Monday, May 1, 2023

3979 - UNIVERSE - first light?

 

-   3979  -  UNIVERSE  -   first light?    By measuring the Cosmic Microwave Background for redshift and comparing these to local distance measurements (using variable stars and supernovae), astronomers have sought to measure the rate at which the universe is expanding.

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-----------------------  3979  -   UNIVERSE  -  first light?

-    In the 1960s, astronomers began noticing a pervasive microwave background visible in all directions. This became known as the “Cosmic Microwave Background” (CMB), the existence of this relic radiation confirmed the Big Bang theory that all matter was condensed onto a single point of infinite density and extreme heat that began expanding 13.8 billion years ago.

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-   Scientists observed that the rotational curves of galaxies were much higher than their visible mass suggested. This meant that either Einstein's Theory of General Relativity was wrong or the universe was filled with a mysterious, invisible mass.

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-  Astronomers are using improved measurements of parameters that describe the very early universe by monitoring the light that emerged during "Cosmic Dawn" (when the universe was only 380,000 years old), which is visible today as the CMB.

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-   According to the cosmological model,the “Lambda Cold Dark Matter (LCDM)”,  Dark Matter accounts for 85% of the mass in the cosmos. Unfortunately, it doesn't interact with normal ("luminous") matter via electroweak or strong nuclear forces, only with gravity (the weakest of the fundamental forces).

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-    To track down this illusive and "invisible" mass, the ACT collaboration uses the “Atacama Cosmology Telescope” (ACT), a custom-built six-meter (20-foot) millimeter-wave telescope located in northern Chile.

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-   Astronomers used data from the ACT's Data Release 6 (DR6), which consisted of five seasons of CMB temperature and polarization observations. These light readings were essentially used to backlight all of the matter between the present day and the Big Bang ( 13.8 billion years ago).

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-    It's a bit like silhouetting, but instead of just having black in the silhouette, you have texture and lumps of dark matter, as if the light were streaming through a fabric curtain that had lots of knots and bumps in it. The CMB image is a snapshot of what the universe was like in a single epoch, about 13 billion years ago, and now this is giving us the information about all the epochs since.

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-    The full-sky image is based on data collected by the “Wilkinson Microwave Anisotropy Probe” (WMAP) between 2001 and 2003. This mission (which remained in operation until 2010) built on the previous work by the “Cosmic Background Explorer” (COBE), which collected data on the CMB from 1989 to 1993.

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-   Then came the ESA's “Planck” satellite, which measured the CMB from 2009 to 2013 to map tiny temperature fluctuations. The increasingly accurate maps that resulted have provided insight into the evolution of the cosmos by showing what its initial conditions were.

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-    This latest map has taken that research a step further by using it to measure how the structure of matter has evolved since, 85% of which is Dark Matter.

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-     To visualize the presence and distribution of this mysterious mass, the research team examined how its gravity affected the curvature of spacetime between the CMB and Earth. This effectively showed how large collections of mass (both visible and invisible) altered the path its light followed as it traveled for billions of light-years distance (and billions of years time) to reach us.

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-     The astronomers tracked how the gravitational pull of massive dark matter structures can warp the CMB on its 14-billion-year journey to us, just as antique, lumpy windows bend and distort what we can see through them. The resulting map revealed the "scaffold" of Dark Matter that holds visible matter and surrounds and connects galaxies and galaxy clusters.

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-    This led to the universe's large-scale structure, referred to as the "Cosmic Web". This map breaks with convention by measuring the distribution of matter in our universe, not in terms of light but in terms of mass.

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-   This is stunning evidence that we understand the story of how structure in our universe formed over billions of years, from just after the Big Bang to today. Remarkably, 80% of the mass in the universe is invisible. By mapping the dark matter distribution across the sky to the largest distances, our ACT lensing measurements allow us to clearly see this invisible world.

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-    It provides measurements that show that both the 'lumpiness' of the universe, and the rate at which it is growing after 14 billion years of evolution, are just what you'd expect from our standard model of cosmology based on Einstein's theory of gravity.

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-    These results could also provide new insight into the so-called "Crisis in Cosmology," where light measurements using the CMB vs. local stars produce different values. Also known as the "Hubble Tension," this disparity suggests that Dark Matter was not "lumpy" enough and that the standard model of cosmology (LCDM) may be incorrect.

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-    However, the ACT team's latest results precisely assessed the size and distribution of these lumps and determined that they were perfectly consistent with the LCDM model.

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-    The CMB is famous already for its unparalleled measurements of the primordial state of the universe, so these lensing maps, describing its subsequent evolution, are almost an embarrassment of riches. We now have a second, very primordial map of the universe.

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-    We have an extraordinary opportunity to use these different data sets together. This map includes all of the dark matter, going back to the Big Bang, and the other maps are looking back about 9 billion years, giving us a layer that is much closer to us. We can compare the two to learn about the growth of structures in the universe.  The two approaches are getting different measurements.

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-    While the ACT was decommissioned in September 2022 (after 15 years in operation), the data it gathered still inspire new research and breakthroughs. More papers presenting results from the final set of observations in the DR6 are expected soon, and the Simons Observatory will conduct future observations from the same sight.

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-     These will be done using a new telescope scheduled to begin operations in 2024 that will be capable of mapping the sky almost ten times as fast as the ACT. Perhaps we can look forward to all-sky surveys that map the distribution of Dark Matter going back to the beginning of the cosmos.

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                   April 30, 2023            UNIVERSE  -  first light?                3979                                                                                                                         

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