4306 - THE FIRST STARS? - The James Webb Space Telescope (JWST) has glimpsed light from ionized helium in a distant galaxy, which could indicate the presence of the universe’s very first generation of stars.
------------------------------ 4306 - THE FIRST STARS?
- These
long-sought, “Population III” stars,
would have been huge balls of hydrogen and helium sculpted from the universe’s
primordial gas. Theorists started imagining these first fireballs in the 1970s,
hypothesizing that, after short lifetimes, they exploded as supernovas, forging
heavier elements and spewing them into the universe.
-
- That star stuff
later gave rise to Population II stars more abundant in heavy elements, then
even richer Population I stars like our sun, as well as planets, asteroids,
comets and eventually life itself.
-
- JWST is
transforming vast swaths of astronomy being capable of peering far enough away
in space and time to see them. Already, the gigantic floating telescope has
detected distant galaxies whose unusual brightness suggests they may contain
Population III stars.
-
- About 400,000
years after the Big Bang, electrons, protons and neutrons settled down enough
to combine into hydrogen and helium atoms. As the temperature kept dropping,
dark matter gradually clumped up, pulling the atoms with it. Inside the clumps,
hydrogen and helium were squashed by gravity, condensing into enormous balls of
gas until, once the balls were dense enough, nuclear fusion suddenly ignited in
their centers. The first stars were born.
-
- The German
astronomer Walter Baade categorized the stars in our galaxy into types I and II
in 1944. The former includes our sun and other metal-rich stars; the latter
contains older stars made of lighter elements.
-
- The idea of
Population III stars entered the literature decades later. In a 1984 paper the
British astrophysicist Bernard Carr described the vital role this original
breed of star may have played in the early universe. Their heat or explosions
could have reionized the universe and their heavy-element yield could have
produced a burst of pregalactic enrichment, giving rise to later stars richer
in heavier elements.
-
- The stars could
have grown to immense sizes, measuring anywhere between a few hundred and
100,000 times more massive than our sun, because of the large volume of
hydrogen and helium gas available in the early universe.
-
- Those at the
heavier end of the range, supermassive stars, would have been relatively cool,
red and bloated, with sizes that could encompass almost our entire solar
system. Denser, more modestly sized variants of Population III stars would have
shone blue hot, with surface temperatures of some 50,000 degrees Celsius,
compared to just 5,500 degrees for our sun.
-
- In the present
universe, clouds of gas fragment into lots of small stars. But the simulations
showed that gas clouds in the early universe, being much hotter than modern
clouds, couldn’t as easily condense and were therefore less efficient at star
formation. Instead, entire clouds would collapse into a single, giant star.
-
- Their immense
proportions meant the stars were short-lived, lasting a few million years at
most. (More massive stars burn through their available fuel more quickly.) Population III stars wouldn’t have lasted
long in the history of the universe, perhaps a few hundred million years as the
last pockets of primordial gas dissipated.
-
- In 1999,
astronomers at the University of Colorado predicted that the stars should
produce a telltale signature: specific frequencies of light emitted by helium
II, or helium atoms that are missing an electron, when each atom’s remaining
electron moves between energy levels.
The helium emission is not actually originating from within the stars
themselves, rather, it was created when energetic photons from the stars’ hot surfaces
plowed into gas surrounding the star.
-
- In 2015
astronomers detected a possible hint of a helium II signature in a distant,
primitive galaxy that might have been linked to a group of Population III
stars. Seen as it appeared 800 million years after the Big Bang, the galaxy
looked as if it might contain the first evidence of the first stars in the
universe.
-
- JWST, launched in December 2021, with its enormous
mirror and unprecedented sensitivity to infrared light, can peer more easily
into the early universe than any telescope before it. (Because light takes time
to travel here, the telescope sees faint, faraway objects as they appeared long
ago.) The telescope can also do spectroscopy, breaking up light into its
component wavelengths, which allows it to look for the helium II hallmark of
Population III stars.
-
- Analyzed
spectroscopy data for more than 2,000 of
JWST’s targets in a distant galaxy seen as it appeared just 620 million
years after the Big Bang. The galaxy is
split into two pieces. Analysis showed
that one half seems to have the key signature of helium II mixed with light
from other elements, potentially pointing to a hybrid population of thousands
of Population III and other stars. Spectroscopy of the second half of the
galaxy has yet to be done, but its brightness hints at a more Population III-rich
environment.
