There are
currently more stars in the cosmos than any one person could ever count. Our
galaxy alone contains about 400 billion. But it wasn't always this way.
For many
millions of years after our universe first formed no stars existed, and then
there was one. That primordial
star was likely a massive blazing behemoth that burned brighter and faster
than any star around today.
A new
computer model now suggests that it also formed much earlier than previously
thought.
Other
studies have estimated that the first star sparked into existence some 155
million years after our universe exploded into life in the Big Bang
13.7 billion years ago.
The new
simulation indicates that this event occurred much earlier, when the universe
was only 30 million years old. It also suggests that it took about another 370
million years for the first galaxy as massive as our own Milky
Way to form.
The model
is detailed in an upcoming issue of the Monthly Notices for the Royal
Astronomical Society.
When
exactly?
Using
detailed computer simulations, astronomers reconstructed the conditions under
which the first star was born and even the precise sequence of steps that
occurred soon after to allow other stars, and eventually galaxies, to form.
Astronomers
suspect, for example, that the first star
formed in a dense cloud of dark matter and gas. They also think that many
present-day galaxies are the products of mergers
between much smaller galaxies during the early days of our universe.
Estimating when
the first star formed, however, has been difficult. That's because even the
most powerful supercomputers can only simulate small portions of the universe
at a time.
"To
estimate when the first stars formed, we must remember that the first 100,000
solar mass clumps collapsed in regions that happened to have particularly high
densities early on," said study leader Rennan Barkana, an astrophysicist
at the University of Tel Aviv in Israel.
"There
were initially only a few such regions in the entire universe, so a simulation
that is limited to a small volume is unlikely to find such [regions] until much
later," he said.
The model
created by Barkana and his colleagues gets around this problem by approximating
how many dark
matter clumps large enough to host the first star were present at different
times of the universe.
"We
integrated this over time to find the total expected number of observable
stars," Barkana said. The researchers then crosschecked their predictions
with simulations.
Primal
stars
Even by
stellar standards, the primordial star was a monster. It likely had a mass of
about 100 times that of our Sun and it would have spewed out vast amounts of
energetic radiation, especially in the ultraviolet range. Had human eyes been
around to see it, it would have appeared blue-violet in color.
The first
star shone brighter than most stars in existence today and it zipped through
its stellar life in only 2 million to 3 million years, compared to the
several-billion-year lifetimes that some of today's stars have. Our Sun is
middle-aged now and has been around for 4.6 billion years.
Scientists
think that when it spent its fuel, the first star exploded in a titanic stellar
cataclysm called a supernova,
flinging heavy elements forged during the star's lifetime into space, setting
the stage for the next generation of stars.
"After
a short time, stars began appearing in greater abundance throughout the
universe," Barkana told SPACE.com.
The second
generation stars likely formed within about a million years after the first,
Barkana said. Within five million years, there were about 100 stars; within ten
million years, 10,000 celestial orbs of fire were lighting up the heavens.
Unlike that
first star, which was made up mostly of hydrogen and helium, the stars that
came after contained heavier elements, such as carbon and iron.
Still
detectable
Light once
emitted by the first star might still be detectable, Barkana said.
In space,
the older an object is, the farther away it is. It would require a telescope
about 100 million times more sensitive than the Hubble Space Telescope to
observe light from the first star, but it's not impossible.
"If the
first star was indeed massive and produced in its death a huge supernova
explosion or gamma ray burst, then we might have a chance to see the explosion
with the instruments planned for the coming decade," Barkana said.
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