Tuesday, April 10, 2018

Our closest galaxy?



- 2057  -  Our closest galaxy, not the Andromeda Galaxy.  -  The Andromeda Galaxy is our closest large spiral galaxy.  The closest small galaxies are a formation that is actually within the Milky Way itself.  These are dwarf galaxies that we’ve only known about the last ten years.  The closet known galaxy in the Milky Way is the Canis Major Dwarf Galaxy.   
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----------------------------------  2054  --    Our Closest Galaxy
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-  Scientists have known for some time that the Milky Way Galaxy is not alone in the Universe. In addition to our galaxy being part of the Local Group of galaxies.  The Local Group is a collection of 54 galaxies and dwarf galaxies.   Our galaxy is also part of the larger formation known as the Virgo Supercluster of galaxies.
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-  The Andromeda Galaxy is our closest large spiral galaxy.  The closest small galaxies are a formation that is actually within the Milky Way itself.  These are dwarf galaxies that we’ve only known about the last ten years.
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-   The closet known small galaxy in the Milky Way is the Canis Major Dwarf Galaxy.   This stellar formation is about 42,000 light years from the galactic center, and  25,000 light years from us. This puts it closer to us than the center of our own galaxy, which is 30,000 light years away from the Solar System.
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-   The Canis Major Dwarf Galaxy Dwarf Galaxy is believed to contain one billion stars in all.   A high-percentage of which are in the Red Giant Branch phase of their lifetimes. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way.
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-   In addition to the dwarf galaxy itself, a long filament of stars is visible trailing behind it. This complex, ring like structure wraps around the galaxy three times. It was in the course of investigating this ring of stars that the Dwarf Galaxy was first discovered. The current theory is that this galaxy is being accreted ,or swallowed up, by the Milky Way Galaxy.
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-   Other globular clusters that orbit the center of our Milky Way as a satellite, NGC 1851, NGC 1904, NGC 2298 and NGC 2808,  are thought to have been part of this Dwarf Galaxy before its accretion. It also has associated open clusters, which are thought to have formed as a result of the dwarf galaxy’s gravity perturbing material in the galactic disk and stimulating star formation.
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-   Prior to its discovery, astronomers believed that the Sagittarius Dwarf Galaxy was the closest galactic formation to our own. At 70,000 light years from Earth, this galaxy was determined in 1994 to be closer to us than the Large Magellanic Cloud, the irregular dwarf galaxy that is located 180,000 light years from Earth, and which previously held the title of the closest galaxy to the Milky Way.
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-   All of that changed in 2003 when The Canis Major Dwarf Galaxy was discovered.
The discovery came from a survey of 70% of the sky that detecting about 5,700 celestial sources of infrared radiation. Infrared astronomy takes advantage of advances in astronomy that see more of the Universe because infrared light is not blocked by gas and dust to the same extent as visible light.
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-   Using infrared telescopes the astronomers were able to detect a very significant over-density,  giant stars in a part of the sky occupied by the Canis Major constellation.  The cool, “Red Dwarfs” are not very luminous compared to other classes of stars, and cannot even be seen with the naked eye. However, they shine very brightly in the infrared and appeared in great numbers.
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-   The discovery of this galaxy and the analysis of the stars associated with it has provided some support for the current theory that galaxies may grow in size by swallowing their smaller neighbors. The Milky Way became the size it is now by eating up other galaxies.
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-   The Sagittarius Dwarf Elliptical Galaxy  held the position of closest galaxy to our own prior to 2003 at 75,000 light years away. This dwarf galaxy, which consists of four globular clusters that measure some 10,000 light-years in diameter, was discovered in 1994. Prior to that, the Large Magellanic Cloud was thought to be our closest neighbor.
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-   The Andromeda Galaxy (M31) is the closest spiral galaxy but it is 2,540,000  light years away. Andromeda is currently approaching our galaxy at a speed of about 68 miles per second (244,800 miles per hour). In roughly 4 billion years, the Andromeda Galaxy is expected to merge with our own, forming a single, "super-galaxy".
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-   Astronomers also believe that the Canis Major Dwarf Galaxy is in the process of being pulled apart by the gravitational field of the more massive Milky Way Galaxy. The main body of the galaxy is already extremely degraded, a process which will continue as it travels around and through our Galaxy.
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-  In time, the accretion process will likely culminate with the Dwarf Galaxy merging entirely with the Milky Way depositing its 1 billion stars to the 200 t0 400 billion that are already part of our galaxy.  Let me know how it goes.
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 -------------------------   Tuesday, April 10, 2018   --------------------------------




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