Remains of 140-Year-Old Supernova Discovered

First of many young supernova remnants?

X-ray (NASA/CXC/NCSU/S.Reynolds et al.); Radio (NSF/NRAO/VLA/Cambridge/D.Green et al.)

Astronomers have discovered traces of a star that went supernova about 140 years ago as viewed from Earth*, around the time of the U.S. Civil War and the publication of Charles Darwin's The Origin of Species. The expanding debris cloud, or remnant, known as G1.9+0.3, lies near the center of the Milky Way, about 25,000 light-years from Earth.

Besides making G1.9+0.3 the youngest supernova remnant known in our galaxy, the finding begins to fill a peculiar astronomical gap. Based on studies of other galaxies, researchers estimate that about three supernovae should pop off per century in the Milky Way. They knew of one recent remnant, Cassiopeia A, which went supernova around 1680 by Earth's watch.

Researchers first identified G1.9+0.3 as a supernova remnant in 1985, using the National Science Foundation's Very Large Array (VLA), a sprawling network of radio telescopes in Soccoro, N.M. They estimated its age at 400 to 1,000 years old, Earth-time.

More than 20 years later, in 2007, a team observing the remnant via NASA's orbiting Chandra X-Ray Observatory found that it had grown by a surprising 16 percent, implying that the object was younger than they thought. When researchers checked double-checked using VLA, they got the same result, published in twin papers in The Astrophysical Journal Letters and Monthly Notices of the Royal Astronomical Society.

Despite the supernova's timing, contemporaries of Lincoln and Darwin would have missed it, because dust and gas surrounding the dying star would have blocked the flash of visible light. The expanding gas cloud shines brightly, however, in radio and x-ray frequencies.

G1.9+0.3 may be the tip of the iceberg. "If the supernova rate estimates are correct, there should be the remnants of about 10 supernova explosions in the Milky Way that are younger than Cassiopeia A," said David Green of the University of Cambridge in England, leader of the VLA study, in a statement. "It's great to finally track one of them down."

*Clarification (5/15/08): The supernova marked by G1.9+0.3 would have occurred 25,000 years ago, but because of its distance from Earth, the supernova's light would have first become visible 140 years ago.

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