CfA: Astronomers Identify Some of the Earliest Galaxies in the Universe

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CfA: Astronomers Identify Some of the Earliest Galaxies in the Universe

Post by bystander » Fri Aug 17, 2018 5:27 pm

Astronomers Identify Some of the Earliest Galaxies in the Universe
Harvard-Smithsonian Center for Astrophysics | 2018 Aug 16
Click to view full size image 1 or image 2
The distribution of satellite galaxies orbiting a computer-simulated galaxy, as
predicted by the Lambda-cold-dark-matter cosmological model. Ultrafaint satellites
are amongst the most ancient galaxies in the Universe; they began to form when the
Universe was only about 100 million years old (compared to its current age of 13.8
billion years). The image has been generated from simulations from the Auriga
project. (Credit: Durham ICC/HITS/MPIA/Auriga/S. Bose et al)

Astronomers from Durham University and the Harvard-Smithsonian Center for Astrophysics (CfA) have found evidence that the faintest satellite galaxies orbiting our own Milky Way galaxy are among the very first galaxies that formed in our Universe.

The research group’s results suggest that galaxies including Segue-1, Bootes I, Tucana II and Ursa Major I are, in fact, some of the first galaxies ever formed, thought to be over 13 billion years old. Their findings are published in The Astrophysical Journal.

When the Universe was about 380,000 years old, the very first atoms formed. These were hydrogen atoms, the simplest element in the periodic table. These atoms collected into clouds and began to cool gradually and settle into the small clumps or "halos" of dark matter that emerged from the Big Bang.

This cooling phase, known as the "cosmic dark ages," lasted about 100 million years. Eventually, the gas that had cooled inside the halos became unstable and began to form stars. These objects are the very first galaxies ever to have formed. With the formation of the first galaxies, the Universe burst into light, bringing the cosmic dark ages to an end.

Dr. Sownak Bose of the CfA, working with Dr. Alis Deason and Professor Carlos Frenk at Durham University's Institute for Computational Cosmology (ICC), identified two populations of satellite galaxies orbiting the Milky Way.

The first was a very faint population consisting of the galaxies that formed at the end of the “cosmic dark ages”. 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 (that is, had their electrons knocked out) — by the intense ultraviolet radiation emitted by the first stars was able to cool into more massive dark matter halos. Eventually, the halos of dark matter became so massive that bright galaxies like our own Milky Way were able to form.

Remarkably, the team found that a model of galaxy formation that they had developed previously agreed perfectly with the data, allowing them to infer the formation times of the faint satellite galaxies. ...

Physicists Reveal Oldest Galaxies
Durham University, UK | 2018 Aug 17

The Imprint of Cosmic Reionization on the Luminosity Function of Galaxies - Sownak Bose, Alis J. Deason, Carlos S. Frenk
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