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Can Neutron stars move?

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  • 21-12-2012 10:46am
    #1
    bogwalrus
    Registered Users Posts: 1,454 ✭✭✭


    Hi there,

    I want to know if Neutron stars move through space and could Earth ever be visited by one.


    I've been reading about Neutron stars destroying Earth but how could this happen if they are so far away unless then pick up their bags and move.


    Supposedly our closest Neutron star is in Ursa Minor called Calvera and its between 250-1000 light years away. Could this ever be a threat?

    thanks


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    #2
    28064212
    Registered Users Posts: 10,534 ✭✭✭✭28064212


    All objects move relative to some frame of reference. The Earth doesn't move relative to me, but it does move relative to the sun. The sun moves relative to other solar systems. So the question is, do neutron stars move, relative to the Earth? The answer is yes. Can a neutron star move closer to the Earth (whether that's caused by the Earth's movement or the star's movement)? Yes. Will a neutron star ever move close enough to the Earth to be a threat? That's virtually impossible to say

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    #3
    Rubecula
    Registered Users Posts: 8,551 ✭✭✭Rubecula


    Basically, in space everything is moving around. But the distances are so vast and the time taken to get from one place to another that is noticeably different is so long by human terms then there is not a lot to worry about. As far as I know there is nothing that big actually headed our way.

    Yes our sun is moving about too. It is moving about in the galaxy, which is moving about in the universe, which is itself expanding. The Earth has a number of movements associated with it. It's orbit around our sun, it's "wobble" as it turns on it's axis, and it's actual rotation.

    Like I say, everything moves, but as far as a neutron star arriving at the same place in space as the Earth. It is not going to happen in anything we can currently foresee. So please relax they Mayans did not predict that. :D


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    #4
    henbane
    Registered Users Posts: 1,636 ✭✭✭henbane


    Why a neutron star in particular?


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    #5
    seamus
    Registered Users Posts: 68,317 ✭✭✭✭seamus


    All of the stars are moving all the time - towards each other, away from each other, passing in the night.

    In much the same way that asteroid fields are depicted as being a chaotic mess of rocks flying every which way, so too you can imagine galaxies are like that, with entire star systems moving around at all sorts of velocities.

    The thing is that the space between the stars is quite unimaginably vast. Even on the scale of star, which itself is inconceivably enormous, these distances are so large that the stars themselves are nothing but grains of dust to it. The odds of two stars colliding in our part of the galaxy are negligible.

    At moment the closest known pass of another star to ours will occur in about 1.5m years when Gilese 710 will pass by at a distance of roughly one light-year.
    To give a rough idea of what this would be like, imagine our Solar system (not just our sun) is a beach ball floating in the ocean in Florida. The other solar system would be a beach ball floating in the sea off Portugal, "passing by". The actual stars are 0.5mm dots in the centres of those beach balls - grains of sand.


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    #6
    ps200306
    Registered Users Posts: 1,594 ✭✭✭ps200306


    I like that visualisation, Seamus. :)

    Just to note that the separations between stars isn't the same everywhere. In the centres of globular clusters the average separation can be as small as the dimensions of our solar system ... adjacent beach balls jostling each other.

    Fortunately our solar system is in a relative backwater of the galaxy, far away from the more cosmopolitan central bulge or any of the globular clusters.


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    #7
    Rhys Essien
    Registered Users Posts: 3,029 ✭✭✭Rhys Essien


    OP,were you on about a Rogue Planet(free floating) by any chance?

    http://en.wikipedia.org/wiki/Rogue_planet

    There is an estimation that there are two Rogue Planets for every Star in our galaxy,just drifting along aimlessly.:eek:


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    #8
    bogwalrus
    Registered Users Posts: 1,454 ✭✭✭bogwalrus


    Thanks for your replies,

    That Rogue planet link is scary alright.

    I'm actually trying to write a screenplay where i need to come up with another end of world scenario other than Asteroid etc

    Something that with added CGI would look impressive on the big screen Like a Neutron star sucking the world into it.




    I suppose what i'm on about is the fact that most planets have orbits etc.

    Considering A neutron star is so heavy I imagine it is not in an orbit and freely roaming?

    And if it is Freely Roaming and full of beans (energy) then how fast is it roaming around the place?


    I think my question was already answered above anyway but still interesting these Neutron stars


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    #9
    ps200306
    Registered Users Posts: 1,594 ✭✭✭ps200306


    bogwalrus wrote: »
    I suppose what i'm on about is the fact that most planets have orbits etc.

    Considering A neutron star is so heavy I imagine it is not in an orbit and freely roaming?

    And if it is Freely Roaming and full of beans (energy) then how fast is it roaming around the place?


    I think my question was already answered above anyway but still interesting these Neutron stars

    The fact of being in orbit doesn't really have anything to do with the orbiter's mass. A given gravitational field will produce the same acceleration on all masses. The astronauts on Apollo 15 did a great demo with a hammer and a feather where, in the absence of air resistance, the thousand-times-lighter feather falls at the same speed as the hammer:



    Now consider the moon itself. It is a hundred quadrillion times heavier than the International Space Station. But they both orbit the earth in exactly the same way. What's this got to do with the hammer and the feather? Well, an orbit is just an acceleration, but one with a sideways motion so that the falling object continually misses the thing it is orbiting. If the moon and the ISS were both dropped from the same height above the earth they would fall with the same acceleration. The only difference between the ISS and the moon's orbits is that the moon was "dropped" from higher up.

