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B Intergalactic stars

  1. Feb 29, 2016 #1
    Are all stars contained within a galaxy? Or are there some single stars between galaxies?
    If there are intergalactic stars how were they created since I thought galaxies provided the creation mechanism?

    tex
     
  2. jcsd
  3. Feb 29, 2016 #2

    Janus

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    Yes, there are quite a number of intergalactic, or "rogue" stars. They are generally considered to be stars that originated in galaxies and later ejected by some mechanism like a collision between galaxies or being one of a binary pair that got too close to a super-massive black hole.
     
  4. Feb 29, 2016 #3
    There's definitely inter-galactic stars; a small proportion of stars will get flung out of galaxies as their orbits are perturbed by other stars / black hole etc. A bit like gravity assist for rockets trying to get out of the solar system!

    I'm not aware of star-forming mechanisms that occur outside of galaxies though - someone else may know differently?
     
  5. Feb 29, 2016 #4
    There are lots of them. Lots of times stars are formed in binary systems and when they stray too close to another system, their orbits are completely changed and they lose contact with each other. If either star has the proper speed and trajectory, it'll be ejected from the galaxy the same way that a comet would be from the solar system if tugged on the right way by Jupiter. Galaxies have escape velocities too and it's easily within the reaches of natural processes.
     
  6. Feb 29, 2016 #5
    There are also rogue planets and moons that have been ejected into interstellar and even intergalactic space. Interestingly, the Earth could still sustain life near the ocean floor for billions of years to come while floating alone through the middle of intergalactic space.
     
  7. Feb 29, 2016 #6

    Vanadium 50

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    "Lots" depends on your point of view. There are just shy of a trillion stars in the local group. Perhaps 1000 of them have been ejected from galaxies.

    What evidence do you have that there are rogue planets between galaxies?
     
  8. Mar 1, 2016 #7
    Statistical presumably. Gravity don't care if you're a planet a star. There's plenty of evidence for stars being ejected, same should hold for planets.
     
  9. Mar 1, 2016 #8
    What about stars or planets getting ejected from the Laniakea Supercluster? A galaxy supercluster would presumably be more difficult to escape than a single galaxy.
     
  10. Mar 1, 2016 #9
    According to Wikipedia, the ultimate fate of the Earth may be getting ejected out of the galaxy rather than being swallowed up by the Sun.

    The Milky Way and Andromeda galaxies each contain a central supermassive black hole, these being Sagittarius A* (ca. 3.6 x 106 solar masses) and an object within the P2 concentration of Andromeda's nucleus (1-2 x 108 solar masses). These black holes will converge near the center of the newly formed galaxy, transferring orbital energy to stars that will be moved to higher orbits by gravitationally interacting with them, in a process that may take millions of years. When they come within one light year of one another, they will emit gravitational waves that will radiate further orbital energy until they merge completely. Gas taken up by the combined black hole could create a luminous quasar or an active galactic nucleus. As of 2006, simulations indicated that the future Earth might be brought near the center of the combined galaxy, potentially coming near one of the black holes before being ejected entirely out of the galaxy.
     
  11. Mar 1, 2016 #10

    Vanadium 50

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    There is a difference between "the future Earth might...[be] ejected entirely out of the galaxy" (from Wikipedia no less) and "there are...rogue planets...that have been ejected into...intergalactic space", just as there is a difference between "someday we might colonize Mars" and "we have cities on Mars today".

    You made a factual claim. I don't think there's any evidence at all behind it: in short, I think you just made it up. Prove me wrong. Point me to a reliable reference.
     
  12. Mar 1, 2016 #11

    bcrowell

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    I believe the process of ejection is well understood in terms of thermodynamics. In the very far future, all galaxies are expected to evaporate; this is a generic behavior of any process of evaporation into an infinite space. (The space between galaxies is not infinite, but it will grow without bound due to cosmological expansion.) I think there's a discussion of this sort of thing in this review article: http://arxiv.org/abs/astro-ph/9701131 . Although the arguments about the far future are easier to make, I would assume that one can also calculate the process quite accurately up to the present time.
     
  13. Mar 1, 2016 #12
    There is actually lots of evidence to support the statistical probability of intergalactic planets. In the Virgo Cluster alone it has been suggested that between 7% and 10% of the stellar mass of the cluster is in intergalactic stars. Since ≈60% of all main sequence stars have planets, it would seem highly probable that there would exist intergalactic planets orbiting intergalactic main sequence stars.

    Sources:
    Detection of intergalactic red-giant-branch stars in the Virgo cluster - arXiv 9801228v1
    Planetary Nebulae as Tracers of the Intergalactic Stellar Background: a Population Synthesis Theoretical Approach - arXiv 0407236v1


    Furthermore, they have identified ten possible intergalactic planetary nebulae in the Fornax galaxy cluster. Suggesting that planets, as well as stars, form in intergalactic space.

    Source:

    Intergalactic stars in the Fornax Cluster - arXiv 9609076

    If planets can form around intergalactic main sequence stars, and those intergalactic main sequence stars eventually die, then logically there must be rogue intergalactic planets.

    See also: Wanderers Between the Galaxies
     
  14. Mar 1, 2016 #13

    Vanadium 50

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    And had he said "it's likely [or statistically probable, or similar] that there are extragalactic planets", I wouldn't have said a thing. But he specifically stated that they exist, and when asked for a reference, posted...well, we can all see what he posted. Conclusion: he made it up.
     
  15. Mar 1, 2016 #14
    Sounds like you're denying that extragalactic planets exist.
     
  16. Mar 1, 2016 #15

    ohwilleke

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    Direct observation of something is not the only valid method of scientific proof. In the same vein, we've never directly observed a free up or down quark, because due to confinement in QCD, they don't exist in that form. But, that doesn't mean that we haven't scientifically proven that up and down quarks exist.
     
  17. Mar 1, 2016 #16

    Vanadium 50

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    Sounds like you can't back up a claim you made.
     
  18. Mar 1, 2016 #17

    Sei

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    "Solar System History: Theories Mixed"
    In the early solar system we got hundreds of planetsimals the size of The Moon (Luna) or Mars. They soon interact with each other, fling each other away, collide, gaining speed or crash so hard that they actually destroy each other. Some of the small rogue planet flung by massive planet might be able to gain enough speed to leave the small galaxy (or even larger one), and we got new galactic traveler planet!

    Anyways, lets look at the speed of The Sun (Sol) around galaxy: 220 km/s And the escape velocity: 550 km/s, it's unlikely that a planet could gain such speed, but maybe some planets further away could.

    Another possibility is like having a planetary system went to near a black hole and slingshoted the entire system, planets flung out of the galaxy.
     
  19. Mar 3, 2016 #18
    The biggest problem with the idea of a planet being thrown into intergalactic space that I'm surprised hasn't been mentioned yet is the Roche limit. Intergalactic objects are usually thrown out of the galaxy by very short burst of very high acceleration, like a close pass by a black hole or huge star. A star can survive that in one piece because it's own gravity holds it together. If a planet were to pass at the same distance, the tidal forces would tear it apart.
     
  20. Mar 3, 2016 #19
    Are you saying that no planet is capable of being ejected from any galaxy?
     
  21. Mar 3, 2016 #20
    First, it is an extremely remote chance any star would achieve the escape velocity from its galaxy. It does happen, but very rarely. Second, planets orbiting a star that has been given a gravity-assist and has reached, or exceeded, the galaxy escape velocity of its parent galaxy would remain gravitationally bound to their star. The gravitational field within several dozen AU of such a star would not change much, and therefore would have very little, or no, effect on any planet orbiting such a star.
     
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