7. What's making these gamma rays?
A car crash of cosmic proportions -- this cartwheel galaxy, imaged in 1994, shows that space is no peaceful place. Years back, the galaxy in the center of the wheel was apparently smacked by another galaxy -- perhaps the villain is lurking at the right? The whack sent a ripple of energy, shown by the wheel, into space, and it's now expanding faster than Dale Earnhardt, Jr. on the straightaway -- about 200,000 miles per hour. The energy wave is causing a spasm of star formation, shown by the bluish-white clumps at the edge of the donut, and thousands of supernova explosions.
The cartwheel, 150,000 light years across, is now larger than our Milky Way galaxy, and may eventually return to its presumed earlier status as a spiral galaxy (note the gauzy arms connecting the core to the ring).
Which party performed this hit-and-run? Either of the smaller galaxies at right looks guilty: The lower-right galaxy is bent, spindled and mutilated, with lots of new star formation, while the upper right galaxy has lost its gas -- which may have been stripped out during the collision.
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