Farthest supernova yet marked death of very massive star

 

Astronomers are reaching ever further back in time, seeking events from the earliest days of the universe. Now, the discovery of the farthest (and thus oldest) supernova ever seen is raising hopes that astronomers will soon detect the explosive deaths of the first stars to form after the universe's birth.

These stars forged the first heavy elements, which helped create smaller and longer-lived stars like our own sun.

The earliest stars looked different from modern stars. The big bang produced only three light elements_hydrogen, helium, and a little lithium_but today, stars form in gas clouds that also contain heavier elements such as carbon and oxygen. These elements radiate away enough energy to eventually cool the clouds. When the clouds cool, they fragment into smaller clumps that collapse to spawn a plethora of mostly small stars.

But such fragmentation wasn't easy early in the universe's life, when stars formed from carbon- and oxygen-free gas clouds that remained warm. Because of their warmth, more gravity was needed to overwhelm the higher gas pressure_so when a cloud collapsed, it produced massive stars rather than small stars.

Astronomer Jeff Cooke of Swinburne University of Technology near Melbourne, Australia, and colleagues have been searching for the most distant, ancient supernovae by examining images from the Canada-France-Hawaii Telescope atop Mauna Kea in Hawaii. To discern even the faintest specks of light, the astronomers combine, or "stack," hundreds of images. In one image, taken in 2006 of a galaxy in Sextans (a faint constellation south of Leo), they spotted a very distant supernova indeed.

To find out just how far away it was, Cooke observed the galaxy's spectrum-- the combined light emitted from its stars, arranged by wavelength_at the Keck I telescope, also atop Mauna Kea. "It was quite exciting," he says. "As the spectrum was reading out, I could see the emission line for one of the features, and when I did a quick back-of-the-envelope calculation for the redshift, I saw how high it was."

The redshift is a measure of the supernova's distance. As the universe expands, it stretches the light waves traveling to us from a distant galaxy, shifting the galaxy's spectral lines to redder wavelengths; the farther the galaxy is and the more expanding space its light has traveled through, the greater its redshift. And as Cooke's team reports online Wednesday in Nature, the supernova's redshift is 3.90, which means it is 12.1 billion light-years from Earth_and it exploded just 1.6 billion years after the big bang. That makes it more than a billion light-years farther than the previous record holder.

Moreover, the supernova is anything but normal. It marked the death of a star that was more than 100 times as massive as the sun. During its brief life, such a star supports its great weight by generating so much light that the pressure of that outward radiation balances the inward pull of gravity. Unfortunately for the star, high-energy gamma rays supply much of this outward pressure, and when two gamma rays meet, they can convert their energy into a pair of particles, an electron and a positron.

This "pair production" robs the star of the support that the gamma rays' pressure had been providing. As a result, Cooke says, "The whole star collapses in on itself. It's one giant thermonuclear bomb, and it's incredibly bright." A pair-instability supernova emits about 10 times as much light as the brightest normal supernovae, which occur when white dwarf stars explode. Pair-instability supernovae are so rare that observers have previously seen only one good candidate_and that was in a fairly nearby galaxy.

Astronomer Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, calls the discovery of the distant pair-instability supernova a breakthrough. "It's the first demonstration that such events do take place at early cosmic times, and I think we will find many more of them in the future," he says. Astronomer Volker Bromm of the University of Texas, Austin, says: "This is a very, very promising sign for what we can expect in the coming years."

Cooke's team has also detected another pair-instability supernova 10.4 billion light-years from Earth. Neither supernova arose from a star that formed from pristine gas, so neither represents the very first generation of stars to form after the big bang. But the two explosions suggest that pair-instability supernovae_and thus very massive stars_were more common during the first few billion years of the universe's life than they are today.

- - -

This is adapted from ScienceNOW, the online daily news service of the journal Science. http://news.sciencemag.org

Start your day with The Independent, sign up for daily news emails
Sport
England's women celebrate after their 3rd place play-off win against Germany
Women's World CupFara Williams converts penalty to secure victory and bronze medals
Arts and Entertainment
Ricardo by Edward Sutcliffe, 2014
artPortraits of LA cricketers from notorious suburb go on display
News
newsHillary Clinton comments on viral Humans of New York photo of gay teenager
Arts and Entertainment
The gang rape scene in the Royal Opera’s production of Gioachino Rossini’s Guillaume Tell has caused huge controversy
music
ebooks
ebooksAn introduction to the ground rules of British democracy
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Sales Administrator - Spanish Speaking

£17000 - £21000 per annum: Recruitment Genius: This is a fantastic opportunity...

Recruitment Genius: Sales Administrator - German Speaking

£17000 - £23000 per annum: Recruitment Genius: This is a fantastic opportunity...

Recruitment Genius: Sales Administrator - Japanese Speaking

£17000 - £23000 per annum: Recruitment Genius: If you are fluent in Japanese a...

Recruitment Genius: Graphic Designer - Immediate Start

£16000 - £25000 per annum: Recruitment Genius: This is a fantastic opportunity...

Day In a Page

The Greek referendum exposes a gaping hole at the heart of the European Union – its distinct lack of any genuine popular legitimacy

Gaping hole at the heart of the European Union

Treatment of Greece has shown up a lack of genuine legitimacy
Number of young homeless in Britain 'more than three times the official figures'

'Everything changed when I went to the hostel'

Number of young homeless people in Britain is 'more than three times the official figures'
Compton Cricket Club

Compton Cricket Club

Portraits of LA cricketers from notorious suburb to be displayed in London
London now the global money-laundering centre for the drug trade, says crime expert

Wlecome to London, drug money-laundering centre for the world

'Mexico is its heart and London is its head'
The Buddhist temple minutes from Centre Court that helps a winner keep on winning

The Buddhist temple minutes from Centre Court

It helps a winner keep on winning
Is this the future of flying: battery-powered planes made of plastic, and without flight decks?

Is this the future of flying?

Battery-powered planes made of plastic, and without flight decks
Isis are barbarians – but the Caliphate is a dream at the heart of all Muslim traditions

Isis are barbarians

but the Caliphate is an ancient Muslim ideal
The Brink's-Mat curse strikes again: three tons of stolen gold that brought only grief

Curse of Brink's Mat strikes again

Death of John 'Goldfinger' Palmer the latest killing related to 1983 heist
Greece debt crisis: 'The ministers talk to us about miracles' – why Greeks are cynical ahead of the bailout referendum

'The ministers talk to us about miracles'

Why Greeks are cynical ahead of the bailout referendum
Call of the wild: How science is learning to decode the way animals communicate

Call of the wild

How science is learning to decode the way animals communicate
Greece debt crisis: What happened to democracy when it’s a case of 'Vote Yes or else'?

'The economic collapse has happened. What is at risk now is democracy...'

If it doesn’t work in Europe, how is it supposed to work in India or the Middle East, asks Robert Fisk
The science of swearing: What lies behind the use of four-letter words?

The science of swearing

What lies behind the use of four-letter words?
The Real Stories of Migrant Britain: Clive fled from Zimbabwe - now it won't have him back

The Real Stories of Migrant Britain

Clive fled from Zimbabwe - now it won’t have him back
Africa on the menu: Three foodie friends want to popularise dishes from the continent

Africa on the menu

Three foodie friends want to popularise dishes from the hot new continent
Donna Karan is stepping down after 30 years - so who will fill the DKNY creator's boots?

Who will fill Donna Karan's boots?

The designer is stepping down as Chief Designer of DKNY after 30 years. Alexander Fury looks back at the career of 'America's Chanel'