Lopsided Supernova Blasts Uncovered

Cassiopeia A
The mystery of how Cassiopeia A exploded is unraveling. Credit: NASA/JPL-Caltech/CXC/SAO

Some jumbo stars commit stellar suicide in surprisingly lumpy explosions, according to a new study in Nature.

Scientists led by Caltech’s Brian Grefenstette looked at Cassiopeia A, a supernova that first appeared in nighttime skies around the year 1670. The supernova’s wispy remnants rest some 11,000 light-years away from Earth, stretched across some 59 trillion miles (95 trillion kilometers) of sky in the constellation Cassiopeia.

Astronomers had long suspected that supernova stars similar to Cassiopeia A, which start out weighing more than eight times as much as the sun, end their lives in asymmetrical explosions. (See more supernovae pictures.)

Traces of radioactive titanium observed in the clouds of Cassiopeia A indeed show that an unequal distribution of the metal was blasted out of the star in the final collapse of its core.

The findings, made with NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), confirms a theory of lopsided supernova explosions.

But they also raise a new mystery, says astrophysicist J. Martin Laming of the Naval Research Laboratory in Washington, D.C., writing in a commentary accompanying the study.

Rather than spewing out heavy metals such as titanium and iron in similar lopsided ways, as the unbalanced-supernova-explosion theories would suggest, the dying star appears to have shot them into space in unrelated directions. (Also see “Newfound Monster Supernova Breaks Records.”)

“Where does this leave us?” Laming writes. Confused as ever, he concludes.

One theory is that Cassiopeia A became an exotic “quark” star after it exploded. The transformation might have led to a second series of explosions that scrambled the direction of the supernova’s death throes. Only more observations from NuSTAR and NASA’s Spitzer infrared space telescope can help solve the new mystery, he adds.

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