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Did antimatter 'factory' spark brightest supernova?

07 May 2007
NewScientist.com news service
David Shiga

The brightest supernova ever recorded may have been triggered by an exotic process involving antimatter in an extremely massive star, a new study says. The explosion may offer a rare glimpse of how the universe's first generation of stars died.

The explosion was first spotted on 18 September 2006 and named SN 2006gy. It quickly became apparent that it was something out of the ordinary.

To begin with, it broke the record for the intrinsically brightest supernova ever recorded. Other events, like SN 1987A, have appeared brighter to us, but only because they took place much closer to Earth.

An early analysis of the explosion suggested it might be the result of a stellar corpse called a white dwarf star smashing into the core of a bloated red giant star.

But new evidence suggests it was something even more exotic. It now appears to have been an extremely massive star meeting its end in a highly unusual way that involves the production of antimatter, according to a team of astronomers led by Nathan Smith of the University of California in Berkeley, US.

Exotic process

The researchers used visible and infrared observations from facilities such as the Lick Observatory on Mount Hamilton, California, as well as X-ray measurements from NASA's Chandra space telescope to investigate the nature of the explosion. Watch an animation comparing views of SN 2006gy at different wavelengths.

With 100 times the energy of a typical supernova explosion, SN 2006gy was simply too energetic to be explained by the explosion of a lightweight object like a white dwarf star, even if it were to collide with the core of a red giant, says team member Craig Wheeler of the University of Texas in Austin, US.

"That kind of explanation could not produce the energy we're seeing," he told New Scientist.

The researchers argue instead that it was the explosion of a very heavy star that was born with as much as 150 times the mass of the Sun. Heavy stars normally collapse to form black holes at the end of their lives, but it has long been theorised that especially heavy ones could instead be completely ripped apart by an exotic process called pair instability.

Pressure drop

In the bowels of such a stellar titan, the high temperature and pressure conditions are ripe for the conversion of light into particle pairs in which one particle is an electron and the other is its antimatter counterpart, a positron.

This causes a drop in pressure that makes the star unstable. It begins to contract, which eventually ignites runaway nuclear reactions that rip the star to shreds. Watch an animation of a pair instability supernova.

The huge amount of radioactive material spewed into space from the shredded core of such a star could explain the extreme brightness of SN 2006gy, the researchers say.

"It isn't quite proof yet, but it smells kind of like a pair formation supernova," Wheeler says. "I think it's the opening of a new chapter in supernova research."

Young stars

Avishay Gal-Yam of Caltech in Pasadena, US, a member of the team that initially suggested the white dwarf collision scenario, says in light of the new data, a scenario involving a massive star looks more likely to be correct.

He and colleagues had initially been sceptical of that possibility because only old, relatively lightweight stars appeared to lie within the galaxy that SN 2006gy exploded in, NGC 1260, which is 240 million light years from Earth.

"Additional, very sensitive observations of the core show that it has just a [few] young, massive stars, right where the supernova exploded," Gal-Yam told New Scientist. "So an explanation of the supernova which requires a massive star, which initially seemed unlikely, now becomes more plausible."

He says the idea that the massive star exploded as a result of the exotic pair instability scenario is an exciting but speculative possibility that would need confirmation with future observations.

There had previously been some speculation that another unusual supernova, SN 2006jc, was also the result of pair instability.

First stars

But Alex Filippenko of Caltech, who is a member of Smith's team, says that is unlikely. SN 2006jc was intrinsically much dimmer, suggesting that it spewed far less radioactive material into space, he says. "I think it very unlikely that the same physical mechanism operated in SN 2006jc as in SN 2006gy," he told New Scientist.

SN 2006gy may have offered an unprecedented view of the process that killed off the universe's first stars, he says. The event shows that some extremely massive stars can avoid collapsing to form a black hole, and instead seed the universe with heavy elements when they die. Heavy elements are needed for the formation of planets and life as we know it. "The first-generation stars may have produced and dispersed heavy elements in this manner," Filippenko says.

The event may also presage an even more spectacular explosion in our cosmic backyard. The star that produced SN 2006gy appears to have blown off a lot of material prior to the explosion.

One of the most massive stars in our own galaxy, Eta Carinae, has also been shedding large amounts of material, suggesting that it, too, might be about to die in a pair instability supernova, Filippenko says. If it does go, it will appear amazingly bright because at 7500 light years, it is much closer than SN 2006gy was.

