Stardate 2004-04-06 First Generation of Stars

Ref: http://stardate.org/radio/program.ph...&id=2004-04-06
http://www.utexas.edu/general/stardate/sd20040406.ram

The First Stars

Many of the stars that are visible to the unaided eye are classified
as supergiants -- the most massive stars in the galaxy. They're much
bigger, heavier, hotter, and brighter than our own star, the Sun. A
couple of good examples are Rigel and Betelgeuse, the brightest stars
of Orion, which is low in the southwest in early evening.

Yet even these stars would have been puny compared to the very first
stars, which were born when the universe was quite young -- perhaps
only one or two percent of its current age.

These stars were made only of the elements produced in the Big Bang --
mostly hydrogen and helium. No other elements even existed -- no
oxygen, no carbon, no iron, no gold. All of these elements are
produced inside stars. Since no stars had yet lived, none of the
heavier elements had been made.

Without these elements, the stars grew to enormous proportions.
Computer simulations show that the heaviest stars could have been
thousands of times as massive as the Sun. By comparison, the heaviest
stars in the modern universe are no more than a couple of hundred
times the Sun's mass.

These first-generation stars probably didn't live long, though. Within
a few million years, they would have exploded. Most left behind black
holes. But a few blasted themselves to smithereens, sprinkling the
universe with the elements needed to make the second generation of
stars -- and the first generation of planets. More on that tomorrow.

Script by Damond Benningfield, Copyright 2004

Supporting Material
The First Stars
http://arxiv.org/abs/astro-ph/0311019

First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
http://arxiv.org/abs/astro-ph/0311082

Telling the tale of the first stars
http://arxiv.org/abs/astro-ph/0304468

etc.
http://www.google.com/search?q=first...te%3AarXiv.org

First Star in Universe Born With Help of Dark Matter, Study Says
Ref: http://www.space.com/scienceastronom...ar_011115.html

Astronomers have created a computer simulation showing how the
first star in the universe might have formed, helping to plug a
gap in understanding of the timeline of the early cosmos.

The simulation shows how exotic and invisible "dark matter" formed
clumps that attracted normal matter, which collapsed and formed a
giant star. The result implies that the first light in the
universe was created by a single fiery furnace, not by some
instantaneous creation of a galaxy or cluster of stars.

The study does not represent an actual observation, but scientists
said it provides significant insight into what might have happened
in the first few million years after the Big Bang, when a smooth
and dark universe became lumpy and illuminated.


The research team, led by Tom Abel at the Harvard Smithsonian
Center for Astrophysics, says a lone object developed out of a
cloud of raw material, a first star that became one of many seeds
that later formed the first galaxies.

The first star, along with others that presumably formed soon
after in a similar manner, died quickly and cannot be seen or
studied today. So astronomers have long wondered how such objects
formed.

"Significant progress is being made in this area and we are very
close to finding a solution to how the first stars formed," said
Morris Aizenman, senior science associate in the Mathematical and
Physical Science Directorate of the National Science Foundation.

"Abel's study is a significant step forward," said Aizenman, who
was not involved in the work but has examined the methods and
results.

A paper describing the simulation was published Thursday in
Science Express, an online sister publication to the journal
Science. Greg Bryan at the Massachusetts Institute of Technology
and Michael Norman of the University of California-San Diego
developed the sophisticated computer code used by the team and
also worked on the research.

A simple palette

Most stars today are rich in metals. But the early universe was
metal-free.

Astronomers have long assumed that the first stars must have been
an as-yet-unknown metal-free variety, and that they exploded soon
after they were born, forging metal and flinging it into space.
Later, the more diverse array of material would have been gathered
up to make second- and third-generation stars.

Since it is not yet possible to see these earliest stars,
researchers employ computers to model what might have happened.

The task is complex, but the range of possibilities is simpler
than one might think, because there was little to work with in the
infant universe. Most of the material and processes that makes
modeling today's universe incredibly complex simply didn't exist
back then.

There were no magnetic fields. No space dust. No cosmic rays. And
only a handful of chemical elements existed.

After the Big Bang, estimated to be between 12 and 15 billion
years ago, the universe was composed mostly of dark matter,
invisible particles that are widely accepted to exist but have not
yet been detected. A relatively smooth distribution of dark matter
and some normal matter, mostly hydrogen atoms, permeated the young
cosmos, theorists say.

