Photo in the News: Star Explosion Highlights "Purple Rose of Virgo"

Purple rose and supernova photo
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March 29, 2007—Lightning may never strike twice in the same place, but star explosions apparently can.

For the second time in 11 years, the galaxy known as NGC 5584 is garnering attention as the brightly colored home of a brilliant supernova.

Located about 75 million light-years away in the direction of the constellation Virgo, NGC 5584 is slightly smaller but similar in shape to our own galaxy, the Milky Way. Scientists suspect that, like the Milky Way, the "purple rose" galaxy houses an energetic and supermassive black hole at its center.

Now that center is being outshined by SN 2007af, the brightest supernova seen so far the year. Visible as a white dot below and to the right of NGC 5584's center, the explosion was detected on March 1 by the European Southern Observatory's Very Large Telescope.

Supernovas of this kind—called Type 1a—usually occur in binary systems, when a compact star called a white dwarf draws matter away from its companion. When it gains enough mass, the white dwarf collapses under the pressure—setting off a cosmic fireworks show and sending matter hurtling off in excess of 9,300 miles (15,000 kilometers) a second.

Type 1a supernovas are rare, but researchers know enough about them to use the explosions as cosmic yardsticks for measuring distance and studying the early expansion of the universe.

The explosion 11 years ago, however, was a much more puzzling type of supernova, and scientists remain baffled by what caused that explosion.

There may be more discoveries ahead for this busy galaxy, however. The luminous patches dotting NGC 5584's disk are stellar nurseries, where new stars are being formed at a prodigious rate, astronomers say.

—Aalok Mehta

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