Thursday, February 9, 2023

3867 - QUASARS - blackhole center of galaxies

 

-  3867  -   QUASARS  -  blackhole center of galaxies.    Discovered 60 years ago quasars have a misleading name. While these objects do shine like a star from our eyes on Earth, they are the brightest objects in the universe.  They’re actually the ultra-bright centers of galaxies powered by powerful supermassive black holes.


-----------  3867  -    QUASARS  -  blackhole center of galaxies?

            -    A “quasar” today is an active galactic nucleus, or a galaxy that has a nucleus with high luminosity in parts of the electromagnetic spectrum. Supermassive black holes can be between millions to billions of times the mass of the Sun.   One exists at the center of every large galaxy.

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            -    The first hints of quasars came in 1908, when Edward Arthur Fath noticed increased luminosity in the center of what were then considered nebulae. Vesto Slipher also examined light spectra from different nebulae and determined that they had unusually bright emission lines. However, they noticed that some emission lines were thick, indicating a range of wavelengths.

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            -    Then in 1918, Hebert Curtis was observing the central object in the Virgo cluster, Messier 87, which famously became home to the image of the first black hole, and he saw a jet coming out of the center of the object, but he had no idea what it was. It was the first observation of an active galactic nucleus jet.

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            -     Astronomers didn’t know that nebula and galaxies were not, in fact, one and the same.  Harlow Shapley and Heber Curtis in the 1920s had this big debate about are the spiral nebulae inside our galaxy or they whole separate island universes, island universes? 

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            -    By the 1930s, we understood thanks to the work of Edwin Hubble that a lot of these smaller nebulae were analogous to our entire Milky Way Galaxy, and were much further away.

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            -    In 1943, Carl Seyfert published a list of galaxies with enhanced activity at their centers, bright spots and fat emission lines. In 1944, radio astronomy was starting up, and scientists started to look for radio signals in the sky.

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            -    In the 1950s,  John Bolton, Gordon Stanley, and Owen Slee were trying to chase down these radio sources using the Parkes Radio Telescope in Australia. They found that tiny distant galaxies were associated with some of the brightest radio sources, which didn’t make much sense to them at the time.    These observations were confirmed in 1962.

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            -     In 1963 Martin Schmidt performed follow-up work on the spectra of the galaxies to confirm that the bright radio sources and galaxies were likely one and the same.

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            -    Eventually, it was suggested that these types of phenomena might be associated with supermassive black holes at the center of a galaxy.  There wasn't any consensus. It really took six years to figure out that these, whatever the hell these things are, they probably must involve a very dense massive object in the center of a galaxy.

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            -     We had a lot of different names for a lot of basically similar things in different ways.   Active galactic nucleus is a good term for any of these objects that basically are quasars with accreting material, releasing energy, releasing energy. And the amount of the efficiency can vary the size can vary the mask or vary, but it pretty much scales.

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            -    While small black holes and supermassive black holes share similar behaviors, they have a different formation process.  They're the same physics because the physics of black holes is just the theory of gravity.   But, there are two ways of squishing something that much, and one of them is killing a star and the other is collapsing part of space-time in the early Universe.

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            -    Supermassive black holes are are ultimately thought to be essential components of a galaxy’s creation and evolution.   The supermassive black hole is the nucleus of the galaxy, surrounded by a galaxy of stars, which is then surrounded by a halo of dark matter. Matter is attracted to the center, but often misses the center of the black hole and instead goes into orbit around it, piling up, lumping together, and forming an accretion disk.

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            -    As the matter orbits the black hole, there is friction within the accretion disk, which makes the matter radiate energy and spiral slowly towards its center; the matter very gradually moving towards the edge of the black hole.

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            -    Orbital speeds increase progressively as the matter approaches the black hole, eventually approaching the speed of light. Once that universal speed limit is reached, though, matter is sucked into the supermassive black hole.

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            -    The process generates heat, and friction, so the disc shines. The closer you are to the black hole, the faster you're going, the hotter you get.  What happens in a certain set of supermassive black holes, is that the black hole is a messy eater, some stuff goes down the black hole, but other stuff, if the disc isn't too thick, you can actually sustain a magnetic field or kind of magnetosphere, around the black hole.

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            -     If the back of the black hole is spinning quite fast, the rotational speed of the event horizon in some senses is spinning near the speed of light and the magnetosphere is spinning, and it catches light, maybe 10 percent of the material shoots it out the north and south poles at speeds close to the speed of light.

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            -     Not only are quasars the brightest objects in the universe, but you see relativistic phenomena associated with them. Because of that, it means they are an extreme physics phenomena and strong gravity phenomena that involve general relativity, and special relativity.

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            -      Different terms are used to imply the total luminosity output of an active galactic nuclei, with quasars being the brightest and are more distant.  Their distance and age can be measured by how much their radiation is redshifted. They are often much brighter than the rest of their host galaxy.

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            -     Another type of galactic nuclei are Seyfert galaxies, which are less luminous and tend to be closer. It is generally thought that Seyfert galaxies are younger.  They interact in a way that at a certain point, you feed the quasar enough that it has a big radiation; stuff comes out and a big jet comes out and blows out the gas that would make more stars, and switches star formation off.  “So, there's a feedback mechanism.”

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            February 8, 2023          QUASARS  -  blackhole center of galaxies       3867                                                                                                                      

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--------------------- ---  Thursday, February 9, 2023  ---------------------------

 

 

 

 

         

 

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