But lumps and bumps developed, catalysts that were destined to
form something.

The first star

Abel explained for SPACE.com how the new simulation shows the
first star developing, and what his group's findings mean for
theorists.

The process began just 13 million years after the Big Bang. Small
perturbations had formed in the fabric of the universe. After 100
million years, dark matter is attracted to these "density
fluctuations," as researchers call them. Over time, several draw
together to form one larger clump.

Atoms of hydrogen are pulled in, too. The hydrogen is compressed
and heats up, much like the air in a tire warms as you pump more
air into it. Some hydrogen atoms, now pressed more tightly
together, combine to form molecules -- molecular hydrogen.

The result is the development of a molecular cloud, something seen
in our own galaxy today and known to be a precursor to star
formation.

After 155 million years -- an eyeblink in cosmological terms -- a
cloud of normal and dark matter has built up the mass of a million
suns. In the center, a star about the mass of our Sun is born. The
very first star in the universe.

Overindulgence

Nearby, however, at the center of the cloud and surrounding the
new star, there is enough gas to make 200 more suns. The first
star uses its newfound gravity to reel this gas in. The final mass
of the first star is not determined by Abel's simulation, but it
is thought to grow to gargantuan proportions.

There is a limit, however.

Scientists are convinced that a star more than 100 times as
massive as the Sun is forced to explode in what's known as a
supernova.

Given the material available to the first stars in the new model,
they would likely have grown quickly and become so massive as to
explode after just a few million years.

Abel said one of the most significant aspects of the simulation is
that the collapse of material in the cloud happens so rapidly that
it forms just one star, instead of being fragmented into several.
And the first star would have cannibalized any effort to generate
another nearby star.

"The star is so luminous in ultraviolet photons that it destroys
all the hydrogen molecules that would be needed to form other
stars nearby," he explained.

Over the past three decades, other theorists have suggested that
the first objects to form in the universe might have been black
holes or possibly clusters of stars. The new view, if it stands
up, implies that "most of the speculations of the last decades,
which assumed the cloud would fragment, are incorrect," Abel
said.

Long gone

There is no chance of seeing one of these first stars in our
galaxy.

"Since all these stars formed billions of years ago, they have
already exploded by now," Abel said. "However, one is hoping to
see signatures of these first objects in the images of distant
galaxies. They are billions of light years away and hence the most
distant of these galaxies perhaps still host some of the first
stars."

So far, researchers have not spotted the most distant galaxies
thought to have existed, but many believe they are on the
threshold of doing so.

The simulation was done on the SGI Origin2000 supercomputer at the
National Center for Supercomputing Applications at the University
of Illinois. Abel said it is the first such set of calculations to
simultaneously follow the collapse of material from cosmological
scales down to stellar scales.

"The most amazing thing for us is that we can realistically
recreate the events that made the first objects in the universe,"
Abel said.

Supporting Material
The First Stars
http://arxiv.org/abs/astro-ph/0311019

First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy
http://arxiv.org/abs/astro-ph/0311082

Telling the tale of the first stars
http://arxiv.org/abs/astro-ph/0304468

etc.
http://www.google.com/search?q=first...te%3AarXiv.org

First Star in Universe Born With Help of Dark Matter, Study Says
Ref: http://www.space.com/scienceastronom...ar_011115.html

Astronomers have created a computer simulation showing how the
first star in the universe might have formed, helping to plug a
gap in understanding of the timeline of the early cosmos.

The simulation shows how exotic and invisible "dark matter" formed
clumps that attracted normal matter, which collapsed and formed a
giant star. The result implies that the first light in the
universe was created by a single fiery furnace, not by some
instantaneous creation of a galaxy or cluster of stars.

The study does not represent an actual observation, but scientists
said it provides significant insight into what might have happened
in the first few million years after the Big Bang, when a smooth
and dark universe became lumpy and illuminated.


The research team, led by Tom Abel at the Harvard Smithsonian
Center for Astrophysics, says a lone object developed out of a
cloud of raw material, a first star that became one of many seeds
that later formed the first galaxies.

The first star, along with others that presumably formed soon
after in a similar manner, died quickly and cannot be seen or
studied today. So astronomers have long wondered how such objects
formed.

