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B It's not sure but Andromeda will likely hit us -- Is this true?

  1. Jul 18, 2017 #1
    Do some scientists think that Andromeda won't collide with our galaxy?
     
  2. jcsd
  3. Jul 18, 2017 #2

    russ_watters

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    Yes, "collide", but not "hit". Since galaxies are almost entirely empty space, there will be few or possibly even no collisions between actual objects during the process.

    [Edit: Sorry if my reply is confusing. I missed that the question got inverted between the title and body]
     
    Last edited: Jul 18, 2017
  4. Jul 18, 2017 #3
    It'll be more like two clouds merging than two cars crashing.
     
  5. Jul 18, 2017 #4
    I don't think that there are any scientists that think that. It's very obvious based on calculations of gravity and redshift. We know which direction Andromeda is moving relative to us, and we know the approximate mass of both galaxies, so not only are they confident that they'll merge, but they also have a pretty good idea of when: 4-5 billion years.
     
  6. Jul 18, 2017 #5

    phinds

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    Your question conflicts with your title, which is why you have gotten two seemingly contradictory answers to your question. That is, your QUESTION asks is it true that the collision won't happen and as newjerseyrunner states, that is not true. Your SUBJECT line asks will the collision happen and the other answers address this question and of course the answer is yes, it will happen

    Please try to be more clear in the future.
     
  7. Jul 18, 2017 #6

    stefan r

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    Suppose two cars have a frontal collision while each is traveling at 100 kph. None of the 8 tires (10 with spares) make contact with any other tires. Window glass remains window glass. There is no battery-glass alloy. The cars are still recognizable as cars and the owners have them towed and scrapped individually. I would still say they "hit each other".

    All of the features that we use to describe galaxies will change. Spiral arms and bars disappear. If the angle is right you could get a disk but that might as well be called a new disk. Milkomeda is more likely to be an elliptical galaxy than a spiral. The core black holes will merge. Many stars will be thrown out of the system into intergalactic space. Molecular clouds will be subjected to large ram pressure stress. Interstellar gas will heat up and ionize.

    Most planets will be orbiting the same stars. The sun heating up will effect life on earth much more than the galaxy merger.

    Some people think earth is flat. So I am confident you can find someone to back a unique model of the cosmos.

    Andromeda has a strong blue shift. That means it is coming this way fast. The uncertainty is how much sideways motion Andromeda has. An object in a elliptical orbit will also have a blue shift for part of the orbit. There are 2 sets of possible "sideways". The Triangulum galaxy is in the mix too. We can be very certain of impact/merger without knowing a detailed model of the galactic cores' spiral.
     
  8. Jul 18, 2017 #7

    russ_watters

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    Yep, I missed the inversion and my complete answer is "yes, they will collide".
     
  9. Jul 18, 2017 #8
    No, we don´t, actually.
    We don´t know the proper motion very well, and we don´t know the mass at all well. Actually, the official estimates of the mass come from "timing argument", which is a circular argument.
     
  10. Jul 18, 2017 #9
    I could imagine of a lot of ugly things happen during the merger. The central black holes will cross matter rich regions and therefore become active again, radiating a lot of unhealthy radiation. Tidal forces and direct collisions will force protostellar clouds to collapse and produce many new stars followed by super novae. Crossing dust clouds could dim the solar radiation. Close encounters of other stars may destabilize the Oort cloud and the Kuiper belt, resulting in lot of comets or even a new heavy bombardment. And being hit by a comet core from another star with a relative velocity of several hundred km/s would also be no fun.
     
  11. Jul 19, 2017 #10

    stefan r

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    Arcturus, (α boo) has between 1.02 and 1.14 solar mass. It has a 26 solar radius and 170 solar luminosity. Here is a video demonstrating what concentrated what you can do with concentrated sunlight. Not sure how concentrated he got it but 10X magnification is probably the ball park. This will boil water and also melt the glass holding it.

    The dust obscuring the sun might help a little bit but it is not nearly enough. A massive cloud of dust would also reflect heat around from all sides so earth water would still boil.
     
  12. Jul 19, 2017 #11

    phinds

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    Not even close. I estimate the screen is roughly 2'x3', so 864 square inches and the beam at the focal point is no more than 2"x2" (probably less) so 4 sq. in. giving a concentration factor of more like 200+
     
  13. Jul 19, 2017 #12

    stefan r

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    "Concentration factor" is not the same as "magnification". 10X magnification is 100X concentrated. 10X is typical for a magnifying glass. In the video most of the middle hot dog is burning. The entire egg fries. Both would suggest 0.1m (4inch) diameter. He has it more concentrated to melt the pennies. The screen came from a 50" Toshiba television.

    We can also use 1.4 kW/m2 to calculate. So 100 solar luminostiy at 1 au would be 140 kW/m2. Not as much fun as the magnify glass IMO.

    140 kW is 188 horsepower. So the sun as red giant should heat the hood of a car faster than the engine.
     
  14. Jul 20, 2017 #13
    Sun is no red giant during the merger.
     
  15. Jul 21, 2017 #14
    But nevertheless, one cannot forget the fact that it may well upset the structure of our solar system by the intense gravitational forces! (UNLESS, our solar system is such a small unit, that all that will happen is that our solar system will be moved in one direction or another universally, and whatever orbit-based problems we'll encounter will only occur in terms of our entire system's trajectory)

    I would also like to add that this and similar phenomena are so, SO far in the future that we'll have plenty of time to prepare. (I mean, even space travel is not that hard if you think about it, just build a rocket big enough, everything else is basic plumbing and engineering)
     
  16. Jul 21, 2017 #15

    phinds

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    Nonsense.
     
  17. Jul 21, 2017 #16
    GASP I've upset the Time-Space continuum by daring to downplay space exploration as not being the greatest obstacle in mankind's history!!!!!! It's ALMOST LIKE travel in space requires some food, some oxygen, and a sealed TANK. It's ALMOST LIKE space travel is one of the safest forms of travel, because there's LITERALLY NOTHING IN IT
     
  18. Jul 21, 2017 #17

    Vanadium 50

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    Anon500, this is not helpful.
     
  19. Jul 21, 2017 #18
    The solar system is such a tiny dot in galactic terms that three would likely be little disruption. A star may whiz by a light year or so away, but the odds are that it'll be small and likely only knock a few comets out. This event will take place over billions of years itself, everything happens in extreme slow motion at cosmological scales and the distance from Pluto to the sun is 4 orders of magnitude smaller than the distance from the sun to the nearest star.

    Also, there is a lot of stuff in space. Protons traveling near the speed of light, dust particles traveling at a fraction of it...
     
  20. Jul 21, 2017 #19

    stefan r

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    A star (or massive body) that is orbiting around the center of the milky way is far more dangerous. It will be moving slowly relative to the sun which gives the gravity more time to disrupt orbits.
     
    Last edited: Jul 21, 2017
  21. Jul 21, 2017 #20

    phinds

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    The 2nd post to which you are responding was nonsense (you will note that he was banned) and I don't find your response to be much better. You really need to give more thought to what you are talking about.
     
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