Saturday, June 17, 2023

4057 - EARLIEST GALAXIES - was this the beginning?

 

-    4057  -   EARLIEST  GALAXIES  -   was this the beginning?   The James Webb Telescope (JWST or Webb) has unveiled hundreds of ancient galaxies that could be among the first members of the universe.  As early as 600 million years after the Big Bang, these very young galaxies had complex structures and clusters of star formation.


---------------   4057   -    EARLIEST  GALAXIES  -   was this the beginning?

-      JWST has gathered observations from two tiny patches in the sky.   One in the Ursa Minor constellation and another in the direction of the Fornax cluster. Within this region were over 700 newly discovered young galaxies that reveal with the universe looked like in its earliest beginning.

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-    If you took the whole universe and shrunk it down to a two hour movie, you are seeing the first five minutes of the movie.  These are the galaxies that are starting the process of making the elements and the complexity that we see in the world around us today.

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-    In those five minutes alone, which marks the universe to be between 370 million and 650 million years old, they found 717 young galaxies  with all of them already spanning thousands of light-years, sporting complex structures, and birthing stars in multiple clusters.

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-    Previously, the earliest galaxies we could see just looked like little smudges. And yet those smudges represent millions or even billions of stars at the beginning of the universe.

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-     Despite previous scrutiny, 93% of the newfound galaxies that Webb spotted  had never been seen before.    Precisely how that chaotic, very dusty environment cleared up to become the transparent cosmos we see today has long been debated.-

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-    A leading theory is that this phase of evolution of the universe, called the Epoch of Reionization, occurred some 400,000 years after the Big Bang, when the first generation of stars, thought to be 30 to 300 times our sun's mass and millions of times more bright, formed and flooded the opaque universe with its first light.

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-    That ultraviolet starlight reionized the universe by splitting its abundant hydrogen atoms into protons and electrons, a process that lasted until one billion years after the Big Bang. However, outflows from supermassive black holes, similar to the one that resides in the heart of our Milky Way, could have triggered the escape of ultraviolet radiation from galaxies and thus played a more important role in cosmic evolution than previously thought.

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-    Astronomers are studying galaxies that existed between 500 to 850 million years after the Big Bang, or between five to eight minutes of the two-hour movie describing the universe, thinks they have an answer to the long-standing question.

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-    Galaxies in the very early universe were just far more chaotic in general in how they formed stars.  One in six galaxies at the time showed extreme line emissions in the galaxy's spectra, a feature that atoms ionized by starlight radiate when they have cooled down and combined with other molecules.

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-   Those emission lines are evidence that early galaxies were actively birthing stars, which then pumped "torrents of ultraviolet photons" into their respective galaxies. This way, the universe's early stars became the main drivers of cosmic reionization.

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-    These extreme emission lines are actually relatively common in the very early universe.  Almost every single galaxy that we are finding shows these unusually strong emission line signatures indicating intense recent star formation.  These early galaxies were very good at creating hot, massive stars.

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-    All of a sudden you would have tens of suns worth of solar masses being assembled all at once in these early galaxies.   That's really important for our understanding of how reionization happened because these hot massive stars were very efficient producers of these ultraviolet photons that we needed in order to ionize all the hydrogen in the early universe.

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-    Shortly after the Big Bang, the universe was a dark and mysterious place.   The gas between stars and galaxies was opaque, so no light could shine through. As anyone who's ever looked through a telescope knows, that's no longer the case, since we can see celestial objects all throughout the universe from our vantage point here on Earth. But what caused the change in opacity?

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-    This was back in time at galaxies from the end of the “Era of Reionization”, a dramatic period in the universe's history in which gas was heated, cooled and then reionized,  given an electrical charge once again.

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-    More than 13 billion years ago, during the Era of Reionization, the universe was a very different place. The gas between galaxies was largely opaque to energetic light, making it difficult to observe young galaxies. What allowed the universe to become completely ionized, leading to the "clear" conditions detected in much of the universe today?

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-     Looking at those early galaxies, which existed just 900 million years after the Big Bang, astronomers saw that most of the gas in the universe was somewhere between opaque and transparent. But directly around the galaxies, everything was clear.

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-    We are seeing galaxies reionize the gas around them.  Imagine that each of these young galaxies was surrounded by a balloon. Energy from newly forming stars reionized the gas inside that balloon. As the galaxies grew, the bubbles of reionized gas merged, creating even larger pockets of transparency. Eventually, they all combined to create a transparent universe.

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-    This phenomenon could be seen in action thanks to the illumination of a quasar, an extremely bright supermassive black hole. Turning Webb toward one particular quasar, the astronomers observed its light moving through the universe's gas, being absorbed by opaque gas in some areas and traveling through transparent gas in others.

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-    By illuminating gas along our line of sight, the quasar gives us extensive information about the composition and state of the gas.  Next, the team will more deeply research galaxies in five other areas of the sky that all have a central quasar, shedding more light on the opacity of the early universe.

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June 16,  2023      EARLIEST  GALAXIES  -   was this the beginning?           4057

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--------------------- ---  Saturday, June 17, 2023  ---------------------------------

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