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Originally Posted by Pluto
Galaxy clusters of galaxies are big, very big and I'd like someone to explain to me how they could be formed in just 700 million years.
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The article you've got there says that galaxies in the 700 million year old universe were small:
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Originally Posted by ESA/Hubble article
The relatively high number of redshift 7.5 galaxies claimed in this survey suggests that most of the ionising energy was produced by dim and abundant galaxies rather than large, scarce ones.
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As Craig explains, you've mixed up the closer galaxy clusters with the very distant, young galaxies. The paper talks about both. To learn more about gravitational lensing, you could read the article you linked which has this to say:
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This new result was only made possible with some cosmic assistance in the form of gravitational lensing that magnified the light from the distant galaxies enough for Hubble to detect them. A firm confirmation of their distance was beyond even the capabilities of the 10-meter Keck telescope and must await powerful future ground-based telescopes.
First observationally confirmed in 1979, gravitational lenses were predicted by Albert Einstein’s theory of General Relativity, a theory that allows astronomers to calculate the path of starlight as it moves through curved space-time. According to the theory, the bending of light is brought about by the presence of matter in the Universe, which causes the fabric of space-time to warp and curve.
Gravitational lensing is the result of this warping of spacetime and is mainly detected around very massive galaxy clusters. Due to the gravitational effect of both the cluster’s observable matter and hidden dark matter, the light is bent around the cluster. This bending of light allows the clusters in certain places to act as natural gravitational telescopes that give the light of faint and faraway objects a boost.
Where Earth-bound telescopes fail to detect such faint and distant objects due to the blurring introduced by the Earth’s atmosphere, a combination of Hubble’s location in space and the magnification of the gravitation lenses provides astronomers with a birds-eye view of these elusive objects.
This technique has already been used numerous times by Hubble and has helped astronomers to find and study many of the most distant known galaxies.
-European Homepage for Hubble
(copyright free)
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~modest