    Same with a neutron star orbiting the centre of the galaxy. It is no less in orbit than our sun and solar system are. In fact, the ratio of the neutron star's mass to our sun's is much less than the ratio of the hammer and feather masses in the Apollo 15 experiment. Even massive black holes orbit the centre of the galaxy. In fact, even entire galaxies orbit each other. They don't go wandering just because of their mass. It's one of the cool things about gravity -- it's genuinely universal.


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    #10
    Rhys Essien
    Registered Users Posts: 3,029 ✭✭✭Rhys Essien


    ps200306 wrote: »
    The fact of being in orbit doesn't really have anything to do with the orbiter's mass. A given gravitational field will produce the same acceleration on all masses. The astronauts on Apollo 15 did a great demo with a hammer and a feather where, in the absence of air resistance, the thousand-times-lighter feather falls at the same speed as the hammer:



    Now consider the moon itself. It is a hundred quadrillion times heavier than the International Space Station. But they both orbit the earth in exactly the same way. What's this got to do with the hammer and the feather? Well, an orbit is just an acceleration, but one with a sideways motion so that the falling object continually misses the thing it is orbiting. If the moon and the ISS were both dropped from the same height above the earth they would fall with the same acceleration. The only difference between the ISS and the moon's orbits is that the moon was "dropped" from higher up.

    Same with a neutron star orbiting the centre of the galaxy. It is no less in orbit than our sun and solar system are. In fact, the ratio of the neutron star's mass to our sun's is much less than the ratio of the hammer and feather masses in the Apollo 15 experiment. Even massive black holes orbit the centre of the galaxy. In fact, even entire galaxies orbit each other. They don't go wandering just because of their mass. It's one of the cool things about gravity -- it's genuinely universal.

    But Galaxies can and do collide with each other.Andromeda will eventually collide with the Milky Way.As we speak there are Galaxies crashing in to one another.

    http://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision


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    #11
    bogwalrus
    Registered Users Posts: 1,454 ✭✭✭bogwalrus


    ps200306 wrote: »
    The fact of being in orbit doesn't really have anything to do with the orbiter's mass. A given gravitational field will produce the same acceleration on all masses. The astronauts on Apollo 15 did a great demo with a hammer and a feather where, in the absence of air resistance, the thousand-times-lighter feather falls at the same speed as the hammer:



    Now consider the moon itself. It is a hundred quadrillion times heavier than the International Space Station. But they both orbit the earth in exactly the same way. What's this got to do with the hammer and the feather? Well, an orbit is just an acceleration, but one with a sideways motion so that the falling object continually misses the thing it is orbiting. If the moon and the ISS were both dropped from the same height above the earth they would fall with the same acceleration. The only difference between the ISS and the moon's orbits is that the moon was "dropped" from higher up.

    Same with a neutron star orbiting the centre of the galaxy. It is no less in orbit than our sun and solar system are. In fact, the ratio of the neutron star's mass to our sun's is much less than the ratio of the hammer and feather masses in the Apollo 15 experiment. Even massive black holes orbit the centre of the galaxy. In fact, even entire galaxies orbit each other. They don't go wandering just because of their mass. It's one of the cool things about gravity -- it's genuinely universal.


    I never knew that. And it totally just clicked which is a great feeling. I really did think the mass of an object was important in relation to gravitational fields.


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    #12
    ps200306
    Registered Users Posts: 1,594 ✭✭✭ps200306


    Rhys Essien wrote: »
    But Galaxies can and do collide with each other.Andromeda will eventually collide with the Milky Way.As we speak there are Galaxies crashing in to one another.

    http://en.wikipedia.org/wiki/Andromeda–Milky_Way_collision

    Orbital motion is complicated in the case of galaxies. Even though both Andromeda and the Milky Way have "satellite galaxies", the concept of an orbit is an idealisation that can only be approximately applied to a non-rigid assemblage like a galaxy, especially nearby ones. Each star has its own proper motion. The concept of a collision is limited too. When Andromeda and the Milky Way "collide", no stars will hit each other. The individual constituent stars will orbit their mutually common centre of mass. Over a (very long) period of time, the angular momentum is redistributed to give a merged galaxy with more regularised orbits. (Something similar happened in the early solar system to regularise the orbits of the planets -- otherwise we would need very special initial conditions to give the nearly circular planetary orbits that we see). This is a nice visualisation:



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    #13
    ps200306
    Registered Users Posts: 1,594 ✭✭✭ps200306


    bogwalrus, I looked at that neutron star collision video you posted and thought "that looks a bit improbable". Those buildings falling into the sky struck me as a bit of poetic license being taken. I know the phenomenon being portrayed is extreme tidal force, sometimes humorously called "spaghettification". Intuition told me it was being overdone ... but I was wrong. When I went and checked the appropriate spaghettification equations, it looks to me like that could happen once the neutron star was within 50,000 kilometres or so of the earth. (What remains improbable is the idea that we would ever have that close an encounter with another body from outside the solar system).


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    #14
    ThatDrGuy
    Registered Users Posts: 325 ✭✭ThatDrGuy


    bogwalrus wrote: »
    I never knew that. And it totally just clicked which is a great feeling. I really did think the mass of an object was important in relation to gravitational fields.

    Just as interesting is the fact that the feather draws the moon closer too.

    F = GMm/R2

    The force between the feather and the moon can be expressed by this equation where G is gravitational constant, M is the mass of the moon and r^2 is the distance between their centers.

    I remember reading a sci fi story once about a kid who made a microscopic black hole that rapidly enlarged sucking all the matter around it into it, growing larger and larger until it ate the earth. (Way before CERN tried it :)


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