Thursday, October 21, 2021

3311 - SUPERNOVAE - what we learn from explosions?

  -  3311   -  SUPERNOVAE  -  what we learn from explosions?   When a star bigger than our Sun burns up all its hydrogen fuel, then its helium fuel, then right up the Periodic Table of Elements,  until it reaches iron, then, the star explodes as a supernova.   


---------------------  3311 -  SUPERNOVAE  -  what we learn from explosions?

-  One of these most luminous supernova explosions ever detected came from the detonation of a dead star within the dense shell of matter ejected from that sun's companion star.

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-  Supernovas are explosions that can happen when stars die, either after the stars burn all their fuel or gain a sudden influx of new fuel.  Once all the elements up to the element iron is in the act of fusion the explosions occurs.    These explosions can briefly outshine all of the other suns in these stars' galaxies, making them visible from halfway across the universe.

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- In 2020 scientists discovered a rare class of exploding star known as “superluminous supernovas“. These explosions are up to 100 times brighter than regular supernovas but account for less than 0.1% of all supernovas.

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-  Much remains unknown about what powers superluminous supernovas. They release far more energy than any standard mechanism for powering supernovas can explain. 

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-  One of the first known superluminous supernovas is “SN 2006gy” that occurred in a galaxy 240 million light-years away and was the brightest and most energetic supernova ever recorded when it was first discovered in 2006.

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-  A little more than a year after this supernova was spotted, researchers detected an unusual spectrum of light from the supernova. Now, scientists have deduced that this light came from an envelope of iron around the supernova, revealing clues as to what might have caused the explosion.

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-  The researchers developed computer models of what kind of light would be generated by envelopes of iron with various masses, temperatures, clumping patterns and other properties. They found that the wavelengths and energies of light seen from this supernova likely came from a huge amount of iron, over a third of the sun's mass,  expanding at about 3,355 mph.

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-  Initial analysis suggested that the supernova happened after a giant star ran out of fuel, with the star's core then collapsing under its own weight into an extraordinarily dense nugget in a fraction of a second and rebounding with a giant blast outward. However, such a "core-collapse" supernova likely would not have generated an iron envelope with the kind of mass and expansion rate that the new study calculated.

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-  Instead,  the new findings suggests that this was a Type 1a supernova, which occurs when one star pours enough fuel onto a dead star known as a white dwarf to trigger an extraordinary nuclear explosion.   White dwarfs are the superdense, Earth-size cores of stars that exhausted all their fuel and shed their outer layers without catastrophic explosions.

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-  For a white dwarf in a close binary orbit with a hydrogen-rich companion star, when such a companion star gets old, it swells, trapping the white dwarf in its expanding shell. The resulting friction causes the white dwarf to spiral towards the center, and at the same time, the envelope material is ejected.

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-  Normally in such binary systems, the white dwarf may spend millions or billions of years spiraling toward the center of its companion before exploding as a Type 1a supernova. However, in this case,  the researchers suspected that the white dwarf may have exploded within only about a century since the initiation of the in spiral phase.

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-  This supernova then slammed into the dense shell of material ejected from the white dwarf's companion star, which was still relatively nearby. Striking this envelope would have been like hitting a brick wall, and most of the motion energy of the supernova was transformed into light in this collision.

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-    Here is another supernova for the record books. This mammoth star explosion occurred in a galaxy about 3.6 billion light-years from Earth and is the brightest supernova ever seen.

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-  Astronomers measure supernovae using two scales: the total energy of the explosion, and the amount of that energy that is emitted as observable light, or radiation.  In a typical supernova, the radiation is less than 1% of the total energy.  But in this case the radiation was five times the explosion energy of a normal-sized supernova. It was the most light astronomers had ever seen emitted by a supernova.

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-  It was so odd and so extreme that it may have been  a "pulsational pair-instability" supernova, in which two big stars merge before the whole system goes boom. Such events are hypothesized, but astronomers have never confirmed their existence observationally.

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-  The research team determined that much of the brightness was derived from the interaction between the supernova and a surrounding shell of gas. Before they explode, doomed giant stars experience violent pulsations, which eject such shells into space.

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-  If the supernova gets the timing right, it can catch up to this shell and release a huge amount of energy in the collision.  In addition, the researchers calculated that the supernova system harbored between 50 and 100 times the mass of the sun. And it may indeed have been a system, not just a single star.

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-  The gas detected was mostly hydrogen, but,  such a massive star would usually have lost all of its hydrogen via stellar winds long before it started pulsating. One explanation is that two slightly less massive stars of around, say 60 solar masses, had merged before the explosion. The lower-mass stars hold onto their hydrogen for longer, while their combined mass is high enough to trigger the pair instability.

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-  The $9,700,000,000  James Webb telescope, Hubble's successor, is scheduled to launch next year, 2022. The new space telescope will conduct a wide range of observations, from studying the formation of the universe's first stars and galaxies to hunting for signs of life in the atmospheres of nearby alien planets.

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-  When a star reaches the end of its life, it explodes in a bright burst as a supernova. “White dwarfs” are the dim, fading corpses of stars that have exhausted most of their nuclear fuel and shed their outer layers. Having shrunk to a relatively small size, white dwarfs are considered among the most stable of stars, given they can last for billions or even trillions of years.

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-  However, when a white dwarf passes near a neighboring star it may siphon too much material from its companion, causing it to grow unstable and explode, resulting in a Type 1a supernova. 

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-  Supernova remnant G344.7-0.1, located 19,600 light years from Earth, is the result of a white dwarf stellar explosion that occurred between 3,000 and 6,000 years ago. The stellar debris expands outward after the initial stellar explosion, then encounters resistance from surrounding gas. 

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-  This resistance slows down the debris, creating a reverse shock wave that travels back toward the center of the explosion, heating the surrounding debris in its path, according to the statement. 

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-  The reverse shock heats the debris to millions of degrees, causing it to glow in X-rays.

G344.7-0.1 is fairly old compared to other well-known Type 1a supernova remnants, which have exploded in the last thousand years or so and not yet encountered the same reverse shock wave that heats the debris at the remnant's core. 

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-  The Chandra X-ray data revealed the supernova remnant contains iron near its core, which is surrounded by arc-like structures containing silicon. The data shows that the regions containing iron were more recently heated by the reverse shock wave, supporting Type 1a supernova models that predict heavier elements, like iron, are produced at the center of these stellar explosions.

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-  There is still a lot to learn from exploding stars. 

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-  October 21, 2021       SUPERNOVAE  -  learn from explosions?      3311                                                                                                                                                   

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