Cartwheel Galaxy — Located 500 million light-years away in the constellation Sculptor, the Cartwheel Galaxy looks like a wagon wheel. The galaxy’s nucleus is the bright object in the center of the image; the spoke-like structures are wisps of material connecting the nucleus to the outer ring of young stars.
This close-up image of the galaxy’s nucleus reveals the comet-like knots of gas. These knots are mostly confined to the core’s left side and appear as white streaks inside the blue ring.
The “heads” are a few hundred light-years across; the tails are more than 1,000 light-years long, the longest of which is nearly 5,000 light-years. The structures look like comets because they probably were spawned by a collision between high-speed and slower-moving material. This collision created an arrowhead-shaped pattern called a bow shock, which is similar to the wake of a boat speeding across a lake.
The galaxy’s unusual configuration was created by a nearly head-on collision with a smaller galaxy about 200 million years ago. The Cartwheel Galaxy presumably was a normal spiral galaxy like our Milky Way before the collision.
This spiral structure is beginning to re-emerge, as seen in the faint arms or spokes between the outer ring and bulls-eye shaped nucleus. The ring contains at least several billion new stars that would not normally have been created in such a short time span and is so large (150,000 light-years across) our entire Milky Way Galaxy would fit inside.
Image Credit: Curt Struck and Philip Appleton (Iowa State University), Kirk Borne (Hughes STX Corporation), and Ray Lucas (Space Telescope Science Institute), and nasa.gov”> NASA