. I think this philosophical proposition may have physical credence.

 

 

Will someone with a good understanding of fission/fusion tell me why this isn't possible?

[Daecon]

Well I think that comes down to a semantics argument of what the word "star" refers to in cosmological language.

[Edtharan]

Will someone with a good understanding of fission/fusion tell me why this isn't possible?

The problem is Heat and Gravity. You are probably aware that when you heat up most substances they expand. To initiate fusion you need a very high temperature.

 

Now heat is usually expressed as the particles moving faster (in a solid they vibrate faster - at high enough temperatures they will then vibrate so fast that they will break off from the solid, this is called melting). In a fluid (gas or liquid), the particles are free to move around and this heat is expressed as the velocity of the particle. It is this reason that substances expand when heated. If you heat a liquid enough the particles have enough velocity to escape the mass, this is called evaporation (and the liquid will become a gas).

 

That is all pretty basic stuff (but as I don't know what you know I have to cover it).

 

Now, with Gravity, there is a property called Escape Velocity. This is the minimum speed which an object must have to permenently escape the gravitational pull of the object. FOr Earth this is around 11km per second (or around 39600km per hour - what would the speeding ticket you'd get for that be like ).

 

To get Earth to the point of Fusion you would ahve to heat it up quite a bit. First, it would turn all the rocks and solids to liquids, then gas. However, the particles that would exist at this point would have enough velocity to exceed the Escape Velocity. Therefore if you were to heat up the Earth enough to reach fusion temperatures, it would blow it's self apart before you got to the requiered temperatues. This means that if the Earth actually exists, then it can't have reached a temperature high enough to sustain a fusion reaction. Without that sustained fusion reaction, it could never have been a start.

 

However, if there was a star that blew apart (that is the temperatures reached during fusion were high enough to fling matter off an object with a higher mass - and therfore gravity - than Earth), then this matter would move out into space and begin to cool. At which point the velocities of the paricles would drop below the escape velocity of the gas cloud, and it would begin to condense.

 

There might be enough mass to form another star (although smaller than the first one) and part of the mass of this gas cloud might not fall into the star but swirl around it. Eventually this gas would condense into dust, planitisimals, and then planets.

 

However, as these planets would have far less mass than the first star, if they ever got to the temperatures needed to sustain fusion, they would blow them selves apart first.

 

One other point about Gravity (and this is why a planet will not get hot enough to initiate fusion):

 

When a gas cloud contracts to form a star, the heat needed to initiate fusion comes from gravity. When you compress a gas it heats up (and if you expand a gas it cools down). So as the Star contract under it's own gravitational pull, it will heat up.

 

But...

 

When you heat up a gas it expands.

 

So, if the gravity is strong enough to overcome the expansion do to the building up of heat, then it can become hot enough to initiate fusion.

 

However, if the gravity to too weak, then as it contracts, and heats up, the pressure from the hot gas will prevent it from contracting. It will slowly radiate this heat out into space as electromagnetic radiation (most likely infrared radiation). Then as it cools this way, it will again contract and heat up again.

 

This cycle will repeat until the physical integrity of the matter that make the could is enough to brace it against the gravitational pull, at which point it will no longer contract.

 

This means that objects smaller than a certain mass will never get hot enough to initiate fusion. Earth is well below the size for this to occur. In fact Juptier is far more massive than Earth, and it is not massive enough to intiate fusion. However, with Jupiter, its gravity is still causeing it to contract and heat up with this heat radiating out into space.

 

Because of this Juptier actually radiates more heat that it recieves as the heat caused by it's contraction is being radiated out as infrared radiation.

[Quartile]

I apologize for posting here. My mind is too open and my ideas make more philosophical sense than they do physical sense. Whoever thickened the line between the two was a moron and an asshole.

[Klaynos]

You also have the problem that for a star you have to have a hydrogen burning stage and the earth is just not massive enough to hold hydrogen in a gaseous form it just floats away....

[Edtharan]

I apologize for posting here. My mind is too open and my ideas make more philosophical sense than they do physical sense.

If someone is genuinly interested in the answer, then the is no such thing as a bad question. An inquiering mind needs to be open, but with that you need to have the ability to critically analyse what you encounter.

 

I find it funny (not in a good way) that those that are trying to convince you of their beliefs, calim that scientists have colsed minds and that to accept their beliefs you must have an open mind. It is usually the other way around, the scientists are willing to question and accept many more things, but only so, long as it stand up to critical analysis. Where as the one trying to convinse you of their beliefs have closed their minds to any other posibility, even that they might be wrong.

