Supersonic Comet-Like Objects (right) in Heart of the Cartwheel Galaxy (left)

Researchers analyzing the Hubble Space Telescope's dramatic pictures of the Cartwheel galaxy have discovered immense comet-like clouds of gas speeding through the heart of the galaxy at nearly 700,000 mph.

Located 500 million light-years away in the constellation Sculptor, the 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. The galaxy's unusual configuration was created by a nearly head-on collision with a smaller galaxy about 200 million years ago.

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.