A new theory of how galactic spiral arms work simulated

Since the 1960's we've been told that the spiral arms of galaxies are
just an optical illusion created by density waves of stars bunching up
or spreading out as they go from the crest to the trough. The stars that
make up the arms aren't actually travelling with the arms, and don't
actually belong to those arms. The arms and the stars are independent
features, like people doing the wave in a stadium. Most school children
would normally assume that the stars are travelling with those arms, so
this was explained to correct their assumption.

But it looks like the school children were right after all. The stars
are part of the arms, and they travel with the arms. The computer
simulation couldn't get the density wave theory to work. It turns out
that the stars are stuck to the arms through their mutual gravity. Some
stars move towards the inner part of the arms, while other stars move
towards the outer edges, but they stay with the arms all throughout.

Yousuf Khan

***

New theory of evolution for spiral galaxy arms
""We have found it impossible to reproduce the traditional theory, but
stars move with the spiral pattern in our simulations at the same speed.
We simulated the evolution of spiral arms for a galaxy with five million
stars over a period of 6 billion years. We found that stars are able to
migrate much more efficiently than anyone previously thought. The stars
are trapped and move along the arm by their gravitational influence, but
we think that eventually the arm breaks up due to the shear forces,"
said Grand."
http://www.sciencedaily.com/releases...0420111343.htm