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Galaxies Distances

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18 years 2 months ago #23488 by ctr
Replied by ctr on topic Re: Galaxies Distances
While also not a cosmologist, is there not Hyperinflation soon after the big bang to take into account.

The furthest galaxies appear very red and therefore are moving the fastest away from us. I read recently that the spectrum of their stars contain very little heavier elements and so are first generation stars. So I suppose they are first generation Galaxies

One question that is needed to be confirmed is if the Milky Way is one of these first generation Galaxies? As we are here I guess not.


If any of the above is complete waffle please understand I'm having a long day. My knowledge on this subject is limited but, like disley, I find it fascinating.

Each of us is here on earth for a reason, and each of us has a special mission to carry out - Maria Shriver

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18 years 2 months ago #23506 by albertw
Replied by albertw on topic Re: Galaxies Distances

Disley, have you come across the balloon analogy of the universe expanding.


I prefer the raisins in a cake analogy :-) You can have light go directly though (you are using transparent flour right?!) basically and raisin will see all the other raisins moving away from it as the cake expands in the oven. Though the universe is thought to be cone chaped and not cake shaped - (dont bother asking me to clarify that! I read it in Nature or somewhere like that in a paper on the WMAP data).

One thing to remember about the deep field images is that most of the prety galaxies are relativly close foreground ones. When astronomers talk about the galaxies that are say 12 billion years away, they are referring to the small smudges of light in the background.

The current speed of expansion is a big matter of debate. Redshift from galaxies outside our local cluster will tell you the current expansion speed over that distance. The change in that speed over time, or the acceleration of the universe is still a hot topic. Though its starting to be settled. They key to measuring acceleration lies with the Hubble Constant. The current value from satelite observations is 71±4 (km/s)/Mpc which is quite a surprise. It was long thought that the universe might constantly expand though decelrate, and perhaps even contract back to a big crunch. 71.4 would mean that the universe is accelerating in its expansion. If you do some reasearch on Hubble's Law you'll get a better understanding of the issues with the expansion of the universe. There are lots of ways of inderectly measuring the hubble constant, one brute force quantity over wuality approach is described in www.irishastronomy.org/user_resources/fi...20454-arc_jan_05.pdf

One school of thought is that the early universe did expand very very quickly. Thats what inflation theory is all about. The theory is needed to explain a couple of issues witht he big bang.

The HDF images were quite a surprise when they appeared. Prior to that there were few galaxies with a redshift of more than 1 known. Galaxies in the deep field go to a redshift of 6, which is where the 12 billion ly figure comes from.

The light horizon of the universe is about 14 billion ly. So from the earth we can see light from things up to 14 billion ly away. The same would go for any raisin in the cake! (forget about the crust). However the universe is much bigger than that, thanks to expansion (and inflation). Currently the universe is at least 40 billion ly wide, or at least 156 billion ly wide. Those numbers depend on dark energy, which I know next to nothing about, other than its thought to be responsible for accelerated expansion. Dark Energy is one of the current trendy topics in cosmology so in the coming years those numbers will be refined.

Seeing galaxies back to 12 billion ly should not be too surprising though. Afterall we have images of the cosmic microwave background which effectivly are images of the universe as it was half a billion years after the big bang.

Cheers

Albert White MSc FRAS
Chairperson, International Dark Sky Association - Irish Section
www.darksky.ie/

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17 years 7 months ago #32782 by Maddad
Replied by Maddad on topic Re: Galaxies Distances
For any of these numbers, 13, 40, or 156 billion light-years, we're talking about the radius of the universe as opposed to its diameter. Makes my head hurt to think about it because I'll never ride my bike that far.

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