Monday, January 23, 2023

3823 - MILKY WAY FACTS - We are still learning?

 

     -  3823  -  MILKY WAY FACTS  -  We are still learning?        We life on a planet circling the sun.  The Sun is a center of solar system of nine planets.  Our Sun is only one of billions of stars in the Milky Way galaxy.   The Milky Way is a “barred spiral” galaxy around 13,600,000,000 years old with large pivoting arms stretching out across the cosmos.

           


            ---------  3823  -    MILKY WAY FACTS  -  We are still learning?

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            ----------------------------   Galaxy type: Barred spiral

            ----------------------------  Age: 13.6 billion years

            ----------------------------   Size: 100,000 light-years across

            ----------------------------  Number of stars: about 200 billion

            ----------------------------  Rotation time: 250 million years

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            -    Our home galaxy's disk is about 100,000 light-years in diameter and just 1,000 light-years thick.

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             -   Just as Earth orbits the sun, the solar system orbits the center of the Milky Way. Despite hurtling through space at speeds of around 515,000 mph our solar system takes approximately 250 million years to complete a single revolution. The last time our planet was in this position, dinosaurs were just emerging and mammals were yet to evolve.

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            -    If the center of the Milky Way were a city, we would be living in suburbia, about 25,000 to 30,000 light-years from the city center. Life in the outskirts is good; we find ourselves nestled in one of the smaller neighborhoods, the Orion-Cygnus Arm, sandwiched between larger Perseus and Carina-Sagittarius arms. If we were to travel inwards towards the city center, we would find the Scutum-Centaurus and Norma arms.

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            -   On a clear night, void of light pollution, we can catch a glimpse of the bright lights of the galactic city streaking across the night sky. Our window into the universe, this milky white band of stars, dust and gas is where our galaxy gets its name.

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            -    Lying at the very heart of the Milky Way is a supermassive black hole called Sagittarius A*. About 4,000,000 times the mass of the sun, this beast consumes anything that strays too close, gorging on an ample supply of stellar material enabling it to grow into a giant.

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            -    In 2022, we imaged this blackhole at the core of our galaxy for the very first time, through an innovative technique allowing us to view the shadow of the black hole.

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            -    Our galactic home is called the Milky Way after its apparent milky white appearance as it stretches across the night sky. In Greek mythology, this milky band appeared because the goddess Hera sprayed milk across the sky.

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            -    Around the world, the Milky Way is known by different names.  In China it is called "Silver River" and in the Kalahari Desert in South Africa it's called the "Backbone of Night". 

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            -    Modern estimates suggest the Andromeda galaxy, our nearest galaxy neighbor is 2.5 million light-years away.   Astronomers have been trying to figure out what type of galaxy the Milky Way is. Our best estimates these days suggest that it is a barred spiral, meaning that there is a bar structure across the center. Astronomers can estimate the shape of the Milky Way by looking at its population of stars, as well as their movements across the sky.

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            -    We now know that the Milky Way resides within the Local Group of galaxies, made up of over 30 galaxies including Andromeda, Triangulum and Leo I to name but a few.

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            -    The Milky Way is currently hurtling towards Andromeda at 250,000 mph. Though there is no need to worry just yet, this crash of cosmic proportions is not due for another 4 billion years.

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            -     Observations of a three-way galactic collision in 2022 using the Hubble Space Telescope gave some intriguing insights. The largest of the group, as it got into a tight orbit with the other two, snagged some material with its relatively stronger gravity. This created an intriguing streak of gas, dust and other materials flowing into the larger galaxy, visible even from Earth.

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            -    While the arms of the Milky Way will surely be ripped up by this process, individual stars are relatively safe as the spaces between them are quite large. Star collisions will be practically non-existent. Starbirth, however, will accelerate due to the amount of gas being pumped into our galaxy, causing our galaxy to brighten and for its population to expand in the coming millions of years following the collision.

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            -    Our own solar system should be relatively safe due to the low risk of star collision.   One practical effect is that the constellations we observe from Earth may change as star orbits alter or new stars are added into the mix; the collision is happening so far in the future that the constellations we see today may be altered in any case, due to natural starbirth and star death outside of the collision.

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            -    Major strides have been made, especially since the 2013 launch of the European Space Agency's (ESA) Gaia mission in reconstructing the shape and structure of our own galactic home. The process involved building catalogs of stars, charting their positions in the sky and determining how far from Earth they are. Gradually, a complex picture emerged of a spiral galaxy that appears quite ordinary.

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            -    At the center of the Milky Way sits a supermassive black hole called Sagittarius A*. With a mass equal to that of four million suns, the black hole, discovered in 1974, can be observed in the sky with radio telescopes close to the constellation Sagittarius.

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            -    Everything else in the galaxy revolves around this powerful gateway to nothingness. In its immediate surroundings is a tightly packed region of dust, gas and stars called the galactic bulge. In the case of the Milky Way, this bulge is peanut-shaped, measuring 10,000 light-years across, according to ESA. It harbors 10 billion stars (out of the Milky Way's total of about 200 billion), mostly old red giants, which formed in the early stages of the galaxy's evolution.

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            -    Beyond the bulge extends the galactic disk. This feature is 100,000 light-years across and 1,000 light-years thick, and it's home to the majority of the galaxy's stars, including our sun. Stars in the disk are dispersed in clouds of stellar dust and gas. When we look up to the sky at night, it's the edge-on view of this disk extending toward the galactic center that takes our breath away.

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            -    Stars in the disk orbit around the galactic center, forming swirling streams that appear to emanate like arms from the galactic bulge.  Inside those arms, stars, dust and gas are more tightly packed than in the more loosely filled areas of the galactic disk, and this increased density triggers more intense star formation. As a result, stars in the galactic disk tend to be much younger than those in the bulge.

