Saturday, March 16, 2024

4386 - JAMES WEBB - finds oldest galaxies?

 

-    4386  -   JAMES  WEBB  -  finds oldest galaxies?       James Webb telescope finds that dwarf galaxies reionized the universe.   Astronomers estimate 50,000 sources of this near-infrared light has traveled through various distances to reach the telescope’s detectors, representing the vastness of space .


-------------------   4386  -   JAMES  WEBB  -  finds oldest galaxies?

-    The concentration of mass in a particular galaxy cluster is so great that the fabric of spacetime is warped by gravity, creating a natural, super-magnifying glass called a 'gravitational lens' that astronomers can use to see very distant sources of light beyond the cluster that would otherwise be undetectable, even to Webb.

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-    Using these unprecedented capabilities scientists have obtained the first spectroscopic observations of the faintest galaxies during the first billion years of the universe. These findings help answer a longstanding question for astronomers: What sources caused the reionization of the universe? These new results have effectively demonstrated that small dwarf galaxies are the likely producers of prodigious amounts of energetic radiation.

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-    The Reionization Era was a period of darkness without any stars or galaxies.  It was  filled with a dense fog of hydrogen gas until the first stars ionized the gas around them, and light began to travel through. Astronomers have spent decades trying to identify the sources that emitted radiation powerful enough to gradually clear away this hydrogen fog that blanketed the early universe.

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-    “Gravitational lensing” magnifies and distorts the appearance of distant galaxies, so they look very different from those in the foreground. The galaxy cluster 'lens' is so massive that it warps the fabric of space itself, so much so that light from distant galaxies that passes through the warped space also takes on a warped appearance.

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-   This magnification effect allowed astronomers to study very distant sources of light beyond “Abell 2744”, revealing eight extremely faint galaxies that would otherwise be undetectable, even to Webb.  These faint galaxies are immense producers of ionizing radiation, at levels that are four times larger than what was previously assumed. This means that most of the photons that reionized the universe likely came from these dwarf galaxies.

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-   This discovery unveils the crucial role played by ultra-faint galaxies in the early universe's evolution.   They produce ionizing photons that transform neutral hydrogen into ionized plasma during cosmic reionization. It highlights the importance of understanding low-mass galaxies in shaping the universe's history.

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-   These cosmic powerhouses collectively emit more than enough energy to get the job done. Despite their tiny size, these low-mass galaxies are prolific producers of energetic radiation, and their abundance during this period is so substantial that their collective influence can transform the entire state of the universe.

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-   This is the first time scientists have robustly measured the number density of these faint galaxies, and they have successfully confirmed that they are the most abundant population during the epoch of reionization. This also marks the first time that the ionizing power of these galaxies has been measured, enabling astronomers to determine that they are producing sufficient energetic radiation to ionize the early universe.

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-    In an upcoming Webb observing program, termed GLIMPSE, scientists will obtain the deepest observations ever on the sky. By targeting another galaxy cluster, named Abell S1063, even fainter galaxies during the epoch of reionization will be identified in order to verify whether this population is representative of the large-scale distribution of galaxies.

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-    The GLIMPSE observations will also help astronomers probe the period known as “Cosmic Dawn”, when the universe was only a few million years old, to develop our understanding of the emergence of the first galaxies. 

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-    Oldest 'dead' galaxy ever seen defies current models of the ancient universe.  This galaxy appears to challenge current models of the early universe.  The newly discovered galaxy, named “JADES-GS-z7-01-QU”, stopped forming stars more than 13 billion years ago, when the universe was only 700 million years old.

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-   Data from the JWST Advanced Deep Survey (JADES) shows that this galaxy most likely had a quick burst of star formation that lasted between 30 million to 90 million years, and then stopped suddenly between 10 million and 20 million years before the point in time observed by the JWST.

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-   Dead galaxies, those that no longer form stars, have been observed in the early universe before.  This one is the oldest such galaxy yet recorded at only 700 million years after the Big Bang that formed the universe 13.8 billion years ago. It is also much smaller than other dormant galaxies previously observed in the early universe.

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-   These recent observations are the deepest views into the distant universe made to date by the JWST. The rapid burst of star formation observed in the galaxy may have exhausted the galaxy's reservoir of dust and gas from which new stars are formed.

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-    Everything seems to happen faster and more dramatically in the early universe, and that might include galaxies moving from a star-forming phase to dormant or quenched.  Given astronomers are still unsure why exactly the galaxy's star formation stopped, or if the galaxy ever came back to life, they plan to find a greater number of old galaxies to help piece together galactic evolution in the early universe and create more accurate models of that time period.

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-   Scientists think that by studying a cluster of "baby quasars," they can get a better understanding of supermassive black holes in the early universe.   Quasars are extremely bright objects powered by actively feeding supermassive black holes at the centers of galaxies. The target quasar emitted its light approximately 13 billion years ago, less than a billion years after the Big Bang.

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-    While these mysterious spots had been previously recorded by the Hubble Space Telescope, it wasn't until scientists viewed them using the far more powerful JWST that they could finally distinguish them from normal galaxies.

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-    Analyzing these tiny dots, which are tinged red by clouds of dust obscuring their light,  required JWST's powerful infrared camera. By studying the different wavelengths of light emitted by the dots, the researchers determined that each one appeared to be a "very small gas cloud that moves extremely rapidly and orbits something very massive young quasar.

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-   The dots don't seem out of place in the early universe.  Yhey are "problematic quasars", ultra-monstrous black holes that appear too massive to exist at such early epochs of the universe.

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-   If we consider that quasars originate from the explosions of massive stars, and that we know their maximum growth rate from the general laws of physics, some of them look like they have grown faster than is possible.

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-   The researchers hope further study of these newly discovered "baby quasars" could help reveal how these problematic black holes grow so big, so fast.  Astronomers have used the JWST  and an effect predicted by Albert Einstein over 100 years ago 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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-   They found galaxies which 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, adding that it's likely the realms supplied most of the energy needed for a process called cosmic reionization.

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-  The main surprise is that these small, faint galaxies had so much power, their cumulative radiation could transform the entire universe.   Prior to around 380 million 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 in the cosmos. 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.  Then, 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. Until now, scientists weren't sure where this ionizing radiation came from.

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-    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, large galaxies with masses in excess of 1 billion suns, and smaller galaxies with masses less than this.

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-    Astronomers didn't think small galaxies would be so efficient at producing ionizing radiation. It's four times higher than what they expected, even for normal-sized galaxies.

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-    JWST has spectroscopic capabilities in the infrared 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 "space-time." Our perception of gravity, the theory says, arises as a result of that curvature. The greater the mass of an object, the more "extreme" the curvature of space-time 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  “Abell 2744” as a gravitational lens.  Even for the JWST, these small galaxies are very faint, we needed to add gravitational lensing to amplify the flux of from them.

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-   Astronomers want to understand the formation of the first galaxies,and they 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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March 13, 2024         JAMES  WEBB  -  finds oldest galaxies?          4386

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