-
- The Webb Space
telescope will rewrite cosmic history if It works. Astronomers propose to use the gravity of
giant clusters of galaxies to see individual stars in the early universe. Using
a massive object like a cluster to warp light and magnify more distant objects
(a technique known as gravitational lensing) is a common way astronomers obtain
views of distant galaxies.
-
- And there
remains the tantalizing possibility that some of the unexpectedly bright
galaxies already seen by JWST in the early universe could owe their brightness
to massive Population III stars.
-
- Webb Space
Telescope's discovery of the universe's oldest black holes is also giving
astronomers some vital clues for how they came to be. JWST has spotted the oldest black hole ever
seen, an ancient monster with the mass of 1.6 million suns lurking 13 billion
years in the universe's past. Looking
back in time to our universe's beginnings, the supermassive black hole at the
center of the infant galaxy GN-z11 was spotted just 440 million years after the
universe began.
-
- Closer to the
present-day, black holes are born from
the collapse of giant stars. They grow by ceaselessly gorging on gas, dust,
stars and other black holes. As they feast, friction causes the material
spiraling into the black holes' to heat up, and they emit light that can be
detected by telescopes, turning them into “active galactic nuclei” (AGN).
-
- The most extreme
AGN are quasars, supermassive black holes that are billions of times heavier
than the sun and shed their gaseous cocoons with light blasts trillions of
times more luminous than the brightest stars.
-
- Because light
travels at a fixed speed through the vacuum of space, the deeper that
scientists look into the universe, the more remote light they intercept and the
further back in time they see. To spot the black hole the astronomers scanned
the sky with two infrared cameras the JWST's Mid-Infrared Instrument (MIRI) and
Near Infrared Camera and used the cameras' built-in spectrographs to break down
the light into its component frequencies.
-
- By deconstructing
these faint glimmers from the universe's earliest years, they found an
unexpected spike among the frequencies contained within the light, a key sign
that the hot material around a black hole was beaming out faint traces of light
across the universe.
-
- The Webb Space Telescope also spotted six
gigantic galaxies, each roughly the size of our own Milky Way, that formed at a
bafflingly fast pace, taking shape just 500 million years after the Big Bang.
-
- This group of
galaxies from the dawn of the universe
are so massive they shouldn't exist.
The six gargantuan galaxies, which contain almost as many stars as the
Milky Way despite forming only 500 to 700 million years after the Big Bang,
have been dubbed "universe breakers". If they're real, the discovery calls our
entire understanding of galaxy formation into question.
-
- Scientists don't
know exactly when the first clumps of stars began to merge into the beginnings
of the galaxies we see today, but cosmologists previously estimated that the
process began slowly taking shape within the first few hundred million years
after the Big Bang. Currently accepted theories suggest that 1 to 2 billion
years into the universe's life, these early protogalaxies reached adolescence
forming into dwarf galaxies that began devouring each other to grow into ones
like our own.
-
- Because light
travels at a fixed speed through the vacuum of space, the deeper we look into
the universe, the more remote light we intercept and the further back in time
we see. JWST is peering roughly 13.5 billion years into
the past, the astronomers found that enormous galaxies had already burst into
life very quickly after the Big Bang, when the universe was just 3% of its
current age.
-
- The galaxies are so
massive, they are in tension with 99 percent of the models for cosmology. This means that either the models need to be
altered, or scientific understanding of galaxy formation requires a fundamental
rethink.
-
- Right now, all
evidence points to these celestial objects being galaxies, but the astronomers
haven't ruled out that some of them could be enormous quasars or supermassive
black holes.
-
- Previous imaging of
the early universe by the Hubble Space Telescope didn't detect the giant
galaxies, but JWST is about 100 times more powerful than Hubble.
-
- The $10 billion JWST
launched to a gravitationally stable location beyond the moon's orbit, a
Lagrange point, in December 2021. The space observatory was designed to read
the earliest chapters of the universe's history in its faintest glimmers of
light, which have been stretched to infrared frequencies from billions of years
of travel across the expanding fabric of space-time.
-
- The next step will
be to take a spectrum image of the giant galaxies, providing them with accurate
distances and a better idea of the chemical makeup of the beginning of the universe.
-
-
January 5, 2023 THE FIRST
STARS? 4306
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