Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: drewevans on 13/10/2011 02:35:44

Title: If gravity bends light, what shape is our galaxy when seen from afar?
Post by: drewevans on 13/10/2011 02:35:44

 [;D]
This question will perhaps show my naiivity but I’ve been thinking about it for a while. It’s not a very logical question either but I still think about it.

My question in general is regarding the shape of a galaxy.

Given gravity bends light/time, what effect does that have on an entire galaxy when we look at it from millions/billions of light years away?

Can the distortion created by gravity alter the appearance of a galaxy? If bending of light and time could dictate the shape of a galaxy or an object what would it look like? Could a galaxy be less spiraled than how we actually see it?
Would the overall affect from the gravity from each star within that solar system, within that quadrant, within an arm and within the galaxy itself also play a part in this? That seems like a lot of light bending potential…

Additionally, gravity can affect the colour spectrum too. This doesn’t happen in a vaccum (so i've read) but would the pure density of an entire galaxy affect the bending of colour as well? What would this mean?

Now I certainly don't want to overcomplicate my stupidity bu if a galaxy didn’t spin, hopthetically, could it be possible for the central supermassive black hole to give the illusion of spinning; or the combined gravity of the entire galaxy itself produces a spin… How do we actually know the shape of a galaxy even by looking at it through a telescope?

There are so many ‘ifs’ and double negatives in my questions but it’s purely hypothetical. I’m ignoring my own and current understanding why a galaxy spins because that would defeat the purpose of my questions.

I’m not asking for reasons why this is wrong, or existing theories, but purely the possiblitiy. Does it logically make sense or would this have any bearing on the visual component of a galaxy? If it’s a combination of current theory and potentially the distortion of light then what would the true shape of a galaxy be?

Any help much appreciated.
Thanks.
Andrew.
 [???]

Title: Re: If gravity bends light, what shape is our galaxy when seen from afar?
Post by: Johann Mahne on 13/10/2011 05:43:59

Quote

Can the distortion created by gravity alter the appearance of a galaxy?

  It can even create a mirage, and allow an astronomer to see one galaxy directly behind another in his line of sight, which he normally would not have seen.
It's called "gravitational lensing".
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi56.tinypic.com%2F2dw54c9.png&hash=d3b6efc493c8fced99657f4709933d3d)

Title: Re: If gravity bends light, what shape is our galaxy when seen from afar?
Post by: Soul Surfer on 13/10/2011 16:37:22

All the illustrations of light being deflected by stars and galaxies are massively exaggerated to show the effect it is true that a very distant massive galaxy cluster can distort the image of a vastly distant but bright galaxy and turn it into a curved line but the gravitational distortion of images of almost all the universe that we can see is totally negligible. 

There is only one case where I am concerned about the gravitational distortion of images being important and affecting our understanding and that is the fine structure of the cosmic microwave background radiation.  The current radiation probes are measuring the intensity variations over smaller and smaller patches to look at the distribution of matter at the time the radiation was emitted there WILL come a point when the gravitational distortion of all the lumps of material in between will create a sort of blobby obscured glass distortion to the image. This could in itself contain useful information about the general structure and evolution of the visible universe.   I am not sure how much this effect has been taken into account in analysing the statistics so far.

As far as the colours are concerned gravitational red shift does not apply.  It is only significant for very extreme conditions for radiation originating very close to black holes and neutron stars.  Remember black holes are mostly a few miles across and the very biggest are only about as big as the orbit of Saturn and red shift would only be significant quite close to them.  there is some possibility that there could be a second order effect associated with the many tiny deflections and deviations experienced by the light on its long journey towards us that could cause a very slight dispersion at the very highest energies but this has not been proves inconclusively yet and requires the careful observation of the gamma ray spectrum of large gamma ray bursts and matching them carefully to a model of the process that is generating them

Title: Re: If gravity bends light, what shape is our galaxy when seen from afar?
Post by: drewevans on 14/10/2011 17:51:26

Soul Surfer, Thanks very much for your reply. Exactly what I was looking for.
I don't have a science background so when I come across an image (like the exaggerated shift you mention) it just makes me wonder.