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> Cartwheel galaxy
Cartwheel galaxy
author: Anglo-Australian Observatory/David Malin Images/Novapix
reference: a-gax95-00041
Image Size 300 DPI: 9 * 9 cm
This diminutive group of galaxies appears small because it is distant, about 500 million light years away. But here, a dramatic collision between two members of a small group has transformed one of them into a brilliant ring of stars, connected to the bright nucleus by starry tendrils that are reminiscent of the spokes of a wheel. The Cartwheel itself was a galaxy about as big as the Milky Way probably with much the same spiral structure. However, one of the small companion galaxies has recently passed through its center. This is perfectly possible -- the stars are so far apart that collisions are rare. But the intruder intercepted the galaxy almost at right angles to the disk and it passed through the gravitational hub of the galaxy, the bright nucleus. The gravitational pulse of the interaction sent a ripple of energy through the galaxy disk, triggering a violent wave of star formation which has spread as far as the visible outer rim. the youth of this feature is evident from its color, which is the pale blue of young stars.
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