Magazine article Science News

Hubble Eyes the Cartwheel

Magazine article Science News

Hubble Eyes the Cartwheel

Article excerpt

Millions of years ago, a small, energetic galaxy plowed through the core of a large, quiescent one. Luckily for astronomers, this changed the dormant galaxy in dramatic fashion.

Like a pebble cast into a pond, the tiny intruder generated a ripple of energy that expanded outward from the center of the big galaxy. Traveling at about 320,000 kilometers per hour, the wave compressed gas and dust in front of it and ignited rings of star birth in its wake. This process has so far lasted for some 200 million years. At the forefront of the wave lies the bluest, newest batch of stars; closer to the core reside redder, older stars.

That's how astronomers believe the Cartwheel, a striking, ring-shaped galaxy complete with spokes and a brilliant, bulls-eye core, got its shape (SN: 4/18/92, p.248). Images recently taken by the Hubble Space Telescope depict with unprecedented clarity the Cartwheel's highly organized structure. The pictures also provide new clues to what the Cartwheel, located 500 million light-years from Earth, may have looked like before the fateful collision.

Hubble's pictures reveal hundreds of bright blue knots -- individual clusters of newborn stars -- that the expanding wave generated. Huge loops and bubbles indicate where massive stars, also formed in the aftermath of the collision, exploded as supernovas, hurling their contents into space. In addition, the images show in new detail the galaxy's true colors -- its red center and blue outskirts -- notes Kirk D. …

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