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How fast are we talking here?

  1. Mar 20, 2013 #1
    I'm wondering what sorts of velocities exist for large objects in the universe.

    Specifically, I'm wondering whether huge objects exist which are travelling across the cosmos at huge velocities, and what those objects and velocities might be.

    For example, are there stars moving in intergalactic space which are "whizzing past" other random objects that might wander into their paths? How about within the milky Way Galaxy?

    What sort of relative velocities are galaxies moving at with respect to each other? Are there any examples of galaxies traversing space at an extraordinarily high velocity compared to the norm? In general, are galaxies relatively static WRT each other, or are they all moving around in all directions at significant velocities?
  2. jcsd
  3. Mar 20, 2013 #2


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    In general, as a result of the expansion of the universe, distant galaxies are moving very fast compared to us.
  4. Mar 20, 2013 #3


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    Uhh, this depends on whether you count the velocity due to the expansion of the universe or not. If you do, there are galaxies out there that are receding faster than light. But they aren't "moving through space" at that velocity. Otherwise I know there are large objects traveling very fast. For example, our entire solar system travels at about 251 km/s around the galactic center.
  5. Mar 20, 2013 #4
    Thanks for the replies so far. I wasn't really thinking about the expansion of the universe in general or the relatively uniform orbit of stars around the galactic center.

    But instead, I was wondering if individual objects of size (I suppose at least a solar mass or two) were traveling by themselves in directions other than along with their neighbors?

    Are there any galaxies rushing towards each other? Any stars zipping along at a severe angle to the galactic plane? At what sorts of velocities?
  6. Mar 20, 2013 #5
    Galaxy of Andromeda is rushing towards our own galaxy.
  7. Mar 20, 2013 #6


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  8. Mar 20, 2013 #7


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    It's called "peculiar motion" or "peculiar velocity", and if you look up a star or a galaxy on wikipedia or a catalogue of stellar objects, it's usually noted - if measurable.
    It is defined with respect to some rest frame, usually the "local standard of rest", which is the frame of reference of the solar system as it follows its orbit around the galactic centre.

    Most objects, be it stars or galaxies, exhibit peculiar motion. Stars don't follow strictly regular obits, galaxies gravitationally attract each other and then collide etc.

    Our neighbouring Andromeda Galaxy is currently flying at some 300 km/s toward us(relative to the frame of reference at rest with Milky Way), and is only going to accelerate as it gets closer.

    Individual high speed stars can have peculiar velocities in the order of magnitude of 100s km/s, like this one:
    (here's a pop-sci article about the same thing:)
    http://www.astronomy.com/en/News-Observing/News/2004/11/High-speed star flees Tychos blast.aspx

    Here's some more reading:
    Or search http://arxiv.org/ for "high-velocity stars" "runaway stars", "galactic collision" etc.
  9. Mar 20, 2013 #8
    Good stuff! Thanks.
  10. Mar 21, 2013 #9
    Supernova Remnants like Neutron stars and maybe black holes have the most kinet energies. Since Neutron stars are not that massive (2 solar masses is the upper limit) they can have very high velocities.

    If you're looking for huge Velocities Neutron stars can have up to 1000 km/s (whatch out for "guitar Nebula") and many of them effectively surpassing the galaxy escape velocity (300 km/s). Some of the latest observable pulsars are candidates for even higher velocities.

  11. Mar 21, 2013 #10
    That is exactly the sort of stuff I was wondering about! Thanks.

    Are any of those high-velocity neutron stars headed our way?
  12. Mar 21, 2013 #11


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    Not in such a way that they would come close to our solar system. Space is BIG.
  13. Mar 23, 2013 #12


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    Space is big.
    Space is dark.
    It's hard to find
    A place to park.
    Burma Shave.
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