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The Big Bang
0.000000000000000000000000000000000001 seconds after the Big
Bang
The universe began with a vast explosion that generated space
and time, and created all the matter and energy in the
universe. Exactly what triggered this sudden expansion remains
a mystery. Astronomers believe it involved a runaway process
called "inflation," in which a peculiar type of energy that
existed in the vacuum of space was suddenly mobilized. The
inflationary expansion ended only when this energy was
transformed into more familiar forms of matter and energy.
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Ultimate High-Energy Lab
1 second after the big bang
After inflation ended in the first tiny fraction of a second,
the universe continued to expand but not nearly so quickly. As
the universe cooled, the most basic forces in nature emerged:
first gravity, then the strong force, which holds nuclei of
atoms together, followed by the weak and electromagnetic
forces. In its first second of existence, the universe was
made up of fundamental particles, including quarks, electrons,
photons, and neutrinos. Protons and neutrons then began to
form.
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Basic Elements Form
3 minutes after the big bang
In the next few minutes, the universe as we know it took
shape. Already incomprehensibly large, its protons and
neutrons came together to form the nuclei of simple elements.
That the universe remains largely made up of these
elements—hydrogen and helium—is considered strong
evidence of the validity of the big-bang model.
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From Hot to Cold
500,000 years after the big bang
For the next 300,000 to 500,000 years or so, the universe
remained an enormous cloud of hot expanding gas. When this gas
had cooled to a critical threshold, electrons were able to
combine with hydrogen and helium nuclei. Photons no longer
scattered, but rushed outward. We can still see the photons
emitted from this period, but time and distance have shifted
them into microwave wavelengths. Today, this cosmic microwave
background radiation gives astronomers a window onto the early
universe.
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Birth of Stars and Galaxies
1,000,000,000 years after the big bang
As time moved forward, the pull of gravity exerted its
influence on the early universe. It amplified slight
irregularities in the density of the primordial gas. Even as
the universe as a whole continued to expand, pockets of gas
became more and more dense. Stars ignited within these
pockets. Groups of stars then became the earliest galaxies.
Modern telescopes can detect these primordial galaxies as they
appeared when the universe was only one billion years old,
just 7 percent of its present age.
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The Era of Quasars
3,000,000,000 years after the big bang
From one billion to three billion years after the big bang
many smaller galaxies merged into larger ones, forming an
array of shapes resembling spirals and spheres (known as
elliptical galaxies). Often the merger was so violent that
stars and gas collapsed into a common center, becoming so
dense they formed gigantic black holes. The gas flowing into
these black holes became hot enough to glow brightly before it
disappeared. The light of these "quasars" can be seen across
the depths of the universe.
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Supernova 9933
6,000,000,000 years after the big bang
Within galaxies, as stars were being born, others died...often
in enormous cataclysmic explosions. These explosions, called
supernovae, are important to the evolution of galaxies because
they distribute all the common elements such as oxygen,
carbon, nitrogen, calcium, and iron into interstellar space.
Explosions of especially massive stars also create and
distribute heavier elements such as gold, silver, lead, and
uranium. The supernova pictured here is of a smaller type,
used by astronomers to determine distance. This one appears to
us now as it looked when the universe was about five billion
years old.
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Birth of the Sun
5,000,000,000 years before the present
The sun formed within a cloud of gas in a spiral arm of the
Milky Way galaxy. A vast disk of gas and debris that swirled
around this new star coalesced into planets, moons, and
asteroids.
The image on the left, from the Hubble Space Telescope, shows
a star in the throes of birth. Powerful jets of radiation roar
out of its poles, lighting up the surrounding environment.
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Galaxies Collide
3,000,000,000 years in the future
Astronomers estimate that in about three billion years, our
Milky Way galaxy will be swallowed up by one of its nearest
neighbors, a large galaxy named Andromeda that lies 2.2
million light-years away. Depending on their pathways, these
two galaxies will either merge into a single gigantic galaxy
or rip each other apart, sending millions of stars like our
sun hurling into space. One such titanic collision involving
four galaxies, 300 million light-years away, is pictured at
left.
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Galaxies Disappear
100,000,000,000 years in the future
If recent observations of cosmic acceleration are correct,
then the "vacuum energy" that is emerging in the universe will
continue to overtake the pull of gravity from matter. This
means that, in the future, gravitationally bound clusters of
galaxies will survive but galaxies in general will fly ever
more rapidly apart. Eventually our nearest unbound neighbors
will be so far away that they will no longer be seen, even
with big telescopes. But this will be so far in the future
that our sun will have long since burned out and our Earth
died with it.
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Stellar Era Ends
1,000,000,000,000 years in the future
During this era, which will last from 100 billion years to one
trillion years after the big bang (and is the era we are
currently in), most of the energy generated by the universe
will be in the form of stars burning hydrogen and other
elements in their cores. This long period will give way to an
even longer, lingering death for our universe.
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The Degenerate Era
10,000,000,000,000,000,000,000,
000,000,000,000,000 years in the future
This era extends to ten trillion trillion trillion years after
the big bang. Most of the mass that we can currently see in
the universe will be contained in stars that have blown up and
collapsed into black holes and neutron stars. Or it will be
locked up in brown dwarfs and planets that never triggered
nuclear fusion, or in stars that withered into white dwarfs.
With stars no longer actively burning, energy in this era is
generated through proton decay and particle annihilation.
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The Black Hole Era
10,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000 years in the future
This era extends to ten thousand trillion trillion trillion
trillion trillion trillion trillion trillion years after the
big bang. After the epoch of proton decay, the only star-like
objects remaining are black holes of widely varying masses.
Their energy is steadily evaporating.
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The Dark Era
>10,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000,000,000,000,000,000,000,
000,000,000 years in the future
At this late stage, protons will have decayed and black holes
will have almost completely evaporated. Only the byproducts of
these processes remain: mostly neutrinos, electrons,
positrons, and photons of enormous wavelengths. For all
intents and purposes, the universe as we know it will have
come to an end.
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Images: (1-5) From a simulation of the Formation of Galaxies and
Large Scale Structure by Michael Norman, Brian O'Shea and Greg
Bryan, Grand Challenge Cosmology Consortium (GC3), and visualized by
Donna Cox, Stuart Levy, Robert Patterson, NCSA/UIUC; (6,8,9,11)
STScI/AURA/NASA; (7) High Z; (10,12) NOVA/NASA.
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