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            -    Spiral arms are like traffic jams in that the gas and stars crowd together and move more slowly in the arms. As material passes through the dense spiral arms, it is compressed and this triggers more star formation.

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            -    The Milky Way currently has four spiral arms.  There are two main arms, Perseus and Scutum-Centaurus, and the Sagittarius and Local Arm, which are less pronounced.

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            -   The Milky Way disk is not flat but warped.   As it rotates, it precesses like a wobbling spinning top. This wobble, essentially a giant ripple, circles the galactic center much more slowly than the stars in the disk, completing a full rotation in about 600 to 700 million years. Astronomers think this ripple may be a result of a past collision with another galaxy.

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            -    Sprinkled around the disk and the bulge are globular clusters, collections of ancient stars, as well as approximately 40 dwarf galaxies that are either orbiting or colliding with the larger Milky Way.

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            -    All of that is surrounded by a spherical halo of dust and gas, which is twice as wide as the disk. Astronomers believe that the entire galaxy is embedded in an even larger halo of invisible dark matter.

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            -   Since dark matter doesn't emit any light, its presence can only be inferred indirectly by its gravitational effects on the motions of stars in the galaxy. Calculations suggest that this puzzling stuff makes up to 90% of the galaxy's mass.

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            -   The mass of the Milky Way, dark matter included, equals 1.5 trillion solar masses.  The galaxy's visible matter is distributed between its 200 billion stars, their planets and the massive clouds of dust and gas that fill the interstellar space.

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            -    Astronomers aren't quite sure how many planets are in the Milky Way, given we have only found a few thousand all told, but one NASA estimate suggests it's more than 100 billion planets. How many solar systems there are in the Milky Way is also a mystery, as we are still looking for the planets.

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            -    The sun orbits about 26,000 light-years from the black hole Sagittarius A*, roughly in the middle of the galactic disk. Traveling at the speed of 515,000 mph, the sun takes 230,000,000 years to complete a full orbit around the galactic center.

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            -    The sun sits near the edge of the Local Arm of the Milky Way, one of the two smaller spiral arms of the galaxy. In 2019, using data from the Gaia mission, astronomers found that the sun is essentially surfing a wave of interstellar gas that's 9,000 light-years long, 400 light-years wide and undulates 500 light-years above and below the galactic disk.

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            -   Planets of the solar system do not orbit in the plane of the galaxy but are tipped by about 63 degrees.

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            -    The black hole in the Milky Way, Sagittarius A* is mostly dormant, which makes it very challenging to observe. Sagittarius A* has a mass 4.3 million times that of the sun.   The approximate diameter is 14.6 million miles.   By comparison, the Milky Way itself is roughly 100,000 light-years wide and 1,000 light-years thick.

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            -    A huge disk of gas around Sagittarius A* billows out as far as 5 to 30 light-years from the supermassive black hole. It is this huge area of gas that gives a bit of material for Sagittarius A* activity. The region is known to emit X-rays due to feeding on the gas, or because of friction within the disk as temperatures soar to as much as 18 million degrees Fahrenheit.

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            -     Stellar-mass black holes and intermediate-mass black holes form when huge stars, many times the mass of our sun that collapse after stopping nuclear fusion. Since they are no longer able to stop the gravitational collapse, they shrink to a gravitationally powerful object that can warp time and space around it so much that light no longer can escape.

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            -    The evolution of the Milky Way began when clouds of gas and dust started collapsing, pushed together by gravity. First stars sprung up from the collapsed clouds, those that we see today in the globular clusters. The spherical halo emerged soon after, followed by the flat galactic disk. The galaxy started small and grew as the inescapable force of gravity pulled everything together.

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            -    The Gaia mision measures the exact positions and distances of more than 1 billion stars, as well as their light spectra, which enables scientists to understand the stars' composition and age. The position data allow astronomers to determine the speeds and directions in which the stars move in space.

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            -    As things in space follow predictable trajectories, astronomers can reconstruct the paths of the stars billions of years into the past and future. Combining these reconstructed trajectories into one stellar movie captures the evolution of the galaxy over eons.

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            -    There is evidence that the Milky Way collided with several smaller galaxies during its evolution. In 2018, a team of Dutch astronomers found a group of 30,000 stars moving in sync through the sun's neighborhood in the opposite direction to the rest of the stars in the data set. The motion pattern matched what scientists had previously seen in computer simulations of galactic collisions. These stars also differed in color and brightness, which suggested they came from a different galaxy.

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            -    Remnants of another, slightly younger, collision were spotted a year later. The Milky Way continues devouring smaller galaxies to this day. A galaxy called Sagittarius currently orbits close to the Milky Way and has likely smashed through its disk several times in the past 7 billion years.

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            -   Using Gaia data, scientists found that these collisions triggered periods of intense star formation in the Milky Way and may even have something to do with the galaxy's trademark spiral shape. The study suggests that our sun was born during one of those periods some 4.6 billion years ago.

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            -   Gaia data currently generates more research papers than even the famous Hubble Space Telescope. Gaia will continue charting the galaxy until at least 2025, as long as the spacecraft remains in good health, and the catalog it has compiled will keep astronomers busy for decades to come.

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            -    Even though Gaia sees less than 1% of stars in the galaxy, astronomers can expand their findings and model the behavior of the entire Milky Way.

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            January 22, 2022      MILKY WAY FACTS  -  We are still learning?        3837                                                                                                                             

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            --------------------- ---  Monday, January 23, 2023  ---------------------------

             

             

             

             

                     

             

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