How the first stars were born
2008-08-01 11:26
Washington - The first object to
brighten the dark, primordial universe after the Big Bang was
the tiny seed of a star that rapidly grew into a behemoth 100
times more massive than the sun, scientists said on Thursday.
This first generation of stars apparently lived hard and
died quickly.
While our sun may live 5 billion years, this
first generation of stars likely lasted only a slim fraction of
that - about 1 million years, the researchers said.
Scientists think the universe was born in a Big Bang
explosion 13.7 billion years ago and has been expanding ever
since.
But they have struggled to understand how the first
stars formed in the aftermath of this cataclysm.
Japanese and US astronomers ran a sophisticated computer
simulation that showed how some of the hydrogen and helium
gases strewn throughout the young universe came together to
form the first generation of stars.
'First sources of light'
"These stars are thought to be the first sources of light
and also the first sources of heavy elements such as carbon,
oxygen and iron," Naoki Yoshida of Nagoya University in Japan,
who worked on the study published in the journal Science, said
in a telephone briefing.
"If we want to understand how things came about and look
the way they do now, we have to go back in time and understand
how stars looked when they first began to form," added Lars
Hernquist of Harvard University in Massachusetts.
At the time, the universe was about 20 times as compact as
it is now, Hernquist said. "We think that early in the
universe, the only elements that existed were hydrogen and
helium, with trace amounts of lithium," Hernquist added.
This matter was generally very smoothly distributed
throughout the universe, but some regions had greater
concentrations of it than others, the researchers said.
The effects of the gravity from this matter drew in more
and more material over time, setting in motion clouds of
hydrogen and helium that came together as a "protostar" - the
seed of a much larger star.
'First protostar'
The first protostar was born about 300 million years after
the Big Bang, the researchers said.
Nuclear reactions inside
the protostar made it the first object to cast starlight in
what some astronomers call the "cosmic dark ages," they added.
It was a relatively tiny object at first, 1 percent the
mass of the sun. But within about 10 000 years - "the blink of
an eye," according to the researchers - it grew into a giant
full-fledged star at least 100 times the sun's mass.
While none of the stars survive today, their influence
remains.
The processes churning inside the stars synthesised the
universe's first heavy elements.
In dying, these stars may have
blasted this stuff back into space to become building blocks of
future stars and planets composed of many more elements.
Hernquist said these stars may have died in a very bright
supernova or might have collapsed in on themselves, forming
black holes with relatively little of their material ejected
into space as ingredients for future stars.