17 August 2018
UK astronomers, working with colleagues in the USA, have found evidence that the faintest satellite galaxies orbiting our own Milky Way galaxy are amongst the very first that formed in our Universe.
The findings suggest that galaxies including Segue-1, Bootes I, Tucana II and Ursa Major I are in fact some of the first galaxies ever formed and thought to be over 13 billion years old. Our Universe is thought to be 13.8 billion years old.
Professor Carlos Frenk, Director of Durham University’s Institute for Computational Cosmology, said: “Finding some of the very first galaxies that formed in our Universe orbiting in the Milky Way's own backyard is the astronomical equivalent of finding the remains of the first humans that inhabited the Earth. It is hugely exciting.
“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.”
STFC part funded the research of Dr Alis Deason and Professor Carlos Frenk both from Durham University’s ICC who, together with Dr Sownak Bose from Harvard-Smithsonian Center for Astrophysics in the USA, identified two populations of satellite galaxies orbiting the Milky Way.
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.
You can learn more about these findings here.
The imprint of cosmic reionisation on the luminosity function of galaxies, S. Bose et al, The Astrophysical Journal, DOI.