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Sol's Journey!

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Wade Hampton III

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Sol's Journey!

PostSun Sep 02, 2018 7:20 pm

Our motion through space isn't a vortex,
but something far more interesting...
Out There
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Wade Hampton III

  • Posts: 1543
  • Joined: Fri Oct 18, 2013 10:40 pm
  • Location: Pontiac, SC

Re: Sol's Journey!

PostMon Sep 24, 2018 2:25 am

Landing On A Future Sun?

Jason Tiscione, Software Engineer, asks....

Quadrillions of years from now, when the Sun has faded to a white dwarf
then black dwarf and eventually cooled completely, would we be able to
land on its surface? What would it consist of?

A white dwarf is an object structured like an atom with discrete, filled
electron orbitals, but rather than a nucleus, it has a cloud of free
protons flying around and still behaving classically, seemingly unaware
of the weird situation. The bigger, puffier electrons are not behaving
this way - they’re stacked up with no room to spare, like the electrons
in a large neutral atom. The star can’t collapse because it’s held up by
electron degeneracy pressure - if you squeeze the star, you’re squeezing
these filled electron orbitals too, making them smaller, so that the
electrons need more energy to occupy them. That extra energy must come
from you squeezing. (Ordinary individual atoms are hard to “squeeze” for
the same reason.) The heavy protons in the star would love to collapse
further, maybe to the size of a city, but the electrons won’t accompany
them down. The weight of the protons is counterbalanced by electron
degeneracy pressure only at a certain radius, and if the mass increases,
this equilibrium radius decreases. The star will actually shrink if it
gets heavier.
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Electron degeneracy pressure is fundamentally different than what currently
exists in the sun. Its core has a density ten times larger than solid lead,
but gravity is still countered with ordinary PV=nRT pressure. (It’s weird,
but the ideal gas law you learn in high school still works in the Sun’s core.
It’s so hot down there that the energetic particles have deBroglie wavelengths
that are small even compared to the minuscule mean free path of a particle in
such a dense material.) In a white dwarf, the core density is 100,000 times
that of solid lead. You can’t use PV=nRT anymore- the mean free paths are
too short for classical physics. Degeneracy pressure doesn’t have a thermal
origin; it’s a quantum effect. It persists even at a temperature of zero
once the star enters its dark era.
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(If the temperature and density are high enough, the electrons with the
highest energies can engage in the uphill p + e => n + neutrino reaction.
The neutrinos leave, the neutrons sink, their gravity squeezes the star,
electron orbitals get tighter, their energy rises, more neutrons form and
fall to the center, and you get what a stellar climatologist would call a
“positive feedback loop”. This is an oversimplification, since there are
similar uphill reactions involving carbon and oxygen that require less
energy, and these are what provide the actual ignition. The supernova
starts as a scattered flash deflagration in the core that spreads outward,
in a process known as carbon detonation that triggers all Type Ia supernovas.)

The star’s temperature is extremely high, so there are a large number of
unfilled electron orbitals. As the “atom” relaxes to its ground state over
trillions of years, electrons in higher energy states fall into these
unoccupied orbitals and the star emits photons. The surface is extremely
hot and bright, and most of the radiation is UV and soft X-rays rather
than visible light. If a white dwarf had the sun’s angular radius in the
sky, you would be less impressed than vaporized. Radiative cooling obviously
proceeds really slowly because the star only has the surface area of the
Earth to shine with now. Once the parking lot of electrons is completely
full, the star is in thermodynamic equilibrium with the rest of the universe
and goes dark.

Then you land on it, which means you’re an idiot, because the surface gravity
is about 400000 g. Instantly the electrons in your body hit the star and
occupy the lowest energy unoccupied orbitals they can find on the surface.
The protons in your body sink into the star with them, and since they are
heavier, they impart most of the energy of the collision and kick up some
electrons into unoccupied higher energy orbitals. The star shrinks a tiny
bit and may glow for little while near your landing site. And there’s a
very slight chance, on a star a bit heavier than the sun, that you have
made the thing heavy enough for the highest-energy electrons to initiate
an explosion which will not just hurt you but others around you. So don’t
do it.

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