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Thread: More Dumb Questions

  1. #1 More Dumb Questions 
    Time Lord zinjanthropos's Avatar
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    I recently watched a video simulating the collision, or merging, of two galaxies. The video showed many stars being jostled about. I am wondering if such an interaction has the effect of ejecting a star from its galaxy into intergalactic space? If so then does the star stand a good chance of retaining its planetary system? I would imagine such stars exist but has there ever been a calculation made as to how many rogue stars may be traveling within the visible universe? What would the night sky look like from a planet revolving around such a star? Assuming many such merges have taken place since the universe formed, should intergalactic space be riddled with such stars or be practically devoid of them? Can we expect to find stars of every description in intergalactic space?


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  3. #2 Re: More Dumb Questions 
    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by zinjanthropos
    I recently watched a video simulating the collision, or merging, of two galaxies. The video showed many stars being jostled about. I am wondering if such an interaction has the effect of ejecting a star from its galaxy into intergalactic space?
    Disclaimer: I'm not an astrophysicist. I just read books by them in my spare time.

    The answer is, yes. If the merging of the galaxies causes the velocity of some stars in the outer rim of the galaxy to increase velocity, it's quite certainly possible.

    IINM, it's just a simple issue of balance of forces... If the velocity is high enough and the outward/linear/tangential force on the star greater than the gravity holding it to the galaxy then it will fly off. Visualize the concept of gravitational slingshot... how we get our satellites out far into space, as it's similar to that. You pick up speed and sling around the planet if you're not going too fast... but if you are going too fast you escape the gravitational pull and fly off in a straight line outward.



    Quote Originally Posted by zinjanthropos
    If so then does the star stand a good chance of retaining its planetary system?
    Probably not, no. I suppose it's possible, I suspect unlikely. If the velocity is high enough to cause the star to break away from the galaxy's gravity (which is huge), then I find it hard to imagine that the gravity of the star itself would be strong enough to keep the planets surrounding it.


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  4. #3 Re: More Dumb Questions 
    Time Lord zinjanthropos's Avatar
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    I wonder then if stars could be ejected without a galactic merge, like near the center of a galaxy where presumably a black hole exists and stars are moving quickly in close proximity to each other.
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    Veracity Vigilante inow's Avatar
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    The closer to the center you get, the stronger the pull of gravity, so the likelihood of ejection due to velocity goes down accordingly.
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    Comet Dust Collector Moderator
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    Actually, it's the opposite. Close to the center of a galaxy, the odds of either ejection or absorbtion by the central black hole increase.
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    Veracity Vigilante inow's Avatar
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    Okay. I concede that I may have been wrong, but we've both now expressed conflicting views. It would be nice to review with a reference of some sort which is more accurate.
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    Quote Originally Posted by MeteorWayne
    Actually, it's the opposite. Close to the center of a galaxy, the odds of either ejection or absorbtion by the central black hole increase.
    Quote Originally Posted by inow
    Okay. I concede that I may have been wrong, but we've both now expressed conflicting views. It would be nice to review with a reference of some sort which is more accurate.
    Notice MeteorWayne says, "either ejection or absorption". The stronger a gravitational field the longer the associate vector lengths. Bigger results either way.
    Not an exact reference, but I got to go soon; http://en.wikipedia.org/wiki/Gravity_slingshot.
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  9. #8  
    Veracity Vigilante inow's Avatar
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    Of course. Proximity to the gravitational well is not the primary variable. Velocity, and how that velocity interacts with local gravity is. Right on. Thx.


    I should note, I didn't touch many of the questions in the OP, which remain to be addressed.

    Quote Originally Posted by zinjanthropos
    I would imagine such stars exist but has there ever been a calculation made as to how many rogue stars may be traveling within the visible universe? What would the night sky look like from a planet revolving around such a star? Assuming many such merges have taken place since the universe formed, should intergalactic space be riddled with such stars or be practically devoid of them? Can we expect to find stars of every description in intergalactic space?
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  10. #9  
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    Quote Originally Posted by inow
    Of course. Proximity to the gravitational well is not the primary variable. Velocity, and how that velocity interacts with local gravity is. Right on. Thx.

    I should note, I didn't touch many of the questions in the OP, which remain to be addressed.
    Well, your response didn't address the OP questions either. I'm new here so just replied to your post.

    It's actually the kinetic energy of the object in it's orbit and it's interaction with the barycenter of the galaxy that is most important.
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  11. #10  
    Time Lord zinjanthropos's Avatar
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    Quote Originally Posted by MeteorWayne
    It's actually the kinetic energy of the object in it's orbit and it's interaction with the barycenter of the galaxy that is most important.
    Has a stellar ejection ever been witnessed?
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    Veracity Vigilante inow's Avatar
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    Quote Originally Posted by MeteorWayne
    Well, your response didn't address the OP questions either.
    Exactly. That's what I said.


