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-1585 - Andromeda, Milky Way Galaxies are on a collision course. What is the tug of war between gravity and Dark Energy? When will the collision happen?
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- The Universe is expanding and galaxies are flying away from each other. A better description would be that the space between galaxies is expanding and pushing galaxies apart from each other. However, this is only on the grander scale. On large scales Dark Energy is dominate. It is the mysterious force that is expanding the vacuum of empty space. This expanding force is in a constant tug of war that is against the attractive force of gravity trying to pull the masses of galaxies back together.
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- So, galaxies flying apart is only true if there is enough space between them where gravity becomes the weaker force. The force of gravity is equal to the product of the masses and inversely equal to the square of the distance between them. The size of the mass and the space between them is what determines what is happening, expansion or collapse.
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- When gravity wins galaxies form into clusters and some galaxies collide with each other forming larger galaxies. The Milky Way Galaxy and the Andromeda Galaxy are part of a Group of 25 galaxies, but, these two are on a collision course. The Andromeda Galaxy , M31, is heading directly towards us at 270,000 miles per hour. Of course, we could just as easily say that the Milky Way is heading directly towards Andromeda. That is the closing speed between us, and, it depends on your point of view which direction it is heading.
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- The force of gravity = Gravitational Constant * Mass * mass / separation distance squared.
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-------------------- F = G * M*m / r^2
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- The mass of the Milky Way Galaxy is 5.68^10^11 Solar Mass.
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- A Solar Mass is the mass of our Sun, which is 2*10^30 kilograms.
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- The mass of the Milky Way Galaxy is 1.14*10^42 kilograms.
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- The mass of the Andromeda Galaxy is 20% larger, 7.1^10^11 Solar Mass, or 1.42*10^42 kilograms.
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- The distance between the galaxies is 2,540,000 lightyears.
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- One lightyear is 9.46*10^15 meters, so , the distance to Andromeda is 24.1*10^21 meters.
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- Solving for the force of gravity, F = (6.67*10^-11) * (1.42*10^42) * (1.14*10^42 ) / (24*10^21)^2
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---------------------------------------- F = 1.87*10^29 kilogram * meters / seconds^2
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- Notice that the units of Force are in F= m*a, mass times acceleration. The unit is called “ Newtons”.
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- At a distance of 2.54 million lightyears closing at a constant speed of 270,000 miles per hour, how long before the galaxies collide?
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--------- time = distance / rate = 2.54*10^6 LY * 9.46*10^15 m / LY / 2.7*10^5 mph *0.447 m/sec / mph / 3.16*10^7 seconds / year.
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--------- time = 6.3*10^9 years.
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- The collision occurs in 6.3 billion years if the closing speed is constant.
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- A more sophisticated calculation has the collision beginning in 4 billion years, but, the whole merger will take another 1 billion years. After 7 billion years the collision is somewhat complete and the new larger galaxy is elliptical, no longer two spiral galaxies.
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- We will have to view from some place else because our Solar System will be cooked by our Sun turning into a Red Giant Star in just 1 billion years.
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- It is surprising to learn that the galaxy collisions present little chance for star collisions. The space between stars is so great that a star to star collision will rarely happen.
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- Today the Andromeda Galaxy appears as a faint white fuzzy cloud about the size of a Full Moon. The galaxy has its own Constellation, Andromeda the Princess, in the north east sky next to the Constellation the Great Square of Pegasus.
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- Precise measurements have been made on the direction and closing speed of the two Galaxies over the past 7 years. The actual intersection will begin in 3.75 billion years. At that point the tidal forces between the two massive galaxies will warp their spiral disks. In 3.85 billion years the shockwaves of gravitational collisions will trigger a burst of new star formations. There will be twice as many stars in the night sky.
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- In 4 billion years the galaxies will pass through each other being tidally stretched and warped beyond recognition.
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- In 5 billion years the stars that pass each other will begin making U-turns being pulled back to the center of gravity.
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- In 7 billion years the stars will be orbiting a common center of gravity and a giant elliptical galaxy will form with a 10 million Solar Mass Blackhole at the center. The Sun may have survived all this chaos but by then it would have burned all its nuclear fuel and be orbiting as a White Dwarf Star. It would be about the size of the Earth but have an extreme density of carbon and oxygen so dense that a teaspoon on Earth would weigh as much as a small truck.
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- We made the 2 body math look pretty simple. In reality the war between gravity and Dark Energy gets very, very complicated. To start with we have the Dark Matter that is surrounding the galaxies in a giant halo. We know the Dark Matter is there because measuring the speed of the stars at the edges of the spiral disks shows they are orbiting too fast to keep from flying out into outer space unless these was 5 times as much mass holding them in place.
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- Besides Dark Matter the Cosmic Web structure of galaxies is very complicated. Starting with these two galaxies being part of a Local Group of 25 galaxies, then this group of galaxies is part of a larger cluster of galaxies which is part of a super cluster of galaxies all connected by filaments of strings of galaxies separated by voids, bubbles of empty space. The filament defines a wall around a void. The space in the void is expanding.
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- Our Galaxy is on a filament moving away from the center of a void toward a Super cluster. The Virgo Cluster is 55 million lightyears away. This Cluster is part of a larger Virgo Supercluster all being pulled toward an even larger super cluster called the Norma-Hydra-Centaurus Supercluster. This Supercluster is being pulled toward a 4 times more massive cluster of galaxies called the Shapley Concentration of galaxy clusters. It is 100 million lightyears away.
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- Meanwhile the voids between those clusters are expanding at an acceleration rate of 47,000 miles per hour per 1 million lightyears of space. Is this not complicated? An announcement will be made shortly, stay tuned.
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RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email upon request. Some reviews are at http://jdetrick.blogspot.com Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net. ---- “Jim Detrick” -- www.facebook.com, -- www.twitter.com, -- 707-536-3272 Tuesday, April 2, 2013
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