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How the Universe Evolved
Poziom:
Temat: Nauka i technologia
Galaxies once were regarded as island universes,
isolated realms of gas, dust, and billions
of stars that were separated by distances
unimaginably vast.
But no galaxy is an island. In fact, galaxies
prefer company. The gravitational pull of
a large massive galaxy attracts like-sized
and smaller neighbors
Galaxies may gather in modest groupings like
these or congregate by the hundreds in enormous
clusters. This is Abell 1689, one of the largest
galaxy clusters known. This view spans two
million light years, or about the distance
between our own Milky Way galaxy and the nearest
big spiral.
Into this space, Abell 1689 packs more than
five hundred galaxies. As astronomers mapped
nearby galaxy clusters, a more complete picture
of cosmic structure emerged. Galaxy clusters
gather in superclusters, and overlapping superclusters
formed chains and filaments spanning huge
swaths of the sky.
Welcome to the cosmic web. This all sky map
shows structures created by more than a million
nearby galaxies.
Deeper studies show that this pattern continues
to even greater distances. The cosmic web
appears to be the backbone of our universe.
The universe came into being thirteen point
seven billion years ago. About four hundred
thousand years later, it had cooled enough
to form the first atoms.
The event created a sudden pulse of light
that astronomers now measure as the cosmic
microwave background.
Then, the universe went dark, for millions
of years. Eventually, hydrogen gas cooled
enough to collapse and form the first stars.
These stars not only re-illuminated the universe,
they became the seeds of all future cosmic
structure. The James Webb Space Telescope
may be able to see clusters of these first
stars. It may even catch a few of them dying
in supernova explosions.
Either the first stars or their progeny gather
into the first galaxies. These were small
gas rich dwarfs, nothing as grand as the big
galaxies we see today, but they were the building
blocks of modern galaxies.
As the dwarf galaxies form, collide, and merge
into bigger galaxies, the cosmic web begins
to take shape.