"Significant progress is being made in this area and we are very
close to finding a solution to how the first stars formed," said
Morris Aizenman, senior science associate in the Mathematical and
Physical Science Directorate of the National Science Foundation.

"Abel's study is a significant step forward," said Aizenman, who
was not involved in the work but has examined the methods and
results.

A paper describing the simulation was published Thursday in
Science Express, an online sister publication to the journal
Science. Greg Bryan at the Massachusetts Institute of Technology
and Michael Norman of the University of California-San Diego
developed the sophisticated computer code used by the team and
also worked on the research.

A simple palette

Most stars today are rich in metals. But the early universe was
metal-free.

Astronomers have long assumed that the first stars must have been
an as-yet-unknown metal-free variety, and that they exploded soon
after they were born, forging metal and flinging it into space.
Later, the more diverse array of material would have been gathered
up to make second- and third-generation stars.

Since it is not yet possible to see these earliest stars,
researchers employ computers to model what might have happened.

The task is complex, but the range of possibilities is simpler
than one might think, because there was little to work with in the
infant universe. Most of the material and processes that makes
modeling today's universe incredibly complex simply didn't exist
back then.

There were no magnetic fields. No space dust. No cosmic rays. And
only a handful of chemical elements existed.

After the Big Bang, estimated to be between 12 and 15 billion
years ago, the universe was composed mostly of dark matter,
invisible particles that are widely accepted to exist but have not
yet been detected. A relatively smooth distribution of dark matter
and some normal matter, mostly hydrogen atoms, permeated the young
cosmos, theorists say.

But lumps and bumps developed, catalysts that were destined to
form something.

The first star

Abel explained for SPACE.com how the new simulation shows the
first star developing, and what his group's findings mean for
theorists.

The process began just 13 million years after the Big Bang. Small
perturbations had formed in the fabric of the universe. After 100
million years, dark matter is attracted to these "density
fluctuations," as researchers call them. Over time, several draw
together to form one larger clump.

Atoms of hydrogen are pulled in, too. The hydrogen is compressed
and heats up, much like the air in a tire warms as you pump more
air into it. Some hydrogen atoms, now pressed more tightly
together, combine to form molecules -- molecular hydrogen.

The result is the development of a molecular cloud, something seen
in our own galaxy today and known to be a precursor to star
formation.

After 155 million years -- an eyeblink in cosmological terms -- a
cloud of normal and dark matter has built up the mass of a million
suns. In the center, a star about the mass of our Sun is born. The
very first star in the universe.

Overindulgence

Nearby, however, at the center of the cloud and surrounding the
new star, there is enough gas to make 200 more suns. The first
star uses its newfound gravity to reel this gas in. The final mass
of the first star is not determined by Abel's simulation, but it
is thought to grow to gargantuan proportions.

There is a limit, however.

Scientists are convinced that a star more than 100 times as
massive as the Sun is forced to explode in what's known as a
supernova.

Given the material available to the first stars in the new model,
they would likely have grown quickly and become so massive as to
explode after just a few million years.

Abel said one of the most significant aspects of the simulation is
that the collapse of material in the cloud happens so rapidly that
it forms just one star, instead of being fragmented into several.
And the first star would have cannibalized any effort to generate
another nearby star.

"The star is so luminous in ultraviolet photons that it destroys
all the hydrogen molecules that would be needed to form other
stars nearby," he explained.

Over the past three decades, other theorists have suggested that
the first objects to form in the universe might have been black
holes or possibly clusters of stars. The new view, if it stands
up, implies that "most of the speculations of the last decades,
which assumed the cloud would fragment, are incorrect," Abel
said.

Long gone

There is no chance of seeing one of these first stars in our
galaxy.

"Since all these stars formed billions of years ago, they have
already exploded by now," Abel said. "However, one is hoping to
see signatures of these first objects in the images of distant
galaxies. They are billions of light years away and hence the most
distant of these galaxies perhaps still host some of the first
stars."

So far, researchers have not spotted the most distant galaxies
thought to have existed, but many believe they are on the
threshold of doing so.

The simulation was done on the SGI Origin2000 supercomputer at the
National Center for Supercomputing Applications at the University
of Illinois. Abel said it is the first such set of calculations to
simultaneously follow the collapse of material from cosmological
scales down to stellar scales.

"The most amazing thing for us is that we can realistically
recreate the events that made the first objects in the universe,"
Abel said.