Oldest Ever Galaxies Discovered Outside Milky Way

Rodiano Bonacci
Agosto 18, 2018

The discovery sheds fresh light on the evolution of the universe, according to researchers from the Institute for Computational Cosmology at Durham University and the Harvard-Smithsonian Centre for Astrophysics.

The team discovered that data collected on the two populations agreed well with a theoretical model on galaxy formation that they had developed previously. The first set is over 13 billion years old - among the oldest in the universe.

Professor Frenk said: "Our finding supports the current model for the evolution of our universe - the 'Lambda-cold-dark-matter model" - in which the elementary particles that make up the dark matter drive cosmic evolution'.

Galaxy creation stalled for roughly a billion years as the ionized hydrogen atoms cooled back down to the point where they could settle into larger dark matter haloes, and be used up in the creation of further stars and galaxies. This period is sometimes called the Cosmic Dark Ages because there were no stars or other objects producing light or other frequencies in the electromagnetic spectrum. Hydrogen is the simplest of the known elements and continues to be the most prevalent element in the current-day universe. Once gathered inside the haloes, the vast clouds of hydrogen gradually became unstable and collapsed to form the first stars, and subsequently, the first galaxies.

The study, published in The Astrophysical Journal, identified a very faint population of galaxies that formed during the "cosmic dark ages".

The process of galaxy formation ground to a halt and no new galaxies were able to form for the next billion years or so. The second was a slightly brighter population consisting of galaxies that formed hundreds of millions of years later, once the hydrogen that had been ionized by the intense ultraviolet radiation emitted by the first stars was able to cool into more massive dark matter halos.

The intense ultraviolet radiation emitted by the first galaxies destroyed the remaining hydrogen atoms by ionising them - knocking out their electrons - making it hard for this gas to cool and form new stars. Thus, galaxy formation resumed.

The Lambda-cold-dark-matter model expands on the Big bang theory helps explain the expansion of the universe and formation of galaxies. It would have been impossible to analyze the older dwarf galaxies even ten years ago, but improved instruments allowed the team to determine the properties of these tiny galaxies. The image has been generated from simulations from the Auriga project carried out by researchers at the Institute for Computational Cosmology, Durham University, UK, the Heidelberg Institute for Theoretical Studies, Germany, and the Max Planck Institute for Astrophysics, Germany.' Credit: Institute for Computational Cosmology, Durham University, UK/ Heidelberg Institute for Theoretical Studies, Germany / Max Planck Institute for Astrophysics, Germany.

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