- 3911 - COSMIC WEB - new pictures of the universe? The universe is permeated by a vast, invisible web, its tendrils weaving through space. But despite organizing the matter we see in space, this dark web is invisible. That's because it is made up of dark matter, which exerts a gravitational pull but emits no light.
------------ 3911 - COSMIC WEB - new pictures of the universe?
- For the
first time, researchers have illuminated some of the darkest corners of the
universe so we can make out the cosmic web interconnecting the galaxies
throughout space.
-
- Going back
in time, the universe was hotter, smaller and denser than it is now. There wasn't much variation in density from
place to place. In the young universe,
no matter where you went, things were pretty much the same.
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- But there
were tiny, random differences in density. Those nuggets had slightly more
gravitational pull than their surrounding neighborhood, and so matter tended to
flow into them. Growing bigger in this way, they developed an even stronger
gravitational influence, pulling more matter in, causing them to be bigger, and
so on and so on for billions of years. Simultaneously, as the nuggets grew, the
spaces between them emptied out.
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- Over the
course of cosmic time the dense patches grew to become the first stars,
galaxies and clusters, while the spaces between them became the great cosmic
voids.
-
- Now, 13.8
billion years into this massive construction job matter is still streaming out
of the voids, joining groups of galaxies that are flowing into dense, rich
clusters. What we have today is a vast, complex network of filaments of matter
that we call the cosmic web.
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- The vast
majority of matter in our universe is dark; that is it does not interact with
light or with any of the "normal" matter that we see as stars and gas
clouds and other interesting things. As a result, much of the cosmic web is
completely invisible to us.
-
- Like a lighthouse
on a distant, black seashore, the stars and galaxies tell us where the hidden
dark matter lurks, giving us a ghostly outline of the cosmic web's true
structure.
-
- With this
biased view, we can easily see the clusters.
We know for sure there's a tremendous amount of dark matter in those
structures, since you need a lot of gravitational forces to pool together that
many galaxies.
-
- And on the
opposite end of the spectrum, we can easily spot the voids; they are the places
where all the matter isn't. Because there are no galaxies to illuminate these
spaces, we know that they are, by and large, truly empty.
-
- But the
grandeur of the cosmic web lies in the delicate lines of the filaments
themselves. Stretching for millions of light-years, these thin tendrils of
galaxies act like great cosmic freeways crossing black voids, connecting bright
urban clusters.
-
- Those
filaments in the cosmic web are the hardest part of the web to study. They have
some galaxies but not a lot. Recently astronomers have cataloged of so-called luminous red galaxies
(LRGs) from the Baryon Oscillation Spectroscopic Survey (BOSS) survey. LRGs are
massive beasts of galaxies, and they tend to sit in the centers of dense blobs of
dark matter. And if the LRGs sit in the densest regions, then lines connecting
them should be made of the more delicate filaments.
-
- But staring
at the space between two LRGs isn't going to be productive; there isn't a lot
of stuff there. So, the team took thousands of pairs of LRGs, realigned them
and stacked them on top of each other to make a composite image.
-
- Using this
stacked image, the scientists counted all the galaxies that they could see,
adding up their total light contribution. This allowed researchers to measure
how much normal matter made up the filaments between the LRGs. Next, the
researchers looked at the galaxies behind the filaments, and specifically, at
their shapes.
-
- As light
from those background galaxies pierced the intervening filaments, the gravity
from the dark matter in those filaments gently nudged the light, ever so
slightly shifting the images of those galaxies. By measuring the amount of
shifting, called "shear" , the team was able to estimate the amount
of dark matter in the filaments.
-
- That measure
lined up with theoretical predictions and point to the existence of dark
matter. They confirmed that the filaments weren't entirely dark. For every 351
suns' worth of mass in the filaments, there was 1 suns' worth of light output.
-
- This is first
evidence of shockwaves rippling through the "cosmic web," a massive
network of interweaving filaments that represents the largest structure in the
universe. The discovery represents tantalizing evidence of magnetic fields
weaving through the gas, dust, and dark matter tendrils which link galaxies
together.
-
- Scientists
first began to think that on the largest scales, the universe is ordered in a
web-like pattern with filaments that cross vast voids in space and pull
galaxies into clusters in the 1960s.
Astronomers have since mapped the cosmic web with actual observations in
the process answering questions about its structure.
-
- One element
has remained frustratingly shrouded in mystery, however: The magnetic fields
that may run throughout the cosmic web.
Magnetic fields pervade the universe from planets and stars to the
largest spaces in-between galaxies.
However, many aspects of cosmic magnetism are not yet fully understood,
especially at the scales seen in the cosmic web.
-
- When matter
merges in the universe, it produces a shockwave that accelerates particles, and
this amplifies intergalactic magnetic fields. In the cosmic web, gravity draws
filaments together and this should generate shockwaves that make the magnetic
field in the web stronger. As a result, these fields should emit a radio wave
glow that should be observable with radio telescopes here on Earth.
-
- By
stacking data and all-sky radio maps from the Global Magneto-Ionic Medium
Survey, the Planck Legacy Archive, the Owens Valley Long Wavelength Array and
the Murchison Widefield Array over the known clusters and filaments in the
cosmic web, the astronomers spotted these radio emissions for the first time.
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- This led
them to search for a different signal type, polarized radio light, which they
reasoned would be blighted by less background noise. Polarization occurs when
light waves pass through a filter that only allows waves with a specific
orientation to emerge. After this filtering, the light has been polarized.
-
- By stacking
their data, the team ensured the faint radio wave signal was strengthened. This
resulted in the creation of the first simulation of the cosmic web to include
predictions of the polarized radio light from the cosmic shockwaves.
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-
Understanding the magnetic fields lit up in radio waves by these
shockwaves could now be used to expand and refine our theories on how the
universe expands. The results also have the potential to assist astronomers to
solve the mysterious origins of cosmic magnetism.
-
March 9, 2023 COSMIC
WEB - new pictures of the universe? 3911
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--------------------- --- Friday, March 10, 2023
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