Re: Question about radiation pressure

<curiosus_2008@xxxxxxxxx> wrote in message news:a0750616-35f2-41ca-9901-58bff6281d87@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Question about radiation pressure


We know several examples where radiation pressure is overcoming
gravity: for example the tail of comets or the formation of solar
systems.

The main reason is that the effect of radiation pressure increases
when the size of the particles decreases.


But not when the particle is a single atom or ion. Radiation pressure affects tiny dust particles much more than it affects atoms or ions. Atoms are not nearly so strongly affected, relative to gravity. However, ions are picked up by the solar wind and transported. Thus a typical comet has two tails, a dust tail pushed out by radiation pressure and a gas tail of ions carried by the solar wind.

A current leading theory to explain the chemically peculiar Lambda Bootis stars involves accretion of gas from denser clouds of the interstellar medium. Radiation pressure on gas atoms and ions is small compared to gravity.

For example radiation pressure from the Sun is stronger than gravity
for atoms of hydrogen. It is even enforced for dust grains of a

Gravity is much stronger that rad pressure for atoms, but the solar wind prevents hydrogen gas from being accreted.

particular size.

If that is true in the vicinity of the Sun, that is still true 2
MegaParsecs away, as both radiation pressure and gravity propagate as
1/d^2.

So stars are not attracting atoms and dust, but repel these.

Stars tend to repel dust but can attract gas gravitationally.


According to current estimations, a large part of the mass of galaxies
is made of hydrogen and dust.

Now consider the effect of radiation pressure from one galaxy to
another galaxy: if an important part of the galaxy is made of
hydrogen, an important part of that action should be repulsion and not
attraction.

So my question is:

If there is an important repulsion exerted on hydrogen and if hydrogen
is prevalent, is it possible to consider that hydrogen is repelled,
and is then attracting the stars of the galaxy by gravitation?

Eventually, depending on the proportion of hydrogen, it could occur
that a galaxy repels another galaxy and does not attract it, or
attracts it less than expected.

--
Curiosus
http://www.geocities.com/curiosus_2008/



--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

.

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