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----------------------------- 2227 - How did galaxies form?
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- How many galaxies are there? How much does our Milky Way Galaxy weigh? Science is trying to use the planet formation model in computer simulations to find that simple collisions of material are not enough energy to form planetesimals and galaxies. There must be other processes involved. Let’s explore:
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- Large galaxies devour smaller galaxies. It is a story of cosmic cannibalism. The Universe is littered with disembodied streams of stars, gas, and dust resulting from galaxy collisions.
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- Our Milky Way Galaxy is a cannibal of smaller dwarf galaxies in our neighborhood. One well documented example is the Sagittarius Dwarf Galaxy that is now a barely discernible pile of stars. There have recently been discovered a dozen long streams of stars that have been pulled apart by the Milky Way’s immense gravity.
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- The Canis Major dwarf galaxy is likely the next target to be devoured by our Galaxy. This would add another 1,000,000,000 stars to the Milky Way.
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- The Large and Small Magellanic Clouds are actually dwarf galaxies that are candidates in our Local Group of galaxies that might be next to merge with the Milky Way.
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- The Milky Way Galaxy may one day be itself prey to a larger galaxy. In 4 to 5 billion years the Andromeda Galaxy may begin to merge with the Milky Way. Today it is 2,500,000 lightyears away but it is hurtling towards us at 250,000 miles per hour.
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- Andromeda Galaxy out weighs our Galaxy two to one. You can see this galaxy in the north-east horizon on a clear night. It’s appears as a fuzz ball. Andromeda will absorb the Milky Way like eating a candy bar. A new greater galaxy will emerge, into the “Milkomeda Galaxy”. Dozens of other dwarf galaxies in our Local Group will also merge with Milkomeda. But, this is at least 4 billion years from now. Don’t hold your breath.
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- When it is all over there will be one giant elliptical galaxy formerly known as the “Local Group”.
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- Cannibal galaxies are messy eaters. Not all the material torn from victims is consumed. Some escape into empty space to become orphaned stars and star clusters.
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- It is not just galaxies that collide, planets and planetesimals collide as well. New evidence is coming together on how our Mother Earth suffered multiple collisions.
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- Astrophysics has revised the estimate of the number of galaxies in the “Observable Universe” from 200 billion to 2,000 billion, or 2 trillion.
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- The Observable Universe is measured to be 13.8 billion lightyears in all directions. That distance is the edge as far as we can see. It takes light that long to reach us, so, that edge today is 46 billion light years away. It is expanding during the time the light is traveling to us. But, we can not see it yet. Have to wait.
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- It is space that keeps stretching out and expanding the Universe. The light photons themselves get stretched out passing through this medium so that visible light and ultraviolet light from the past is stretched into infrared and even microwave wavelengths.
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- Given the volume of the “Observable Universe” with a radius of 13.8 billion lightyears , and, the calculated density of the Universe would put the mass of the Universe at 3.4*10^54 kilograms. This mass calculation includes both Ordinary Matter and Dark Matter. Write the number out to see how big it is. 3.4 followed by 54 zeros.
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- Now divide the total mass by the average galaxy mass and you get 200 billion galaxies. How did we more recently get a number 10 times greater?
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- Astronomers used the Hubble Telescope “ Ultra Deep Field” image. This is staring at one spot in the sky with a very long time exposure. Convert the number of galaxies exposed into a 3 - dimensional map. Then astronomers compared that to a 3-D image of galaxies closet to home which could include the smaller and dimmer dwarf galaxies that would not show up in the Deep Field image.
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- So, the result is not that the Universe is not bigger it just contains more galaxies that have fewer stars in them. The total number of stars in the Observable Universe comes out to the same number when astronomers create a smooth distribution curve from the big galaxies to the tiny dwarf galaxies.
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- The galaxies we can see are just the “ tip of the iceberg”. There are another 9 smaller , fainter galaxies that we can not see. Also, at great distances the light from these galaxies is red-shifted beyond the visible spectrum into the infrared spectrum that we can not see. If we could see all the way into the microwave wavelengths the Universe would glow with stars in all directions.
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- Distant galaxies are red-shifted because they are moving away from us. The light wavelengths get stretched out as the light waves travel toward us. The light looses energy with wider wavelengths. The most distant light is now the Cosmic Microwave Background Radiation which is a lot less energy than the Gamma Rays that started the journey.
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- There are 2 trillion galaxies out there you just can’t see then all. Trust your brain not our eyes this time.
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- The Milky Way Galaxy is between (4*10^11) to (5.8 * 10^11) Solar Mass. We weighed it. That means it contains between 400 to 500 billion Sun-size stars, on average. That particular measure uses the radius of our galaxy to be 311*10^18 miles. If you go out to 746 *10^18 miles you get a mass of 900 billion Solar Mass. This larger mass includes stars, planets, moons, gases, and dust, AND Dark Matter.
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- These mass calculations are being made by using the velocities and positions of globular star clusters that orbit our Galaxy. Velocities must be measured in 2 directions, one along our line of sight, the other across the plane of the sky ( proper motion ). The math uses Bayesian Statistics in a model using 572 parameters to reduce the uncertainties of such a complex measurement. I won’t do the math here. But, trust me. How much does our Galaxy weight? Now you know.
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- Stay tuned. There is much more to learn.. An announcement will be made shortly.
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- Note (1): There are 9 more reviews on the Milky Way starting with Review #1889 and a listing of 8 more. All Reviews are available upon request.
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- January 6, 2018 1919
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-------------------------- Monday, January 7, 2019 --------------------------
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