Telescope Reviews: galaxy group JKCS041 @ 10BLY

My 25" can see large elliptical galaxies out to 3 billion light years. My 18" can see large elliptical galaxies out to around 2 billion light years. This indicates a trend that if you have a telescope with twice the diameter, then you can see twice as far- which makes sense if you plug in the numbers for dimming caused by distance (proportional to 1/d^2) and light gathering power (proportional to r^2). This would mean that roughly, for every inch of aperture, you can see big ellipticals another 111 MLY out into space. So, by this analysis, you would need a 10/0.111 = 90" telescope to see large elliptical galaxies out to 10 billion light years.

HOWEVER, the above analysis is NOT a valid far-field approximation in an expanding universe. A couple factors come into play. First, a galaxy 10 billion light years away first emitted its light when it was alot closer to us, and then the expanding space "slowed" the light down so that it took 10 billion years to reach us. So, angularly, a 10 BLY distant galaxy is going to look a lot closer than 10 BLY. More importantly, however, is that galaxies emit a black-body spectrum- more accurately, a sum of 100 billion or so black body spectrums. That means they emit comparetively little electromagnetic radiation above longer wavelength UV. This is especially true for an old, red, elliptical galaxy. So all that visible and long wavelength UV light will be red-shifted down to IR or at least, red, where are eyes are blind and insensitive, respectively.

One final factor: Big elliptical galaxies didn't even EXIST in the early universe. So the whole premise is flawed. However, in balance, I would assume that some very blue, bright galaxies full of young stars did exist; it's possible that they may have rivaled older and bigger galaxies in luminosity- however, I doubt it.

So with all these factors- redshift, extreme faintness, lack of huge, bright galaxies- I HIGHLY doubt anyone will ever see these objects. The only hope that may exist is if you have some INCREDIBLY powerful UV emitting galaxies that are downshifted to visible light, and you're visually observing with, like, the 5 meter Hale telescope. But from the above anaylsis, I can say with good certainty that even if some large galaxy existed that had a respectable peak in the visible spectrum post-redshift, you'd still need something along the lines of a 100" telescope visually see it. I am not sure of the amount of redshifting that occurs at 10 billion LY, I would have to dig out the forumlas for relativistic redshift, and I have better things to do.

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John T.
Austin, TX
25" f/4.2 Dob
18" Obsession #701
4" Stellar Vue Achromat
8X56 Binos

Edited by tatarjj (10/23/09 02:31 PM)