-    4375  -  FARTHEST  GALAXIES  -   On a clear night, it might look like the stars above are distributed more or less evenly. But that isn't the case.   All stars are part of a gigantic cosmic web that links galaxies across the universe like threads of spider's silk, leaving large swaths of nothingness in between.  This massive cosmic highway stretches back nearly to the dawn of the universe.

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-    The James Webb Space Telescope discovered a massive, gassy tendril composed of 10 closely packed galaxies stretching over 3 million light-years.   This ancient filament of gas and stars may represent the oldest known thread of the cosmic web.

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-   The filament formed when the universe was young, 830,000,000 years after the Big Bang. It is anchored by an extremely bright celestial object with a supermassive black hole known as a quasar at its center.

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-    This bright black hole is the reason scientists discovered the tendril.  This is one of the earliest filament structures that people have ever found associated with a distant quasar.

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-    Black holes helped to form the cosmic web by acting as gravity wells to draw matter together, and occasionally by flinging it far away on "cosmic winds," which whip up around extremely active quasars. Gravity keeps these strands of stars and dust connected, even as the winds pull them across the universe.

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-   The filament will condense into a cluster of galaxies, similar to the Coma Cluster, which lies approximately 330 million light-years from Earth.   The main surprise is that these small faint galaxies had so much power, their cumulative radiation could transform the entire universe.

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-   This effect predicted by Albert Einstein over 100 years ago was to discover that small galaxies in the early cosmos packed a massive punch, shaping the entire universe when it was less than 1 billion years old.

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-    The galaxies resemble dwarf galaxies that exist today.   They played a vital role during a crucial stage of cosmic evolution that occurred between 500 and 900 million years after the Big Bang. These small galaxies also vastly outnumbered larger galaxies in the infant universe.  They supplied most of the energy needed for a process called “cosmic reionization”. Cosmic reionization was critical to the growth and progression of the universe.

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-    We're really talking about the global transformation of the entire universe.  The main surprise is that these small, faint galaxies had so much power, their cumulative radiation could transform the entire universe.

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-   Prior to around 380,000,000 years after the Big Bang happened, during a period called the “epoch of recombination”, the now 13.8 billion-year-old universe had been opaque and dark. This was because, in its dense and ultra-hot state, free electrons endlessly bounced around particles of light, photons.

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-    Later, during the “epoch of recombination” the universe had expanded and cooled enough to allow electrons to bond with protons and create the first atoms of hydrogen, the lightest and simplest element. This disappearance of free electrons meant photons were suddenly free to travel, and as a result, the "dark age" of the universe ended.

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-     The cosmos suddenly became transparent to light. This "first light" can be seen today in the form of a cosmic fossil that uniformly fills the universe called the "cosmic microwave background" or "CMB."

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-   Because electrons and protons have equal but opposite electric charges, these first atoms were electrically neutral, but they would soon undergo yet another transformation.

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-    After 400 million years, the first stars and galaxies formed during the “era of reionization”, neutral hydrogen, the predominant element in the universe, was transformed into charged particles. These particles are called ions. Ionization is caused by electrons absorbing photons and increasing their energy, breaking free from atoms.

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-    Inflation poses that the universe initially expanded far faster than the speed of light and grew from a subatomic size to a golf-ball size almost instantaneously.   Suspects for the radiation source behind reionization had included supermassive black holes feeding on gas from accretion disks surrounding them causing these regions to eject high-energy radiation.   The universe had large galaxies with masses in excess of 1 billion suns, and smaller galaxies with masses less than this.

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-   The JWST has spectroscopic capabilities in the infrared.  One of the reasons we built the JWST is to understand what happened during the epoch of reionization.  Even with the impressive infrared observing power of the JWST, spotting these dwarf galaxies wouldn't have been possible without the help of Albert Einstein, without the help of his 1915 theory of general relativity, and an effect on light it predicts.

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-    General relativity suggests all objects of mass warp the very fabric of space and time, which are, in truth, united as a single entity called "spacetime."   Our perception of gravity arises as a result of that curvature. The greater the mass of an object, the more "extreme" the curvature of spacetime is. Thus, the stronger its gravitational effects are.

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-    Not only does this curvature tell planets how to move in orbits around stars and, in turn, tell those stellar bodies how to orbit the supermassive black holes at the centers of their home galaxies, but it also changes paths of light coming from the stars.

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-   Light from a background source can take different paths around a foreground object as it travels toward Earth, and the closer that path is to an object of great mass, the more it gets "bent." Thus, light from the same object can arrive to Earth at different times as a result of the foreground, or "lensing," object.

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-    This “lensing” can shift the location of the background object in the sky, or it can cause the background object to appear in multiple places in the same image of the sky. Other times, light from the background object is amplified, and thus that object is magnified in the sky.

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-   This effect is known as "gravitational lensing," and the JWST has been using it to great effect to observe ancient galaxies near the dawn of time, which it would otherwise have had no chance of seeing.

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-    To observe the newly studied distant and early dwarf galaxies, and analyze the light they emit, the JWST used a galaxy cluster called “Abell 2744” as a gravitational lens.

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-    Beyond studying the reionization process astronomers will aim to better understand the formation of the very first galaxies, which, over the course of 12 billion years, grew into present-day galaxies.

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-   So far, we've been really studying mostly bright, massive galaxies, but they are not very typical in the early universe.    So if we want to understand the formation of the first galaxies, we really need to understand the formation of tiny, low-mass galaxies. And this is what we will be trying to do with this program.

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February 29, 2024                    FARTHEST  GALAXIES                     4375

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