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parallaxicality
2013-Nov-21, 01:03 PM
Could someone help me decipher this paper (http://www.jstor.org/stable/10.1086/319535)?

It's somehow related to this graph (http://www.jstor.org/action/showPopup?citid=citart1&id=fg2&doi=10.1086%2F319535), and the paper suggests that the black dwarf state occurs near the end of the sequence.

All I want to know is how long it will take for the Sun to become a black hole?

Noclevername
2013-Nov-21, 01:05 PM
Could someone help me decipher this paper (http://www.jstor.org/stable/10.1086/319535)?

It's somehow related to this graph (http://www.jstor.org/action/showPopup?citid=citart1&id=fg2&doi=10.1086%2F319535), and the paper suggests that the black dwarf state occurs near the end of the sequence.

All I want to know is how long it will take for the Sun to become a black hole?
Never, it lacks the mass to become a black hole. A black dwarf is a white dwarf that has lost all its heat; the universe is not currently old enough for that to have ever happened anywhere yet .

Noclevername
2013-Nov-21, 01:06 PM
http://en.wikipedia.org/wiki/Black_dwarf


Because the far-future evolution of white dwarfs depends on physical questions, such as the nature of dark matter and the possibility and rate of proton decay, which are poorly understood, it is not known precisely how long it will take white dwarfs to cool to blackness.

So not yet known.

parallaxicality
2013-Nov-21, 01:45 PM
*bashes head against desk in humiliation*

You know how when you keep telling yourself, don't write something, don't write something, don't write something, and then you do? Well, yeah. That.

Ken G
2013-Nov-21, 02:25 PM
An interesting point, by the way, is that the distinction between a black dwarf and a black hole is basically whether or not a star has a quantum mechanical ground state that is allowed by its gravity. Lower-mass stars like the Sun do have such a quantum mechanical ground state (amazingly, a ground state for a whole star, like a single molecule the size of the Earth held together by gravity instead of electrostatic forces and containing some 1057 electrons), whereas higher-mass stars exert too much gravity to allow such a ground state to exist, and are thought to collapse into some kind of singularity (those that don't become neutron stars, which are a bit like a star that is a single atomic nucleus, though that analogy is stretched much more than the molecule analogy).

Noclevername
2013-Nov-21, 05:28 PM
You know how when you keep telling yourself, don't write something, don't write something, don't write something, and then you do? Well, yeah. That.

Oh, been there and done that so often the border guards know me on sight. :(

Amber Robot
2013-Nov-22, 06:22 PM
Lower-mass stars like the Sun do have such a quantum mechanical ground state (amazingly, a ground state for a whole star, like a single molecule the size of the Earth held together by gravity instead of electrostatic forces and containing some 1057 electrons)...

I've never heard of this before. Does it really make any sense to think of the Sun as having a quantum mechanical state? How would you even write the Hamiltonian for that?

Ken G
2013-Nov-25, 06:20 AM
I've never heard of this before. Does it really make any sense to think of the Sun as having a quantum mechanical state? How would you even write the Hamiltonian for that?The Hamiltonian is simple, we would generally just consider free particles in the overall gravitational potential of the entire ensemble (including the ions, which create the gravity but play little role in anything else except storing whatever small amount of heat is still in there). And yes, that has a ground state, which is calculated in the usual way-- you give each electron the minimum energy it can have and still generate enough pressure to withstand the gravity of the whole ensemble, while obeying the uncertainty principle and the Pauli exclusion principle. It turns out that is only possible if the total mass is below about 1.4 solar masses (though this depends a bit on composition, let's not worry about that). Since the Sun is below that, it does have a ground state, which we would call a black dwarf. More importantly, any state we would call a white dwarf is actually pretty close to that ground state in all regards except for how much light it is emitting, so we would generally use the approximation that it is in its ground state when we calculate the internal structure of a white dwarf, at least in the broad brush. Real models are a lot more complicated, as they have atmospheres and all that jazz.