- 4580 - LARGER GALAXY STRUCTURES? - The Milky Way might be part of an even larger structure than Laniakea. If you want to pinpoint your place in the Universe, start with your cosmic address. You live on Earth->Solar System->Milky Way Galaxy->Local Cluster->Virgo Cluster->Virgo Supercluster->Laniakea.
----------------------------------- 4580
- LARGER GALAXY STRUCTURES?
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- Thanks to new deep sky surveys, astronomers
now think all above places are part of an even bigger cosmic structure in the
“neighborhood” called the “Shapley Concentration”.
-
- Astronomers refer to the Shapley
Concentration as a “basin of attraction”. That’s a region loaded with mass that
acts as an “attractor”. It’s a region containing many clusters and groups of
galaxies and comprises the greatest concentration of matter in the local
Universe. All those galaxies, plus dark matter, lend their gravitational
influence to the Concentration. There are many of these basins in the Universe,
including Laniakea.
-
- Astronomers measured the motions of some
56,000 galaxies to understand these basins and their distribution in
space. Our universe is like a giant web,
with galaxies lying along filaments and clustering at nodes where gravitational
forces pull them together. Just as
water flows within watersheds, galaxies flow within cosmic basins of
attraction. The discovery of these larger basins could fundamentally change our
understanding of cosmic structure.
-
- “Redshift” surveys revealed a possible
shift in the size and scale of our local galactic basin of attraction. We
already know that we “live” in Laniakea, which is about 500 million light-years
across. However, the motions of other clusters indicate there’s a larger
“attractor” directing the cluster flow.
-
- The Cosmic Flows data suggest that we could
be part of the “Shapley Concentration”, which could be 10 times the volume of
Laniakea. It’s about half the volume of the largest structure in space, known
as “the Great Wall”, which is a string of galaxies stretching across 1.4 billion light-years.
-
- The “2dF Galaxy Redshift Survey” contains the structure known as the
"Sloan Great Wall". The Shapley Concentration was first observed by
astronomer Harlow Shapley in the 1930s as a “cloud” in the constellation
Centaurus. This supercluster appears along the direction of motion of the Local
Group of galaxies (where we live).
-
- Scientists speculated that this could be
influencing our galaxy’s peculiar motion.
The Virgo Supercluster (and the Local Group and Milky Way Galaxy)
appears to be moving toward the Shapley Concentration.
-
- Where do these basins of attraction come
from? In one sense, they’re as old as the Universe and its cosmic web of
matter. The seeds for the web and those basins of attraction were planted some
13.8 billion years ago.
-
- After the Big Bang, the infant Universe was
in a hot dense state. As it expanded and cooled, the density of matter started
to fluctuate. There were tiny differences in those density fluctuations. Think
of them as the earliest “seeds” of galaxies, galaxy clusters, and even vaster
structures that we see in today’s Universe.
-
- As astronomers survey the sky, they find
evidence for all those different structures. Now, they have to explain them.
The idea that the Shapley Concentration is the large basin that our Laniakea
belongs to means that current cosmological models don’t quite explain its
existence.
-
- Our cosmic surveys may not yet be large
enough to map the full extent of these immense basins. The main actor in all these galaxies,
clusters, and superclusters, is gravity. The more mass, the more gravity
influences motions and matter distribution.
-
- These basins of attraction exert a sort of
“tug of war” on galaxies that lie between them. That influences their motions.
In particular, redshift surveys will map the radial motion (along the line of
sight), velocities (how fast they’re moving), and other related motions. By
mapping the velocities of galaxies throughout our local Universe, they can
define the region of space where each supercluster dominates.
-
- Astronomers aren’t mapping just the luminous
material in galaxies. They also have to take into account the inferred
existence of dark matter. There are other complications as well. Not all galaxies are the same. They differ in their shapes and matter
density. Astronomers can get around this by measuring something called “galaxy
peculiar velocity”. That’s the difference between its actual velocity and the
expected “Hubble flow” velocity (which reflects gravitational interactions
between galaxies).
-
- The results of these surveys should provide
ever more precise 3D maps of these regions of space. That includes their
structures as well as their motions and velocities. Those maps, in turn, should
give greater insight into the distribution of all matter (including cold dark
matter) throughout the Universe.
-
-
October 19, 2024 LARGER
GALAXY STRUCTURES? 4580
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------ “Jim Detrick” -----------
--------------------- --- Sunday, October 20,
2024
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