Tuesday, May 08, 2007

Massive Star's Explosion Triggers Renewed Interest in Stellar Lifecycles

A super-massive star that exploded into a supernova last September is giving astronomers and astrophysicists some new insights into stellar evolution. Yahoo News Reuters excerpt:

WASHINGTON (Reuters) - A gargantuan explosion ripped apart a star perhaps 150 times more massive than our sun in a relatively nearby galaxy in the most powerful and brightest supernova ever observed, astronomers said on Monday. And there is one such star in our own Milky Way galaxy that appears to be on the brink of dying in just such a supernova.

The exploding star's dramatic death may have come in a rare type of supernova reserved for "freakishly massive" stars that astronomers had speculated about but never previously witnessed. The supernova, designated as SN 2006gy, occurred 240 million light years away in a galaxy called NGC 1260, and was studied using observations from NASA's orbiting Chandra X-ray Observatory as well as earthbound optical telescopes.

The supernova was discovered in September 2006, and stands as far and away the most powerful and brightest ever observed, Smith said. "In fact, even after the better part of a year, well after 200 days, it has faded somewhat but it's still about as bright as a normal supernova at its peak," Smith said.

A supernova marks a star's death in a spectacular explosion. Scientists say these events play a crucial role in creating heavy elements through nuclear fusion and synthesis and then expelling them into space, seeding the cosmos with metals. The scientists ruled out a possible alternative explanation that what they were witnessing was the explosion of a white dwarf star with a mass only a bit more than the sun.

Astrophysicist Mario Livio said the supernova may have resulted from a type of explosion mechanism that had existed only in theoretical calculations. He said the first generation of stars in the universe may have died in such a manner.

In a normal supernova, the core of a star collapses when it exhausts its fuel, and forms either a neutron star or a black hole, with scant heavy elements blown into space. But this supernova appears to be the result of the core not collapsing but being obliterated in an explosion blasting all its material into space, the scientists said.

Dave Pooley of the University of California at Berkeley said this star appears similar to Eta Carinae, a star perhaps 100 to 120 times the mass of the sun located 7,500 light years away within the Milky Way. There has not been a supernova in our galaxy in more than 400 years, Pooley said.

If Eta Carinae were to burst into a supernova, Pooley said, "It would be so bright that you would see it during the day, and you could even read a book by its light at night."

Livio said Eta Carinae had an incredible eruption during the 19th century that left it in an hourglass shape. He said it could explode at any time. "This could happen tomorrow, it could happen 1,000 years from now," Livio said. "Is there a risk to life on Earth as a result of this explosion? Well, not very likely." Livio said Earth could be affected if there were a gamma ray burst that potentially could harm the atmosphere and life, but the chances of this aiming directly at Earth are slim.

My opening about this star having exploded last September is obviously incorrect. This star exploded 240 million years ago, and it's light is just now reaching our eyes. Light travels 186,000 miles (300,000 kilometers) every second. It therefore travels roughly 5.86 trillion miles (about 9.44 trillion kilometers) in a year. That works out to about 1.41 x 10 to the 21st power miles (2.265 x 10 to the 21st power kilometers). If I've done my math correctly, that means it would take one about 7.11 x 10 to the 15th power years to reach this dead star at the rate of 55 miles per hour.

All kidding aside, any information we get from these observations is important because, as the excerpt details, we have a similarly large and unstable monster of a star in our own galaxy. Eta Carinae, which lies embedded in the plane of the southern Milky Way (alas too far to glimpse from the latitude where I sit typing this post, although I did get more than one glance at that region of the sky when I visited Australia in January and February of 2005) has fascinated astronomers for decades, and the readings gleaned from these observations will only enhance that fascination as astronomers and astrophysicists attempt to predict what will happen to this huge star.

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