Hubble Eyes Galaxy as Flat as a Pancake
Located
some 25 million light-years away, this new Hubble image shows spiral
galaxy ESO 373-8. Together with at least seven of its galactic
neighbors, this galaxy is a member of the NGC 2997 group. We see it
side-on as a thin, glittering streak across the sky, with all its
contents neatly aligned in the same plane.
We see so many galaxies like this — flat, stretched-out pancakes —
that our brains barely process their shape. But let us stop and ask: Why
are galaxies stretched out and aligned like this?
Try spinning around in your chair with your legs and arms out.
Slowly pull your legs and arms inwards, and tuck them in against your
body. Notice anything? You should have started spinning faster. This
effect is due to conservation of angular momentum, and it’s true for
galaxies, too.
This galaxy began life as a humungous ball of slowly rotating gas.
Collapsing in upon itself, it spun faster and faster until, like pizza
dough spinning and stretching in the air, a disc started to form.
Anything that bobbed up and down through this disk was pulled back in
line with this motion, creating a streamlined shape.
Angular momentum is always conserved — from a spinning galactic disk
25 million light-years away from us, to any astronomer, or
astronomer-wannabe, spinning in an office chair.
