Tuesday, February 7, 2023

3865 - COSMOLOGY - how it all got started?

 

-  3865 -   COSMOLOGY  -  how it all got started?     The James Webb Space Telescope observed a galaxy that existed about 325 million years after the Big Bang this past summer, 2021. This established a new record for the earliest galaxy ever observed. However, the JWST can only observe the brightest galaxies from this epoch, while arrays like HERA and CHIME continue to probe the “darker” regions of the early Universe.


---------------  3865  -   COSMOLOGY  -  how it all got started?

-    The cosmic “Dark Ages,”  lasted from roughly 370,000 to 1 billion years after the Big Bang, where the Universe was shrouded with light-obscuring neutral hydrogen. The first stars and galaxies formed during this period (100 to 500 million years), slowly dispelling the “darkness.” This period is known as the “Epoch of Reionization”, or “Cosmic Dawn”.

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-    The “Hydrogen Epoch of Reionization Array” (HERA), is a radio telescope dedicated to observing the large-scale structure of the cosmos during and before thi period of the Epoch of Reionization.  It is located in the Karoo desert in South Africa.

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-    Based on current cosmological models, the Universe began 13,800,000,000 years ago with the Big Bang, which produced a flurry of energy and elementary particles that slowly cooled to create the first protons and electrons which combined to form the first hydrogen and helium atoms.

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-   The leftover “relic radiation” is observable today in the form of the “Cosmic Microwave Background” (CMB).  The missions like the COBE, WMAP, and Planck, have mapped the faint variations in temperature that existed 380,000 years after the Big Bang.

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-     Hubble has observed galaxies as they existed roughly 1 billion years after the Big Bang  (13 billion years ago). This has led to a greater understanding of how galaxies evolved and the possible role of Dark Matter and Dark Energy in the process.

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-    However, there is a gap between these observations of the CMB and early galaxies: the “Dark Ages” ( 370,000 to 1 billion years after the Big Bang). This epoch cannot be studied with conventional telescopes because photons in this period were either part of the CMB or those released by neutral hydrogen atoms, the 21-centimeter hydrogen line.

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-     As the first stars and galaxies gradually formed, the intense radiation they emitted reionized much of the surrounding Universe. This led to this Epoch of Reionization, where neutral hydrogen began to form clouds of plasma of free electrons and protons.

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-    To map these bubbles, HERA, and other sophisticated radio telescopes were created to observe the hydrogen line (which has a frequency of 1,420 megahertz). This wavelength of light is one that neutral hydrogen absorbs and emits, but ionized hydrogen does not.

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-    Since the Epoch of Reionization, this radiation has been redshifted by the expansion of the Universe to a wavelength of about 2 meters (6 feet). HERA’s simple antennas, built from chicken wire, PVC pipe, and telephone poles, are 14 meters (46 feet) in diameter, allowing them to focus this radiation onto detectors.

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-   The backend is consisting of a supercomputer and machine learning algorithms performing advanced data analysis. This map could track galactic evolution from the very early Universe to today.

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-    The results showed that the earliest stars, which may have formed around 200 million years after the Big Bang, contained few other elements than hydrogen and helium. The finding is consistent with accepted models of stellar evolution, which state that metals from lithium to uranium formed within the first generation of stars.

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-    When these stars collapsed after a comparatively short lifespan (hundreds of millions of years rather than billions), these metals were shed with the stars’ outer layers, seeding the Universe with metals that became part of subsequent generations of stars.

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-    Astronomers are interested in the atomic composition of these early stars since this would show how long they took to heat the intergalactic medium (IGM) and cause reionization to occur.

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-   A key element is high-energy radiation (primarily X-rays) produced by binary stars once one of them goes supernova, collapsing into a black hole or neutron star and eventually consuming their companion. Since the earliest stars had very few heavy elements (low metallicity), they would not have heated the surrounding region much and produced fewer X-rays.

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-   The absence of the signal largely rules out the “Cold Reionization” theory, which posits that reionization had a colder starting point. Instead, the HERA researchers suspect that the X-rays from binary stars heated the intergalactic medium (IGM) first.

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-    Even before reionization and by as late as 450 million years after the Big Bang, the gas between galaxies must have been heated by X-rays. These came from binary systems where one star loses mass to a companion black hole.  Those stars must have been very low ‘metallicity,’ very few elements other than hydrogen and helium in comparison to our sun.

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-    These findings agree with the preliminary results from the first analysis of HERA 2022 data that hinted that alternative theories like “Cold Reionization” were unlikely. These results were based on 18 nights of observation by Phase I of the HERA project (about 40 antennas) and were the most sensitive observations of the early Universe to date.

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-   This latest is based on 94 nights of Phase I observations (between 2017 and 2018) and demonstrates how the HERA team has improved the array’s sensitivity.

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-    This includes a 2.1-factor increase for light emitted about 650 million years after the Big Bang (a redshift value (z) of 7.9) and a 2.6-factor increase for radiation emitted about 450 million years after the Big Bang (z=10.4).

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-   These latest observations are the best evidence we have of heating of the intergalactic medium by early galaxies. Astronomers hope to construct a 3D map of the ionized and neutral hydrogen bubbles from 200 million to 1 billion years after the Big Bang.  There is always more to learn!

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            February 7, 2023           COSMOLOGY  -  how it all got started?           3865                                                                                                                           

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--------------------- ---  Tuesday, February 7, 2023  ---------------------------

 

 

 

 

         

 

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