How old was the universe after the big bang when galaxies started forming?
The oldest ones observed around around 750Myr after big bang (z=5.5)
See http://antwrp.gsfc.nasa.gov/apod/ap011007.html for the picture of the Abell cluster
Well, we've seen galaxies out to about z=7, but yes, somewhere around 750 million years.
It is safe to say none originated before 400 million years after the big bang. No reason to rule out any afterwards.
Is there any problem with the observation of mature, well-formed galaxies at higher redshift than previously expected?
I'm not so sure that this is the case. The exact formation of the early galaxies has always been uncertain, just because the observations haven't been there.
See for instance however:
You should take all science-related news items with a huge grain of salt. They're often wildly distorted, sometimes just flat wrong.
So far as I know, everybody basically expects a hierarchical formation of galaxies, where galaxies in the densest regions formed first, and galaxies in less dense regions formed later. I don't think there's been anything yet produced that challenges this view, though there are many details that remain to be understood.
Well, these are not news, but a scientific article appeared in Nature:
Cimatti, A. et al., Nature 430 (2004) 184-187.
A good rule of thumb when it comes to stuff like this is that simulations not backed by observation are often wrong.
The nature paper is an observational report, contrarily to what you seem to suggest...
That wasn't my point. My point was that I rather doubt that most physicists were actually surprised by the news that the simulations were entirely accurate.
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