Re: Heavy Protons & Life Without Hydrogen

On Jul 25, 1:52 pm, "Logan Kearsley" <chrono.sur...@xxxxxxxxxxx>
wrote:
"Luke Campbell" <lwc...@xxxxxxxxx> wrote in message

Okay, so back to the original question - you have a gas of deuterium,
3He and 4He. Over time, this will radiate away heat and contract
under its gravity, breaking up into contracting clumps that form star
systems. As the collapse continues, the temperature at the center of
the stars will increase to the point where deuterium starts to fuse.

Since deuterium fusion is a lot easier than protium fusion, though, without
any protium around to dilute it, it seems to me that you'd end up with a lot
of objects that would have ended up as brown dwarfs / super-jupiters in our
universe turning into very small red dwarf (infrared dwarf?) stars.

This sounds about right.

The D-D and D-3He reaction rate is much higher than the p-p reaction
rate. This will have a profound impact on the stellar structure - at
a guess, I'd say the stars will be cooler and have a larger volume for
a given total mass, but I don't know whether the star would be putting

Because the reaction would start up earlier, and keep the protostar from
collapsing as much?

Yup.

This continues until the D and 3He are used
up. Then the star contracts into a red giant and burns its 4He to
carbon, just like in our universe. The end state of these 4He burning
stars is familiar to all of us - either going out in a bang and
leaving a neutron star, or going out with a whimper and leaving a
white dwarf (which could then accrete enough additional material or
collide with another white dwarf to also go out with a bang).

Would neutron stars still turn out the same? I would expect, if something
more exotic doesn't happen, at least neutron stars would tend to be hotter
due to the release of energy as protons convert into neutrons. Unless the
high pressure stabilizes them, like it stabilizes neutrons in our universe,
in which case you end up with 'neutron stars' that are composed of
neutron-proton-electron plasma, which I presume would be less dense. Would
that have any particularly weird effects?

Neutron stars would be essentially the same. You don't get neutron-
proton-electron plasma for the same reason as in our universe, at very
high electron degeneracy pressures you get the reaction e+p -> n+nu.

What you should worry about is the deuteron binding energy. This
tells you how much energy will be released upon neutron fusion. If
this is very low, you not only get less heat, you get equilibrium
between the reactions
n+n -> D+e+nu_bar
D+e -> n+n+nu
The second reaction not only absorbs energy, but the combination of
the two will cool the cloud by neutrino radiation. This could keep
the clouds quite cold.

Which *would* allow them to collapse, yes?

Yup.

Resulting in neutron-fusion stars
that initially release a lot of neutrino radiation, which slowly starts
emitting electromagnetic radiation and expanding as deuterons/tritons (maybe
some heavier nuclei, since a neutron rich environment would be conducive to
adding on more and more neutrons?) build up, then expands and increases in
electromagnetic luminosity when deutrium burning starts? And they would be
much dimmer per unit mass than stars are in our universe, due to the
combination of less energy from fusion, and lots more energy being lost to
neutrinos.

There is the complication that as the temperature (measured in kinetic
energy per degree of freedom) increases past the binding energy you
tend to get the back reaction occurring about as often as the forward
reaction, which absorbs heat. As a consequence, you will never raise
the temperature much above the binding energy. You would end up with
cold, degenerate spheres of heavy hydrogen and possibly helium after
the neutron cloud radiated away all of its energy via neutrinos. At
these degenerate densities, you could get a runaway fusion reaction,
resulting in a supernova as the entire degenerate star fuses
suddenly. As a comparison, in real life the temperature required for
fusion is about two orders of magnitude lower than the binding energy
of a deuteron, so we don't get this phenomenon.

How would one go about figuring out the reaction rates, given binding energy
/ mass ratios / whatever else is relevant? (And doesn't binding energy have
something to do with the mass ratios?)

This gets complicated. You need to know not only the binding energy
but also the reaction barrier. Probably, what you need to do is run a
lattice QCD calculation on your configuration to get the answer. This
means you need access to a supercomputer.

Luke

.

Relevant Pages

  • Re: The Dangerous Liberty of Engineering vs. Lukewarm Dominionism
    ... version of massfree energy into kinetic energy, ... AND EARTH ZPE RADIATION. ... WITH THE EXCEPTION THAT NUCLEAR AND ELECTRON ... Galactic thick disk discoveries indicate stars with low ...
    (sci.space.policy)
  • Re: Heavy Protons & Life Without Hydrogen
    ... Luminous nebulas instead of stars would be cool. ... Note that the reaction product of neutron fusion is a charged ... A small enough energy output from fusion ought to prevent stars/planets ...
    (rec.arts.sf.science)
  • Re: Gravity and electricity
    ... That's energy out. ... sun has been happily pumping out sunshine that entire time. ... A big part of the energy flowing away from stars is ... in the form of electromagnetic radiation. ...
    (sci.physics)
  • Re: Heavy Protons & Life Without Hydrogen
    ... Luminous nebulas instead of stars would be cool. ... Note that the reaction product of neutron fusion is a charged ... out more or less energy (I have a slight tendency to say less energy, ...
    (rec.arts.sf.science)
  • Re: The first Day The Earth Stood Still
    ... directors and writers explaining the differences ... between asteroids, planets, comets, stars, galaxies and universes. ... converting matter into energy. ...
    (rec.arts.sf.movies)
Loading