Friday, May 4, 2018

Quasars and Binary Stars



- 2063  -  Quasars shine so brightly that they eclipse the ancient galaxies that contain them.  Quasars are distant objects powered by blackholes a billion times as massive as our Sun. Most of the quasars have been found to be billions of lightyears away. Because it takes light time to travel, studying objects in space functions much like a time machine. More than 80% of all stars are members of multiple star systems containing two or more stars orbiting each other..  
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-----------------------------  2063  -  Quasars and Binary Stars
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-  Quasars shine so brightly that they eclipse the ancient galaxies that contain them.  Quasars are distant objects powered by blackholes a billion times as massive as our Sun.  In the 1930s, Karl Jansky, a physicist with Bell Telephone Laboratories, discovered that the static interference on transatlantic phone lines was coming from the Milky Way. This was the first indication that a blackhole existed at the center of our galaxy. 
-  By the 1950s, astronomers were using radio telescopes to probe the heavens, and pairing their signals with visible examinations of the heavens.  Astronomers discovered huge amounts of water vapor gas and dust forming a torus around the central blackholes of distant galaxies. There were clouds of charged gas above and below the galaxy centers.   Particles were being  accelerated to velocities approaching the speed of light.
-   These bright electromagnetic emissions became known as Quasars.  They are among the brightest and most distant known celestial objects and are crucial to our understanding of  the early universe.  Quasars live only in galaxies with supermassive blackholes that contain billions of times the mass of the Sun.  Although light cannot escape from the blackhole itself, some signals can break free around its edges and at its poles.
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-  While some dust and gas fall into the blackhole, other particles are accelerated away from it at near the speed of light. The particles stream away in jets above and below transported by one of the most powerful particle accelerators in the universe.  Quasars are thought to form in regions of the universe where the large-scale density of matter is much higher than average.
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-  Most quasars have been found billions of light-years away. Because it takes light time to travel, studying objects in space functions much like a time machine.   We see the object as it was when light left  billions of years ago. The farther away scientists look, the farther back in time they can see. Most of the more than 2,000 known quasars existed in the early life of the galaxy. Galaxies like the Milky Way may once have hosted a quasar that has long since become silent.
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In December, 2017, the most distant quasar was found sitting more than 13 billion lightyears from Earth. Scientists observed the quasar as it appeared only 690 million years after the Big Bang.   Quasars this young can reveal information about how galaxies evolved over time.
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-  Quasars emit energies of millions, billions, or even trillions of electron volts. This energy exceeds the total of the light of all the stars within a galaxy. These brightest objects in the universe shine anywhere from 10 to 100,000 times brighter than our Milky Way.
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-  The ancient quasar , 3C 273, would appear as one of the brightest objects in the sky if it were located 30 lightyears from Earth.   It would appear as bright as the Sun, however, it is 2.5 billion lightyears from Earth.  Quasars are part of a class of objects known as Active Galactic Nuclei. Other classes include Seyfert galaxies and Blazars. All three classifications require supermassive blackholes to power quasars.
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-  Seyfert galaxies have the lowest energy quasars putting out only about 100 kiloelectronvolts.   Blazars, are like their quasar cousins, but put out significantly more energy.
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-  Many scientists think that the three types of galactic nuclei are the same objects, but with different perspectives. While the jets of quasars seem to stream at an angle generally in the direction of Earth, Blazars may point their jets directly toward our planet. Although no jets are seen in Seyfert galaxies, scientists think this may be because we view them from the side, so all of the emission is pointed away from us and thus goes undetected.
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-  In addition to active galaxies we have other multiple star systems to study.  More than 80% of all stars are members of multiple star systems containing two or more stars. Exactly how these systems are formed is not well understood. Some are thought to form when a collapsing cloud of gas breaks apart into two or more clouds which then each become stars.  Another thought is that one star captures another as a result of a grazing collision, or by a close encounters with two or more other stars.
-  The most common multiple star systems are those with two stars. These binary stars have played an important role in many areas of astronomy, especially X-ray astronomy.
-  In many binary systems the stars orbit their common center of mass under the influence of their mutual gravitational force, but they evolve independently. These are called "wide" binaries.  The hot upper atmospheres, or coronas, of these stars can produce X-rays.  Wide binaries are important because they provide the best means for measuring the masses of stars by observing the size and period of the orbit and then applying the theory of gravity equations.
-  In some close binaries the stars are so close together that they can transfer matter to each other and change the way the stars look and evolve.  For example, the evolution of a binary system with two massive stars, A and B, in which A is the most massive. Because of its greater mass, A will become a "red giant star" first. As it expands in size, star A will dump a large fraction of its mass onto star B, changing the appearance of both stars.
-  Star A soon uses up its remaining nuclear fuel and explodes as a supernova leaving behind a neutron star or blackhole. Later, then star B becomes a red giant, material flowing onto the neutron star or blackhole producing a strong X-ray source that is called an X-ray binary. The X-ray power of an X-ray binary is millions of times that of the X-rays from normal stellar coronas.
-  The fate of star B varies depending on the details of its orbit and the masses of the two stars:
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-   (1)   It could spiral into star A to form a large blackhole.
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-   (2  Star  B could explode as a supernova and disrupt the binary system.
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-   (3)   The supernova could produce a neutron star or blackhole, leading to  (3a)   binary neutron star or to  (3b)   a neutron star / blackhole binary, or  (3c)   binary blackholes.
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-  If the masses of stars A and B are comparable to that of the Sun, the end products are white dwarfs instead of neutron stars and blackholes. The dumping of matter from star A onto star B can still result in a strong X-ray source such as a nova, or in rare cases when it transfers too much mass to the white dwarf, a supernova.
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-  There is still much more to learn about Quasars and binary stars.  Stay tuned.
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- May 4, 2018
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