"The onset of spiral structure in galaxies appears to occur between redshifts 1.4 and 1.8 when disks have developed a cool stellar component, rotation dominates over turbulent motions in the gas, and massive clumps become less frequent," write the astronomers.
The redshift of a galaxy directly relates to that galaxy's age. As the Universe expands, ancient light traveling through the universe will get stretched. This ‘light-stretching' is known as redshift. The higher the redshift, the further the light has traveled, so the older it is.
Therefore, from the redshift measurements of this small collection of galaxies in the UDF, the researchers have found that a definite spiral galaxy structure begins to form for galaxies at redshift 1.8, which equates to approximately 3.7 billion years after the Big Bang. However, these are only the embryos of spiral galaxies, the "woolly"-type galaxies with very basic structures smeared with nebulous clouds of star formation. It's not until approximately 8 billion years after the Big Bang (redshift 0.6) that more complex, multi-arm spiral structures form.
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"The observations of different spiral types are consistent with the interpretation that clumpy disks form first and then transition to spirals as the accretion rate and gas velocity dispersion decrease, and the growing population of old fast-moving stars begins to dominate the disk mass," they write.
In a nutshell, early galaxies are a turbulent mess of gas, dust and voracious star formation. These tumultuous times are not conducive to the galaxy settling into a more refined spiral structure. But given enough time, older stars begin to dominate the galactic landscape as the once-giant star formation regions shrink. These factors limit the instabilities throughout the galaxy, heralding a long, quiescent spiral galaxy structure not too dissimilar to the Milky Way's shape some 13.75 billion years after the Big Bang.
As pointed out by The Physics arXiv Blog, although this research goes a long way to describe the evolution of galaxies in the earlier phases of the Universe, it would be interesting to see how dark matter factors in. Dark matter is known to pervade the known Universe and has been linked with galaxy growth. Also, how do the supermassive black holes, known to lurk in the centers of the majority of galaxies, factor into the evolution of spiral galaxies?
This study highlights the incredible power of the Hubble Space Telescope and proves that the data it provides continues to transform how we view the Cosmos.
h/t: The Physics arXiv Blog on Medium.com
Pre-print of publication: The Onset of Spiral Structure in the Universe, Elmegreen and Elmegreen, 2013. arXiv:1312.2215 [astro-ph.CO]