Cartwheel of
Fortune
From NASA’s Astronomy Picture of the Day
By chance, a collision
of two galaxies has created a surprisingly recognizable shape on a cosmic
scale, The Cartwheel Galaxy.
The Cartwheel is part of
a group of galaxies about 500 million light years away in the constellation
Sculptor.
Two smaller galaxies in
the group are visible on the right.
The Cartwheel Galaxy's
rim is an immense ring-like structure 150,000 light years in
diameter composed of newly formed, extremely bright, massive stars.
When
galaxies collide they pass through each other, their individual
stars rarely coming into contact.
Still, the galaxies'
gravitational fields are seriously distorted by the collision.
In fact, the ring-like
shape is the result of the gravitational disruption caused by a small intruder
galaxy passing through a large one, compressing the interstellar gas and dust
and causing a a star formation wave to move out from the impact point like a
ripple across the surface of a pond.
In this case the large
galaxy may have originally been a spiral, not unlike our own
Milky Way, transformed into the wheel shape by the collision.
