A long time ago, in a galaxy far far away…so the story goes

This time the story is about a galaxy of a billion stars that is allegedly seen from a time only 402 million years after the big bang. The galaxy is called GN-z11 because it supposedly has a redshift of 11.1,1 measured with the Hubble Space Telescope (HST). That is the highest redshift assigned to any galaxy to date, and according to big bang cosmology it corresponds to a distance of about 13.4 billion light-years. It allegedly extends the time of observation of the universe back a further 150 million years than previously known. It also places the epoch of this galaxy in the period of predicted formation of a huge number of stars and galaxy formation built from these first stars formed after the alleged big bang.2


Figure 1: That blurry image is of a galaxy so far away it dates closer to the Big Bang, from a time when the universe was a mere toddler of about 400 million years old (so reads the caption from Ref. 6) . Credit: Space Telescope Science Institute via AP.

In a new analysis of the publicly available CANDELS data3 over the GOODS fields,4 a team of astronomers, with lead author Oesch,1 identified six relatively bright galaxies with best-fit photometric redshifts z = 9.2—10.2.  But photometric redshift determinations are very model dependent and not so conclusive, so they chose the intrinsically brightest of them for 12 orbit passes of the HST, to collect grism5 spectroscopic data and more accurately measure its redshift. This galaxy (now called GN-z11) was previously labelled GN-z10-1. It was previously given a photometric redshift zphot = 10.2. It has strong emission in the infrared consistent with a very bright ultra-violet galaxy after taking in to account stretching of the source optical wavelengths down to the infrared. See Fig. 1.

The authors in their paper write:1

GN-z11 is remarkably and unexpectedly luminous for a galaxy at such an early time:

It is about three times brighter than expected for the time of its alleged existence only 400 million years after the big bang. Early in the alleged big bang history, the first stars were supposed to have formed into small nondescript galaxies. They are meant to have many ‘young’ stars but since the galaxies are not meant to be very large it also follows that they should not be very bright. They’re expected to have grown large later by mergers with other galaxies, where galaxy size is correlated with its intrinsic brightness. In this case the GN-z11 galaxy has the intrinsic brightness of a galaxy observed at a redshift near z = 7, at a time when the big bang universe is three times larger. Thus it follows that the only galaxy they have identified at the epoch of 400 million years after the big bang is three times brighter than galaxies when the universe is allegedly much older and when galaxies should be much larger and hence brighter. This means “galaxy evolution” has worked too fast on this newly discovered galaxy. It is the opposite of what is expected.

Is the measurement solid?

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