[Physics] Physics Digest, Vol 4, Issue 4

[carmam at tiscali.co.uk]

Carl, thank
you for your reply, and the link to one of your web pages was very informative,
and corrected a couple of mistaken beliefs of mine. The sun, as you say, is
traversing the spiral arm, but what I did not realise was that it would reverse
its journey (orbit) at the limb of the arm and go all the way back again – ad
infinitum. I thought that it would leave the spiral arm and pass into the far
less dense region between arms, then to catch up with the next arm. Your
article made complete sense. My other misconception was that I thought that the
sun was the only star to do this (silly me), but obviously the forces acting
upon the sun are the same forces acting on all the other stars. A very
informative article; well done.

Also I
always thought that the spiral arms were pointing retrograde, but you explained
why they are the shape that they are, and why they are pointing forward.

On now to
the “gravitational lensing” and the Einstein Cross. Visually, the four images
forming the cross are many parsecs from the central galaxy, and if these images
are formed by gravitational lensing, the central galaxy must be immensely
massive to be able to bend light at that distance and to such a degree. Such a
galaxy would have an extremely high rate of rotation or implode. This also
applies Abell 1689.

I am again
paraphrasing from Bernard Burchell’s excellent web site. We know that space is
not empty, it is a very tenuous gas with varying density, and as light moves
from one density to another, it will be refracted. As the density near a galaxy
(or galaxy cluster), will be more dense than in intergalactic space, then isn’t
it reasonable to assume that light bends due to refraction as it passes a
galaxy? This also explains the bending of starlight at the limb of our sun. The
sun’s corona is its atmosphere, and bends starlight, just the same as Earth’s
atmosphere does.

Going back
to the orientation of the spiral arms, I read this about M51

“The pattern was seen to gradually change along the length of
the Arm, with the objects tending to migrate together toward the wider
(forward) end of the pattern. ..”

The mention of the
wider (forward) end of the arm, reads as though the tip (narrow end) of the arm
is trailing, not leading. Could you clear this up for me please?

 

Tom.




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