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lunes, 8 de junio de 2009

Scientists Make Explosive Discovery About Nature Of Supernovae

North Carolina State University astrophysicists have answered a long-standing question about the nature of one of our galaxy’s most famous supernova explosions, discovering a new class of supernova in the process.
Dr. Stephen Reynolds, astrophysicist in NC State’s College of Physical and Mathematical Sciences, along with colleague Dr. Kazik Borkowski and a team of scientists from NASA, Rutgers University, and the Naval Research Laboratories, set out to determine whether the Kepler supernova, which occurred in 1604 A.D., was a core collapse supernova or a thermonuclear supernova.

They revealed their results in a press conference today at the annual meeting of the American Astronomical Society.

A core collapse supernova occurs when a single, massive star (with a mass eight times greater – or more – than that of our sun) reaches the end of its life and explodes. Core collapse supernovae leave pulsars, rapidly spinning neutron stars, behind when they occur. They also tend to be surrounded by circumstellar medium – leftover elements from the star that collapsed, as well as large amounts of oxygen and small amounts of iron. These supernovae are usually located near “star-forming” sites along a galaxy’s edge.

Thermonuclear, or Type Ia, supernovae occur when a white dwarf star, which typically travels through space with a companion star that eventually “leaks” its own mass onto the dwarf, reaches its mass limit and explodes. These supernovae can be found all over a galaxy, are typically not associated with any circumstellar medium, and produce large amounts of iron.

The Kepler supernova has long puzzled scientists because it has features that are common to both types of supernova: The Kepler supernova’s location and the presence of a lot of iron are indicative of a Type Ia supernova, but the dense surroundings and nitrogen-enriched circumstellar medium are commonly associated with the aftermath of a core collapse.

Reynolds and his team used the powerful Chandra X-ray telescope to observe the Kepler supernova, and they discovered that Kepler is something entirely new: a Type Ia supernova in which the progenitor of the white dwarf star that created it had enough mass to create circumstellar medium.

“We really don’t know much about Type Ia supernovae, and they’re really important to our understanding of the universe,” Reynolds says. “We use the fact that they all have similar luminosities, or brightness, to calculate the distance of galaxies and to determine how much and how quickly the universe is expanding.

“Type Ia’s are also the source of the majority of iron in the universe, and can give us a lot of information about its chemical history. A new class of Type Ia supernova will have huge implications for our ability to understand the source of the elements that create our universe.”

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