    Quote Originally Posted by MeteorWayne
    It's actually the kinetic energy of the object in it's orbit and it's interaction with the barycenter of the galaxy that is most important.
    Exactly.




    Quote Originally Posted by zinjanthropos
    Quote Originally Posted by MeteorWayne
    It's actually the kinetic energy of the object in it's orbit and it's interaction with the barycenter of the galaxy that is most important.
    Has a stellar ejection ever been witnessed?
    You might look at sites like this:
    http://www.nasa.gov/centers/goddard/...10/10-175.html
    http://hubblesite.org/newscenter/arc.../2010/19/full/


    Others like Dishmaster may know, too.
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  13. #12  
    Time Lord zinjanthropos's Avatar
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    Quote Originally Posted by inow
    Quote Originally Posted by zinjanthropos

    Has a stellar ejection ever been witnessed?
    You might look at sites like this:
    http://www.nasa.gov/centers/goddard/...10/10-175.html
    http://hubblesite.org/newscenter/arc.../2010/19/full/
    Thanks...That was as interesting an article that there can be. Hypervelocity Star is the technical term but I was impressed with the theoretical talk of the Milky Way ejecting one star every 100,000 years. I'm not sure how old our galaxy is but for the Sun's 4.5 billion year history it would mean 45,000 ejections over that time if I did my math right. How many galaxies are there? Must be a lot of ejected stars in intergalactic space.

    Of all the galactic stellar ejecta during the last 4.5 billion years, could a couple of hypervelocity stars have come close enough to Earth to cause some catastrophic events?
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  14. #13  
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    Quote Originally Posted by inow View Post
    Quote Originally Posted by zinjanthropos
    I recently watched a video simulating the collision, or merging, of two galaxies. The video showed many stars being jostled about. I am wondering if such an interaction has the effect of ejecting a star from its galaxy into intergalactic space?
    Disclaimer: I'm not an astrophysicist. I just read books by them in my spare time.

    The answer is, yes. If the merging of the galaxies causes the velocity of some stars in the outer rim of the galaxy to increase velocity, it's quite certainly possible.

    IINM, it's just a simple issue of balance of forces... If the velocity is high enough and the outward/linear/tangential force on the star greater than the gravity holding it to the galaxy then it will fly off. Visualize the concept of gravitational slingshot... how we get our satellites out far into space, as it's similar to that. You pick up speed and sling around the planet if you're not going too fast... but if you are going too fast you escape the gravitational pull and fly off in a straight line outward.

    Quote Originally Posted by zinjanthropos
    If so then does the star stand a good chance of retaining its planetary system?
    Probably not, no. I suppose it's possible, I suspect unlikely. If the velocity is high enough to cause the star to break away from the galaxy's gravity (which is huge), then I find it hard to imagine that the gravity of the star itself would be strong enough to keep the planets surrounding it.
    Two little errors:
    1. "fly off in a straight line outward" / This comment is incorrect. Escape velocities such as those you are discussing are hyperbolas. These are curving away forever. They never return because their speed is too high. It is probable that a straight line is impossible on the galactic scale.
    2. "If the velocity is high enough to cause the star to break away from the galaxy's gravity (which is huge), then I find it hard to imagine that the gravity of the star itself would be strong enough to keep the planets surrounding it." / This is incorrect because the balance of forces you refer to affects the planets of a star exactly the same way as their home star. If these forces are accelerating the star, then they are accelerating the planets as well. The gravity of their home star is far greater than the distant gravity well at their location, so the star's gravity will retain the star's planets as the group is accelerated outward, or inward for that matter. It is one of the facts that is counter intuitive. Heavy items do not free fall faster than lighter items, assuming no atmosphere or magnetic interference. All the items, in this case a star and its planets, will be in a free fall which accelerates them together.
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  15. #14  
    Forum Professor pyoko's Avatar
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    Quote Originally Posted by zinjanthropos View Post
    If so then does the star stand a good chance of retaining its planetary system?
    Actually, yes. The space between stars is relatively huge to the solar system, so it is a fairly safe bet that you can treat each star and contained solar system as one object. It being thrown out of the galaxy would most likely have almost no effect on the planetary system, and it would remain the same (almost).

    P.S. Astronomy is only my hobby and I do not claim to have a degree.
    It is by will alone I set my mind in motion.
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