View Full Version : Are Galaxies charged entities?

man from kibish
2008-Sep-21, 12:44 PM
In our small scale lives we experience electrically neutral objects where the number of protons equals the number of electrons. Is this also true for the heavenly bodies? Earth, Sun, Galaxy, Neutron star, Black hole?
Where can I read more about this subject?

yours truly,

Ken G
2008-Sep-21, 02:30 PM
Tiny net charges would be hard to notice. All we know for sure is that the charge must be pretty small, because its effects are negligible compared to gravity, and the gravity of individual particles is always vastly less than their electric forces when the particles have an elementary charge. You could probably have about one elementary net charge in each gram of material and not notice, but you couldn't have a lot more than that or we could tell.

2008-Sep-22, 01:58 AM
The basic arguments were set out in this paper (http://adsabs.harvard.edu/abs/1978ApJ...220..743B) by Bally and Harrison, which looks at the degree of gravitationally-induced charge separation that can happen on various scales before electrostatics brings things back toward neutrality. The abstract is short and to the point:

It is shown that all gravitationally bound systems - stars, galaxies, and clusters of galaxies - are positively charged and have a charge-to-mass ratio of the order of 100 coulombs per solar mass. The freely expanding intergalactic medium has a compensating negative charge. The immediate physical consequences of an electrically polarized universe are found to be extremely small.

Ken G
2008-Sep-22, 02:06 AM
That's interesting. Note that a coulomb is 6 x 1018 elementary charges, and a solar mass is 2 x 1033 grams, so 100 coulombs per solar mass comes out 3 x 10-12 elementary charges per gram. That creates a force on an electron that is 14 orders of magnitude less than gravity-- so I'm surprised that they can even put that much of a limit on the charge.

2008-Sep-22, 10:07 AM
To be charged... ' Any thing you say may be used against you in ...' :)
To be charged... ' A negative or positive imbalance in electric magnetic field radiation...'
A very weak force when measured against the forces of gravity and atomic force.
A very strong force when you look at coronal mass ejections from the sun...
Radio astronomy lives on this electro magnetic field activity and instability.

2008-Sep-22, 08:10 PM
Some may have an overall charge one way or the other, but since EM is limited in range compared to gravity, they're too far apart for it to make much difference. Even most individual stars in a single galaxy would have a hard time influencing each other magnetically unless they're in close binary (or more) orbits.

2008-Sep-22, 11:31 PM
Gravity is far far weaker than electricity.

However, on the scale of planets and stars and galaxies, that enormous amount of MASS adds up.
It greatly overwhelms the electric charge.
This is the main failure of the Electric Universe argument.