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Stars have onion-like layers that blow off in fiery explosions before a final killing blow—a supernova—turns them into black holes, according to a new theory of star death.

These repetitive blasts are too powerful to be caused by stellar winds, as previously believed—so they must come from a new type of explosion originating in the star's interior, astronomers say.

The theory was advanced this week in a study led by Nathan Smith, an astronomer at the University of California, Berkeley.

Using ground-based telescopes, Smith took a close look at the Homunculus Nebula, the cast-off material from the 1843 explosion of the nearby star Eta Carinae, the most luminous star in the Milky Way (see photo below.)




That explosion suddenly and mysteriously brightened the star.

In the nebula, Smith discovered new, faster moving wisps of gas—too fast to be accounted for by stellar winds.

"We still don't know what the mechanism is that would initiate the explosion in the first place," Smith said, "but at least now we know that there was an explosion that we need to explain."
Double the Power

Researchers had already observed non-fatal explosions on other late-stage stars. Sometimes called "supernova imposters," the blasts are even less well understood than supernovae.

Using two telescopes at Cerro Tololo Inter-American Observatory and the International Gemini Observatory in Chile, Smith took another look at both the Homunculus Nebula and another shell of cast-off material, estimated to be a thousand years old.

Most of the material from both blasts is crawling along at about 1.5 million miles per hour (650 kilometers per second). But Smith's newfound gas filaments are moving much faster, catching up to the materials from the thousand-year-old blast.

The finding potentially doubles estimates for the power of Eta Carinae's 1843 eruption, he said.

Not New?

Douglas Currie, an astrophysicist at University of Maryland at College Park, reported some fast-moving gas jets in Homunculus as far back as 2002, but he says the speeds reported in the new paper are significantly faster—up to double—than what has been seen before.

He doesn't agree that Smith's theory is necessarily new, since other researchers have previously suspected causes of the fast-moving gas other than stellar wind.

"I would call this a further and strong piece of evidence showing that it is a different kind of explosion," he said.

But study leader Smith said that the old speeds were on the edge of what could be produced by stellar winds—and the new speeds, even if only slightly faster—beget new questions.

He said the results "may change our interpretation of what happened in the 1843 event, and what that means for our understanding of the most massive stars."

"It means, essentially, that we still don't fully understand what is going on in the deep interiors of massive stars shortly before they die."

About picture 1 : Six red panda cubs gather around a food bowl during their unveiling at Fuzhou Panda World. The research center bred ten cubs this year. Eight survived.

The World Conservation Union lists the species as endangered. Deforestation of their high-altitude habitat is the primary threat.

Adult red pandas—which look more like raccoons than like their namesake bears—reach the size of a house cats, though the red pandas' bushy tails add an additional 18 inches (46 centimeters).

about picture 2 : Lacking eyelids and true eyelashes, a New Caledonian crested gecko at the Wildlife Conservation Society's Bronx Zoo licks its eyeballs to keep them moist in a photo released last week.

The geckos are native to their namesake French territory in the South Pacific Ocean. Scientists thought the species was extinct until a population was rediscovered in 1994.

Today the gecko is widely kept in the pet trade. Its conservation status is under review by the International Union for the Conservation of Nature.

about picture 3 : How small is a Kihansi spray toad at birth? This photo of a one-week-old at the Wildlife Conservation Society's Bronx Zoo gives an idea.

The toads are native to a lone gorge in Tanzania, though the conservation group believes the species is extinct in the wild due to habitat destruction, disease, and climate change.

The society has bred the toads—which give birth to live young rather than lay eggs—for seven years and plans to reintroduce some to Tanzania.

about picture 4: Surf's up, pooch! A dog shakes after catching a wave in the small-dog heat at the third annual Surf Dog Surf-A-Thon hosted by the Helen Woodward Animal Center.

The surf dogs raise money to support the shelter by catching as many waves as they can in a half-hour session. Sponsors make a per-wave pledge. The event's champion won a trip to K-59, a surf spot in El Salvador.

An early whale had large back legs, a tail like a dog's, and a hip-wiggling swimming style, according to a new fossil study. The discovery helps pinpoint the advent of "modern" whale flukes to between 38 and 40 million years ago, scientists say.

Flukes are the two wide, flat triangular lobes on a whale's back end and are made of skin and connective tissue, with bones in the middle.

Scientists have known whales evolved from semiaquatic, four-footed creatures with long, thin tails to today's fully aquatic mammals with fluked tails, no back legs, and flippers instead of front legs.

But it was previously unknown when the tail flukes first arose in the whale family tree.

"What's interesting about this animal is that it had these back legs that it used to push itself through the water," said study author Mark D. Uhen, a paleontologist from the Alabama Museum of Natural History.

"This animal didn't have flukes, but the ones just a little bit younger [geologically] did. So we can really narrow that time frame now."

Uhen's study is detailed in the latest issue of the Journal of Vertebrate Paleontology.

Fossil Puzzle

Amateurs found different parts of the newly described fossils over time in Coffeeville Landing, Alabama.

After the various fossil parts were brought to the University of Alabama in 2005, Uhen realized that all the pieces belonged to the same individual of the species Georgiacetus vogtlensis. "This is not a new species," Uhen said. "What's significant about it is that we learned more about a species that we already knew." After analyzing the fossils for almost three years, Uhen concluded the individual had a tail, but no fluke, and that Georgiacetus wiggled its hips and moved its entire trunk up and down through the water to move forward—a swim stroke whales no longer use.

"We knew some fossil whales had a tail fluke from slightly younger [fossils]. But we hadn't had decent tail vertebrae to tell where [in time] the whales had tails and where they didn't," Uhen said. "This one little vertebra tells us that Georgiacetus vogtlensis didn't have a tail fluke."

Surprise

Jonathan Geisler, of Georgia Southern University, said the new findings, if true, would force a rethink of early whale migrations.

In a 2005 paper Geisler and colleauges hypothesized that the evolution of flukes helped early whales scatter around the world from their birthplace in South Asia.

"If Georgiacetus, which is known only from North America, did not have tail flukes,"—as the new study suggests—"then our hypothesis would be wrong, and we would have to look elsewhere to explain the dispersal of early whales into the different ocean basins," said Geisler, who was not involved with the current study.

According to Geisler, the findings are a surprise, because previously evidence about the base of the tail in Georgiacetus suggested tail flukes.

"I would have guessed that it did have flukes," he said. "Of course that is the great aspect of paleontology—new fossils can lead to new understandings."