Beautiful spiral galaxies were ‘ugly ducklings’ 6 bln yrs ago
Paris: The Hubble Space Telescope has shown that the beautiful spirals galaxies of the modern Universe were the ugly ducklings of six billion years ago.
Using data from the NASA/ESA Hubble Space Telescope, astronomers created a census of galaxy types and shapes from a time before Earth and the Sun existed, up to the present day.
The results show that, contrary to contemporary thought, more than half of the present-day spiral galaxies had peculiar shapes as recently as six billion years ago.
Hubble’s scheme divides regular galaxies into three broad classes — ellipticals, lenticulars and spirals — based on their visual appearance.
A fourth class contains galaxies with an irregular appearance.
A team of European astronomers led by Francois Hammer of the Observatoire de Paris has, for the first time, completed a census of galaxy types at two different points in the Universe’s history — in effect, creating two Hubble sequences — that help explain how galaxies form.
In this survey, researchers sampled 116 local galaxies and 148 distant galaxies.
The astronomers show that the Hubble sequence six billion years ago was very different from the one that astronomers see today.
“Six billion years ago, there were many more peculiar galaxies than now – a very surprising result,” said Rodney Delgado-Serrano, lead author of the related paper recently published in Astronomy and Astrophysics.
“This means that in the last six billion years, these peculiar galaxies must have become normal spirals, giving us a more dramatic picture of the recent Universe than we had before,” he added.
The astronomers think that these peculiar galaxies did indeed become spirals through collisions and merging.
Although it was commonly believed that galaxy mergers decreased significantly eight billion years ago, the new result implies that mergers were still occurring frequently after that time — up to as recently as four billion years ago.
“Our aim was to find a scenario that would connect the current picture of the Universe with the morphologies of distant, older galaxies — to find the right fit for this puzzling view of galaxy evolution,” said Hammer.
Also contrary to the widely held opinion that galaxy mergers result in the formation of elliptical galaxies, Hammer and his team support a scenario in which these cosmic clashes result in spiral galaxies.
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