[ Wikipedia article on Eta Carinae ]



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In their November issue for 2004, National Geographic magazine published an excellent article on the reality of evolution. The pages are reproduced here for study using the DjVu image compression format, available as a free plugin from LizardTech Software. Was Darwin Wong? Cover, Nov 2004 National Geographic

 

A plaque commemorating the astronauts who died in the tragic accident of the Space Shuttle Columbia is mounted on the back of the Mars Exploration Rover Spirit's high-gain antenna. The plaque was designed by Mars Exploration Rover engineers. The astronauts are also honored by the new name of the rover landing site, the Columbia Memorial Station. This image was taken by the Navigation Camera on Spirit. in remembrance

Articles of Interest

2007/05/10 Ancient Star Nearly as Old as the Universe Live Science Long before our solar system formed and even before the Milky Way assumed its final spiral shape, a star slightly smaller than the Sun blazed into life in our galaxy, formed from the newly scattered remains of the first stars in the universe.
2007/05/10 Solar System Is "Bullet Shaped" National Geographic Our solar system flies through space in the shape of a speeding bullet, according to data from NASA's two Voyager spacecraft.
2007/05/09 "Encyclopedia of Life" to Catalog All Species on Earth National Geographic Scientists announced plans today to put descriptions, pictures, video, and sounds of the world's estimated 1.8 million named species on the Internet for free.
2007/05/08 Star dies in monstrous explosion BBC News A massive star about 150 times the size of the Sun exploded in what could be a long-sought new type of supernova, Nasa scientists have said.
2007/05/07 Could Light Behave As A Solid? A New Theory Science Daily “Solid light will help us build the technology of this century,” says Dr Andrew Greentree of the School of Physics at the University of Melbourne.
2007/05/07 How The Brain's Backup System Compensates For Stroke Science Daily Researchers have pinpointed in humans how a "backup" brain region springs into action to compensate for disruption of a primary functional area, as happens during stroke. Their finding offers new insight into how the brains of stroke victims can quickly reorganize to enable the beginning of recovery of movement.
2007/05/07 Nanotechnology May Be Used To Regenerate Tissues, Organs Science Daily Research at Northwestern University has shown that a combination of nanotechnology and biology may enable damaged tissues and organs to heal themselves.
2007/05/04 Global Warming Can Be Stopped, World Climate Experts Say National Geographic Humans have the means to drastically cut greenhouse gas emissions and avoid the catastrophic consequences of global warming, a major climate report released today concludes.
2007/05/03 "Weird" New Planet Weighs as Much as 2,500 Earths National Geographic With temperatures ranging from 1000 to 2000°C, gravity 15 times stronger than Earth's, and a year that lasts just 5.6 of our days, HAT-P-2b is not a planet you'd want to visit for vacation.
2007/05/03 Liquid Mercury: Tiny Planet Has Molten Core National Geographic Mercury's metallic core is at least partially liquid, say scientists who studied the tiny planet using Earth-based radio telescopes.
2007/05/03 Pioneer US astronaut dies aged 84 BBC News
US space pioneer Walter Schirra, one of the original Mercury Seven astronauts who flew Nasa's earliest flights, has died aged 84.
2007/05/03 Volcanic Explosion on Mars Created Weird Formation National Geographic A mysterious area of layered bedrock on Mars that has puzzled scientists was formed by a volcanic explosion, new research shows.
2007/04/25 New 'super-Earth' found in space BBC News Astronomers have found the most Earth-like planet outside our Solar System to date, a world which could have water running on its surface.
2007/04/06 Belief in Reincarnation Tied to Memory Errors Live Science People who believe they have lived past lives as, say, Indian princesses or battlefield commanders are more likely to make certain types of memory errors, according to a new study.
2007/04/06 Billions face climate change risk BBC News Billions of people face shortages of food and water and increased risk of flooding, experts at a major climate change conference have warned.
2007/04/06 Major study questions value of school software e-School News The use of certain educational software programs to help teach reading and math did not lead to higher test scores after a year of implementation, according to a major federal report released April 5.
2007/04/06 Star's odd double explosion hints at antimatter trigger New Scientist A star that survived a massive explosion – only to be destroyed in a second blast just two years later – has piqued the curiosity of astronomers. Its bizarre death might be due to the production of antimatter in its core towards the end of its life.
2007/04/05 Did Earliest Human Ancestors Have More Apelike Faces? National Geographic The earliest direct ancestors of modern humans may have looked more like apes than previously thought, a new study suggests.
2007/04/05 U.S. Southwest Drought Could Be Start of New Dust Bowl National Geographic The unprecedented drought that has gripped the southwestern United States isn't almost over, researchers say, it may have only just begun. ... That's the consensus of all but 1 of the 19 climate models used as the basis for this week's upcoming report from the Intergovernmental Panel on Climate Change (IPCC), according to a new analysis.
2007/03/28 Paul Cohen, emeritus professor and winner of world's top math prize, dies at 72 Stanford News Cohen won two of the most prestigious awards in mathematics—in completely different fields. He won the American Mathematical Society's Bôcher Prize in 1964 for analysis and the Fields Medal, considered the "Nobel Prize" of mathematics, in 1966 for logic.
2007/03/16 Antarctic Glaciers' Sloughing Of Ice Has Scientists at a Loss Washington Post Some of the largest glaciers in Antarctica and Greenland are moving in unusual ways and are losing increased amounts of ice to the sea, researchers said yesterday.
2007/03/15 Icy map to probe Europa's secrets BBC News Scientists have produced a global geological map of Jupiter's moon Europa, which has been proposed as a destination for a future space mission.
2007/03/12 Darwin's wife's diaries go online BBC News The diaries of the wife of naturalist Charles Darwin have been published online.

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