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Planets in intergalactic space

  1. Feb 8, 2016 #1
    I've seen a number of people write about planets getting ejected from their galaxies as a result of a gravitational sling caused by a black hole. Is this a real thing? I'm having a hard time understanding how gravity in galaxies works. Could a planet in interglactic space be so far out there that it is not affected by any gravitational pull?
     
  2. jcsd
  3. Feb 8, 2016 #2
    Hi Alltimegreat:

    I am not an expert, but I will make a try at answering your question.

    Nothing "is not affected by any gravitational pull". However, some matter, e.g., an isolated planet, may be sufficiently far away from other relatively nearby matter so that it is not gravitationally bound to any other matter.

    One interpretation of this is that the net gravitational force from all other relatively nearby matter cannot accelerate the planet towards the other matter to a greater velocity that the expansion of the universe moves the planet away from the other matter.

    A second interpretation is that the velocity of the planet relative to the center of mass of all the other relatively nearby matter is greater than the escape velocity at the planet's distance from the center of mass of the other matter.

    A third interpretation is that the net gravitational acceleration of the planet towards the center of mass of relatively nearby matter is less than the acceleration of the universe relative to the vector between the planet and the center of mass of the other matter.

    I am curious to see what others might answer.

    Regards,
    Buzz
     
    Last edited: Feb 8, 2016
  4. Feb 8, 2016 #3

    phinds

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    Buzz, I think that's a good set of scenarios.
     
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