Thursday, June 17, 2010

New Supernova Type Sheds Light on Universe's Origins

New Supernova Type Sheds Light on Universe's Origins By: R. Colin Johnson

Scientists have discovered a third type of supernova that could explain the universe’s previously puzzling abundance of calcium—which enabled the evolution of life—as well as eliminate at least one reason to hypothesize the existence of dark matter.

Standard astronomical theory maintains that all the elements heavier than hydrogen and helium were created and dispersed by supernovae of two different types: hot, young giants that explode in a violent display and then collapse under their own weight; and very old, dense, white dwarves that explode in a thermonuclear explosion. Unfortunately, the universe as we know it has many more heavy elements—like the calcium that makes up your body—that cannot be accounted for by those two types of supernovae.

Now astronomers at the Weizmann Institute of Science (Israel) claim to have discovered a third type of supernova that could account for the abundance of calcium in the universe—as well as eliminate one reason to postulate "dark matter."

The new type of supernova first appeared in telescopes in 2005, but it took five years for the scientists to collect, analyze and explain the faint evidence from this odd sighting. By combining data from many different telescopes from around the world to determine its chemical makeup, the scientists now surmise that they are witnessing a new type of supernova.

The new supernova ejected too little material for it to be an exploding giant, and yet that material's chemical makeup did not match that of white dwarfs. Exploding white dwarfs eject mainly carbon and oxygen, but the new supernova had an abundance of calcium and titanium, which are usually produced in thermonuclear reactions involving helium.

A new type of supernova involves two stars: a donor and a thief. The latter (A) steals helium from its less massive, but larger, companion (B), which becomes hot and dense enough for a nuclear explosion (C) that releases calcium and titanium—the building blocks of life. It is unknown if the thief survives the explosion (D1) or collapses into a neutron star the size of a big city on Earth (D2). (Source: Dr. Avishay Gal-Yam, Weizmann Institute of Science)

To explain the odd behavior, the astronomers at the Weizmann Institute ran computer simulations in an attempt to deduce just what circumstances could have produced this unique supernova. By simulating different possible circumstances that could account for the presence of helium, the astronomers finally concluded that a pair of closely coupled white dwarves had to be involved. The unstable star stole helium from the donor during close passes until it reached a critical level, resulting in a fiery nuclear reaction.

Observations show that the main mass of the thief star was not consumed in the nuclear explosion, but the researchers as yet do not know its final fate, since the explosion could have triggered its compression and collapse into a neutron star—a dense, compact object the size of large city on Earth.

After sifting through historical records, the astronomers now believe that this donor/thief phenomenon may be common enough to explain other anomalies besides the abundance of calcium in the universe. In particular, dark matter has been hypothesized as the source of positrons—electrons with a positive charge—in the center of our galaxy. However, this new type of supernova produces a radioactive form of titanium that emits positrons as it decays, potentially explaining the abundance of positrons without the need to postulate dark matte

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