How to shut down the Sun?

In article ,
Andrew Usher writes:
In a low-mass red dwarf, one might have central density =
600 g/cc and T ~ 300 ev.

Where did you get those figures? That density seems way too high to
me, but I couldn't find any models below 0.8 solar masses in a brief
search. Central density is about 84 at 1 solar mass and about 76 at
0.8 solar masses according to the table in _Allen's Astrophysical
Quantities_ for zero-age main sequence. I'd expect the central
density to decrease down to the hydrogen-burning limit because the
central temperature can't change much, and the pressure has to go
down (less mass to support).

At those conditions, the degeneracy pressure
is 2.6e11 bar and the gas pressure 1.3e11 bar, for a 'degeneracy
index' of 2. I would say both would need to be considered.

I haven't checked your figures but don't doubt your calculation. The
question is what stars and state of evolution, if any, these
conditions would apply to.

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Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Sorry about the late response, I lost track of this thread. Rely too
much on Google Groups to track my threads.

Andrew Usher wrote:
Yousuf Khan wrote:
The inward spiralling continued as gas flowed toward the white dwarf
primary. And the gas flow finally ended only once the secondary no
longer could maintain fusion in its core when it became a brown dwarf,
which is the stage they are at right now. They are relatively stable
now, but it won't last.

Why would that cause the gas flow to end? There is NO external
difference between the hottest brown dwarfs and the coolest red
dwarfs.

Anyways, getting back to this thread, the red dwarfs would have fusion
heat expanding their envelopes. So the red dwarfs would be much lower in
density and larger in volume and thus in diameter. As you said to Steve
Wilner elsewhere in this thread, the density of a brown dwarf resembles
dengenerate matter more than it does an ideal gas.

So basically a brown dwarf will be much smaller in diameter than a red
dwarf, and much more self-gravitating. Therefore an outside gravity
source would require closer proximity to break it apart.

The next stage will see further spiralling inward of the two bodies due
to relativistic frame dragging friction between them, as they orbit
around each other and lose energy through gravity waves.

Yes, and they eventually will merge in a big nova (not a Type Ia
supernova - not enough added mass).

Agree there.


Yousuf Khan