In intergalactic HII regions, the hydrogen atoms are ionized by
ultraviolet radiation, not gravitational interactions. The
ionizing UV is usually emitted in nearby galaxies.
Note: Astronomers indicate the ionization state of atoms via
roman numerals: I indicates a neutral atom; II indicates an ion
with a charge of +e; III indicates an ion with a charge of +2e;
etc.
Daniel Crowe
Oklahoma School of Science and Mathematics
Ardmore Regional Center
dcrowe@sotc.org
-----Original Message-----
From: Leigh Palmer [mailto:palmer@SFU.CA]
Sent: Friday, November 21, 2003 2:06 AM
To: PHYS-L@lists.nau.edu
Subject: Re: Plasma
There was a mention of plasma in outer space. There is a considerable
mass of gas in intergalactic space that is nearly completely ionized.
Diffuse X-rays detected from rich clusters of galaxies show that they
often include gas (mostly hydrogen and helium) in that state. It is
thought that the ionization is due to gravitational interaction, that
the virial theorem applies for galaxies and ions alike. Of course this
process of virialization does not reach an equilibrium state in rich
clusters, but the high temperatures inferred cannot be accounted for by
any other process.