Astronomers are always looking for the “most
distant” galaxies, the “most energetic”
stellar explosions and the “most massive”
stars.
But what about the biggest cosmic walls?
Hello!
I’m Ian O’Neill, space producer for Discovery
News, and I want you to imagine the biggest
collection of galaxies possible.
Now double it.
No, triple it.
Can you see it?
Yep, that’s a galactic wall.
Well, OK, these aren’t walls of bricks and
mortar; they’re walls of galaxies cemented
together by dark matter.
They are the biggest structures in the universe
that we know of.
And.
They.
Are.
HUGE.
But what are they exactly?
Well, nearly 14 billion years ago, our universe
exploded from a single point, spewing matter
and energy to form the rapidly expanding universe
we know and love.
All the matter in the universe splattered
and condensed into long web-like filaments
of dark matter, along which galaxies gravitationally
attached themselves.
As the universe cooled and matured, a 3-dimensional
web of galaxies formed -- composed of both
these long filaments and vast bubble-like
voids.
Along these filaments, dense superclusters
of galaxies settled -- this is what we call
“galactic walls.”
And perhaps the most famous galactic wall
is the Sloan Great Wall that was discovered
by the Sloan Digital Sky Survey -- or SDSS
-- in 2003.
It’s basically a huge collection of galaxies
about 1 billion light-years from Earth, spanning
over 1.4 billion light-years across (it therefore
takes light 1.4 billion years to travel from
one end to the other).
Though impressive, the Sloan Great Wall is
no longer the biggest, but it remains the
most famous.
Since 2003, bigger galaxy walls have been
detected, but this year, the biggest wall
of all has been claimed.
When studying a collection of distant galaxies
between 4.5 and 6.4 billion light-years away,
astronomers realized that over 800 of them
occupy the same cosmic filament, a volume
ten times that of the Sloan Great Wall.
They called it the BOSS Great Wall -- after
the Baryon Oscillation Spectroscopic Survey,
a project also run by the SDSS.
BOSS is designed to study the distribution
of galaxies throughout the cosmos, in an effort
to understand how fast the universe is expanding
and how galaxies move in relation to one another.
Though impressive, these Great Walls may not
actually be the greatest of them all.
For starters, records are made to be broken,
and bigger walls could be discovered in the
future as surveys get more and more sensitive.
Also, there’s a large swathe of sky BEHIND
our galaxy called the “Zone of Avoidance”
that astronomers cannot see -- it’s a region
of sky the Milky Way’s core and disk is
blocking from view.
So there could be the mother of all walls
that we’ll never observe.
So why do we care about these huge walls of
galaxies besides the fact we love big things
in space and we love breaking records?
Well, according to the “cosmological principle,”
all matter in the universe, when viewed on
a large enough scale, should appear more or
less uniform and the largest structures shouldn’t
exceed 1.2 billion light-years across.
This is based on a mathematical theory put
forth by none other than Isaac Newton.
A possible galactic wall measuring over 1.2
billion light years across could mean that
our understanding of the universe is incomplete
or incorrect.
And there are clues that there are even bigger
structures out there.
Speaking of huge cosmic structures, there’s
a mysterious cold spot imprinted in the cosmic
microwave background, watch my recent DNews
video about what this discovery could mean:
So what do you think is going on?
Is our understanding of the universe flawed?
Let us know in the comments, and don’t forget
to like this video and subscribe for a new
episode of DNews every day.
