Friday, March 10, 2023

3911 - COSMIC WEB - new pictures of the universe?

 

-   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. 

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-   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.

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-    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.

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-   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.

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-   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.

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-   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.

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-    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.

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-    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.

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-    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.

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-    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.

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-    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.

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-   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.

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-    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.

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-   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.

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-    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.

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-   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.

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-     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.

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-   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.

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                   March 9, 2023        COSMIC  WEB  -    new pictures of the universe?              3911                                                                                                                         

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--------------------- ---  Friday, March 10, 2023  ---------------------------

 

 

 

 

           

 

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