Michael Dines wrote:

And, since black holes aren't in an atmosphere there's no audio waves.
And because of their gravity light waves can't escape - so how do they
propagate this hum?

I'm going to take this up on sci.physics to be sure but I
don't believe this is a sound wave. It may be the relic or
fossil of one but I am pretty sure that the density of
intergalactic gas (and this is intergalactic, not
interstellar) is insufficient for there to be anything like
an acoustic pressure or the pressure differential which is
necessasary for there to be an acoustic wave. The molecules
there are at the level of one (or thereabouts) per cubic
meter, IIRC, and at that distance from each other they just
couldn't exert the mutual electrostatic repulsion and
interaction that causes pressure. OTOH, if they were ions
rather than molecules I suppose it could be possible.

I'll bet it is just density striations that are propegating
inertially away from whatever gave them that inertia rather
than true acoustic waves. They could possibly be a frozen
sound field from a time when the medium was dense enough to
support sound but intuition tells me that such a wave would
have damped out first rather than being frozen.


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein