Why Do We See Spiral Arms in Some Galaxies?

[xtmartx]

i heard a theory that spiral galaxies might have been shaped that way by electrical charges and magnetic fields. but who knows

[RexNunc]

i love the universe so very much

[crubs83]

if galaxies were billions of years old, then these spiral arms should not be recognisable

[SpitzerJim]

Yes, actually they would, because spiral arms are inherently *new* features which are continually changing and evolving as galaxies age. We find that younger galaxies generally do *not* have spiral arms yet.

[Tigerbaseball1]

how fast do these gravity waves travel?

[CohanDigitmatta]

how long is a peice of string?

[SpitzerJim]

The speed of the density wave really depends on the specifics of the galaxy. That's like asking "How fast does a traffic jam move?" The answer is "slower than the rest of the freeway" but we'd call it a traffic jam regardless of whether the cars were averaging 35 mph or 5 mph.

[joshscott911]

why is Olympus Mons so big?