Explanation:
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 400 million
light years away in the
constellation
Sculptor
(two smaller galaxies in the group are visible below and left).
Its rim is an immense ring-like structure over 100,000 light
years in diameter, composed of star forming regions filled with
extremely bright, massive stars.
When galaxies collide they
pass through
each other, their individual stars do not come into contact.
However, this ring-like shape is the result of
gravitational
disruption caused by a smaller galaxy
passing through a large one, compressing the interstellar gas and
dust and causing a star formation wave to move out
like a ripple across the surface of a pond.
This
false-color composite image of the
Cartwheel Galaxy is from space-based observatories.
The Chandra X-ray Observatory
data is in purple,
the Galaxy
Evolution Explorer ultraviolet view is in blue,
the Hubble Space Telescope
visible light picture is in green and
the Spitzer Space Telescope
infrared image is in red.