 

The fact that you are willing to ask these questions and to investigate answers means you have an open mind.

 

The fact that you don't just accept the first plausable sounding answer that you encounter means that you are willing to accept critical analysis.

 

What you are doing is exactly right. There is no need for an apology because your post was perfectly in line with what this site stands for: Scientific Knowledge (and learning). Keep it up.

[Quartile]

I posted this topic because I recently came across stellar evolution. The fact that things in space are involved in such long-durations of change is, to me, groundbreaking physical evidence that there is an underlying process at play in the universe.

 

You also have the problem that for a star you have to have a hydrogen burning stage and the earth is just not massive enough to hold hydrogen in a gaseous form it just floats away....

 

A white dwarf is not massive enough to have a hydrogen burning stage either, will you debate with me whether or not a white dwarf could have once been involved in hydrogen fusion? What is the process by which a star grows and decays? Do human beings really know, or have we fudged the math this way and that in order to get an answer that stops people from questioning?

[Klaynos]

A white dwarf is not massive enough to have a hydrogen burning stage either, will you debate with me whether or not a white dwarf could have once been involved in hydrogen fusion? What is the process by which a star grows and decays? Do human beings really know, or have we fudged the math this way and that in order to get an answer that stops people from questioning?

 

I'm actually quite well versed in stellar evolution now. And we know ALOT about formation, but even more about stellar death, and MASSIVE amounts about main sequence life.

 

Now let's take a look at white dwarfs...

 

Consider a 5 solar mass star, it'll have an inert CO core, with 2 active shells around it (one of helium and one of hydrogen), the envelope will expand as the core shrinks, and it'll become a red giant with unstable helium burning, this makes the star pulse and as a result of this the envelope is pushed away, and creates a planetary nebula, we've got LOADS of evidence for them because they glow as circles in the sky, rather cool! At this point you have a super dense hot star surrounded by the quickly escaping nebulae, the nebula glows because of the radiation hitting it from the star (the white dwarf) and we can do spectral anaysis of this and compare it to our models and by george they match!

 

I could spend alot of time discussing the maths for you, but it'd probably be more useful for you if you found it in a book, I'd recomend: D. Prialnik, an introduction to the theory of stellar structure and ecolution, CUP, sections 8.7 and 8.8

[Edtharan]

Do human beings really know, or have we fudged the math this way and that in order to get an answer that stops people from questioning?

Good question (I like how you keep questioning).

 

We know how atoms act during fusion, and this tells us how atoms in stars behave. We can check this through several methods, the main ones are through the spectral lines of a Star.

 

Spectral lines are dark lines that show up in the light from stars when you pass it through a difraction grating. It is like with a prisim how it splits the light up. The spectral lines are caused as certain elements in the atmosphere of stars absorb certain frequencies of light and when you split the light up line that you can see them.

 

Other methods used to work out what is happening in a star is through the star's mass, colour and size. Using these (and a few other observations) we can test our theories as to what is happening within a star. If the model maches the observed data we can say that the model is describing the processes that occure within the star.

 

This means we can extrapolate what we know from experiments here on Earth and check to see if the Stars behaves the same way.

 

Because wew can work out what the processes are that are going on inside a Star this way, we can then use that model to work out what will happen to a star over it's life time.

 

We can check this too as we can see many stars and some are younger and some are older, and although there seems to be a lot of difference between them, they have enough similarities for us to check the models and that we got the life history of the star worked out correctly.

 

The fact that things in space are involved in such long-durations of change is, to me, groundbreaking physical evidence that there is an underlying process at play in the universe.

Only from our perspective is it long duration. In the perspective of the time span of the universe, steller evolution is quite rapid. In the perspective of a Mayfly, our lives are a long duration process.

 

I don't really think it does provide any evidence that there is some underlying process at work (there might be or their might not be, but this doesn't really provide proof of it).

 

Stellar evolution is just a battle between two forces: Gravity and Heat. What we call a Star is just a place where they balance each other out (and Heat will loose in the end ).

[Klaynos]

Some stellar evolution processes take only are quite quick (like the wd losing it's envelope, the unstable process has a period of 100 years)... of course the kelvin-helholtz timescale is on order of 10^7 years.

[Pangloss]

Quartile has been issued an infraction for trolling for creating this thread with dishonest intentions and then insulting people who tried to help him. I'll leave the thread here because it's a good discussion and an excellent effort by our community to answer what at least initially appeared to be an honest question.