Are Galaxies Expanding?

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Offline common_sense_seeker

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Are Galaxies Expanding?
« on: 11/09/2008 10:11:16 »
I don't mean by the cosmological expansion or the big bang. Are the stars of a galaxy slowly receding from the galactic centre just like the Moon is receding from the Earth?? It's all the same laws of physics after all. Is this effect measurable?

AL

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Offline Soul Surfer

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Are Galaxies Expanding?
« Reply #1 on: 23/09/2008 15:15:52 »
I do not believe that it is or will ever be possible to actually measure whether the orbits of stars in galaxies are expanding or not.  however they are amenable to dynamical modelling which is how it was initially known that the moon was moving further away from the earth.

Because the stars are all interacting with eash other in a complex way.  The net effect will be that most of the stars will be very slowly moving inwards towards the centre while a few leave the system altogether at high velocities. although indivudual stars may move outwards and inwards in a semi random way while this happens.
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lyner

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Are Galaxies Expanding?
« Reply #2 on: 23/09/2008 18:05:13 »
I don't know how the relativistic effects associated with the SMBH at the centre could alter things but the total angular momentum would need to stay the same. So,  for every star which 'fell' towards the centre and sped up, there would be something else moving away to compensate.

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Offline LeeE

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« Reply #3 on: 24/09/2008 00:01:50 »
I'm pretty sure that individual stars have been tracked and their orbits calculated in some of the closer galaxies to us, with no indication of a general trend for the orbits to decay or enlarge.

In any case, if star orbits within galaxies were to decay or enlarge it would limit the possible lifetime of galaxies as they would eventually either collapse or disperse and there doesn't seem to be any evidence of this - we see no collapsed or dispersed galaxies.

The orbits of stars in galaxies are controlled by gravity whereas the expansion of the universe is not a gravitational phenomenon.
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Offline common_sense_seeker

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« Reply #4 on: 24/09/2008 12:44:53 »
The shape and spiral arm structure of galaxies has been shown by modelling to vary over time, quite dramatically. Is it possible that dark matter (DM) is located at the center of stars, as well as the center of the galaxy? Could galaxies be modelled using this scenario?

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lyner

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« Reply #5 on: 24/09/2008 15:06:31 »
Go on - have a go.

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Offline common_sense_seeker

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« Reply #6 on: 25/09/2008 10:04:16 »
sophie, galaxy computer modellers in another forum site (Sciforums.com) are interested in my ideas. It's out of your knowledge area, you'll admit that surely?

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Offline LeeE

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« Reply #7 on: 25/09/2008 13:31:21 »
If other forums are interested in your ideas why are you irritating us with them here?
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Offline common_sense_seeker

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« Reply #8 on: 25/09/2008 14:02:47 »
I've had interest here to.