An N.C. State University astrophysicist has a new explanation for why remnants of some dying stars spin. The theory is published today in the journal Nature. If it's accepted by astronomers, college textbooks will require updating.

WHAT'S UP? Since the 1960s, astrophysicists have been aware of neutron stars, the remains of giant stars that collapsed after running low on fuel. The objects are so dense that one teaspoonful of neutron star matter on Earth would weigh a billion tons, NASA has calculated. Pulsars are neutron stars that spin -- 20 or more times each second. Many scientists think pulsars spin because the stars that spawned them spun, too.

WHAT'S NEW? John M. Blondin of NCSU and Anthony Mezzacappa of Oak Ridge National Laboratory in Tennessee ran mathematical models on a federal supercomputer at Oak Ridge to better understand the explosions that create pulsars. The models showed something unexpected. Explosions produced forces swirling in just the right way to make a pulsar turn.

WHY NOW? Blondin and his partner were able to produce three-dimensional models of supernova explosions using the supercomputer, one of the fastest devices in the world, and imaging software produced by Apex-based Computational Engineering Inc. Most previous studies were confined to two dimensions and did not capture the forces Blondin's group observed.

WHO CARES? Amateur and professional astronomers for sure. Pulsars are far from Earth. Scientists study them remotely, with telescopes and computer models. Any insight into their basic workings gives a more accurate view of the universe, said UNC-Chapel Hill astrophysicist Chris Clemens. "If we can't answer the simple questions, more complex questions are going to elude us," Clemens said.