- 3490 - MILKY WAY GALAXY - In 1920 the Milky Way was thought to be our entire Universe. Then Edwin Hubble discovered stars in a nebula that turned out to be our neighbor galaxy, the Andromeda. It was 2,500,000 lightyears away and the radius of the Milky Way is only 50,000 lightyears.
--------------------------------- 3490 - MILKY WAY GALAXY
- In 1920 the Milky Way was thought to be our entire Universe. Then Edwin Hubble discovered stars in a nebula that turned out to be our neighbor galaxy, the Andromeda. It was 2,500,000 lightyears away and the radius of the Milky Way is only 50,000 lightyears.
- Andromeda was discovered to be another galaxy outside our galaxy. More galaxies were discovered and most were moving away from us in an expanding Universe. We were not alone.
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- When astronomers saw Andromeda they assumed the Milky Way would have a similar spiral structure in the shape of a rotating disk. “M101” was face-on spiral in the Constellation Ursa Major. It was 25,000,000 lightyears away and 170,000 lightyears across. It held at least a trillion stars.
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- “M51” was also seen face-on a spiral galaxy in Canes Venatici. So, the Milky Way must look similar to these other galaxies.
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- In 1780 astronomers had already deduced the disk shape of our galaxy by simply counting the stars in each direction.
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- In 1927 their measurements were able to prove the galaxy of stars was rotating. The center of rotation was in the Constellation Sagittarius and our Solar System was 26,000 lightyears from the center.
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- In 1951 astronomers gained direct evidence of the galaxy’s spiral arms They thought there were 4 arms caused by spiral compression waves, or density waves, moving around the disk. Stars, gas, and dust would be compressed in the higher density in the arms, increasing the rate of star formation in these areas.
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- In 1930 astronomers concluded that gas and dust in the interstellar medium was absorbing and scattering starlight. This made some stars appear dimmer and redder. The wavelength of visible light is about the same size as the dust particles and the gas molecules. ( about 600 nanometers).
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- Longer wavelengths like infrared and radio pass through dust and gas without scattering. This is similar to small water waves splashing against the side of the boat while the big waves roll right on by.
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- In 1944 astronomers theorized that neutral hydrogen gas would emit light at 21 centimeters wavelength. Once this light was detected the Doppler effect could be used to measure the velocity of the gas moving toward us or away from us. Once the velocity was known the constant rate of expansion of the Universe could calculate the distance for the hydrogen gas. This constant expansion rate was called the “Hubble Constant“. Now the serious mapping of the Milky Way could really make progress.
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- Each hydrogen gas cloud at a different radius was traveling at a different rotational velocity. When the rotational curve was plotted of each measurement spiral arms were evident. The results of this 21 centimeter radio survey was published in 1953.
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- In the 1950’s astronomers began plotting the radio emissions of Carbon Monoxide, CO. With all this data by the 1970’s new mysteries had arisen. At the center of the galaxy was not only rotation faster it was moving away from the core. This suggested a central bar extending 10,000 lightyears on either side of center.
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- Then, at the edges of the disk stars were traveling at too great a velocity to stay in orbit about the center. Like the planets in our Solar System the rotational velocities move slower the farther from the center. The Sun is the center and Mercury is rotating at a much faster velocity than Uranus.
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- Calculations said these stars at the edge of the galaxy should be flung out into outer space. Something 10 times more massive than what we can see is holding them in orbit. It would take a halo of surrounding “Dark Matter” 5 times wider than the visible Milky Way to hold these stars in their orbits.
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- In the 1980’s satellites and balloons were launched above the atmosphere and infrared measurements could be accurately made. The atmosphere blocks infrared radiation from reaching the ground.
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- By 2005 all the measurements combined to give a picture of the Milky Way containing a bar 28,000 light years long angled to us as it rotates around the center. Two spiral arms are attached to the ends of the bar, Scutum-Centaurus and Perseus. There were two minor arms, Sagittarius and Norma.
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- The entire disk is 120,000 lightyears across. Our Solar System is 26,000 lightyears from the center rotating at a velocity or 504,000 miles per hour around the galaxy taking 220,000,000 years to complete one orbit.
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- By 2009 we were way beyond the Milky Way Galaxy in our explorations. What we have learned is that what we see is but a foam on the top of a Cosmic Sea of Darkness. It is like cream on top of the coffee swirling in the cup. The cream is what we can see the coffee is Dark Matter.
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- 83% of all matter is Dark Matter. All matter is only 30% of the matter-energy in the Universe. 70% is Dark Energy. Remember mass-energy are the same, energy equals 90,000,000,000,000,000 times mass. E=mc^2.
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- We see evidence that the Milky Way has cannibalized over 100 Dwarf Galaxies. Looking at these streams of residue matter is teaching astronomers more about the gravity distribution of the Dark Matter surrounding us. Astronomers have pretty much concluded that every galaxy is surrounded by a huge massive halo of Dark Matter, but we still do not know what it is.
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- Dwarf Galaxies are small galaxies of about 1,000 stars that have a total mass of 1,000,000 Solar Mass 300 lightyears across.
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- The Milky Way has a mass of 3,000,000,000,000 Solar Mass and is 120,000 lightyears across.
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- The Blackhole in the center of the Milky Way is 4,300,000 Solar Mass.
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- Great distances in the Universe are measured using Quasars and Supernovae as “standard candles”. If you know how much light they put out and you measure how dim they are you can calculate the distance they are away from you.
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- Also, if the have a “standard light curve” with a known color or frequency you can measure the redshift to determine the distance. Quasars are galaxies with massive Blackholes that are active and spewing jets of energy out their rotational poles.
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- Redshifts of 6 have been measured meaning the during the time the light was traveling the expansion of the Universe has stretched the wavelength, reddened it, to 6 times its original wavelength.
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- An ultraviolet light at 100 nanometer wavelength is received at our telescopes with a wavelength of 600 nanometers. That would mean that the Quasar light left no more than 900,000,000 years after the Big Bang. That would mean the Quasar light was traveling for 12,800,000,000 years duration before we saw it.
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- Supernovae can also have a similar light curve when they explode they become very bright and then dim over a specific time. Astronomers measure these light curve and measure how much they are redshifted.
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- They can use the dimness to measure distance or they can measure the receding velocity and use the Hubble Constant to calculate the distance. The Hubble Constant is the constant expansion of the Universe at 47,000 miles per hour receding velocity per 1,000,000 lightyears. If the velocity is 47 million miles per hour the Supernova is
1 billion lightyears away.
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- Astronomers have very recently determined that going out far enough the expansion of the Universe is actually speeding up. The Supernovae are dimmer than they should be which means the expansion is accelerating. This further adds to the mystery as to what is speeding it up.
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- For lack of a good answer astronomers simply call it “Dark Energy“, a repelling force in the vacuum of space.
- We have come a long way in the past 100 years learning how to map out our Galaxy and beginning to map out the Universe it is in. The more we learn the stranger it gets.
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March 4, 2022 MILKY WAY GALAXY 1058 3490
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