Based on that knowledge, the team identified two populations of satellite galaxies circling the Milky Way. Our own Milky Way galaxy is estimated to be over 13.51 billion years old (give or take millions of years) while the Universe itself is thought to be around 13.8 billion years old.
The image below shows the distribution of satellite galaxies orbiting a computer-simulated galaxy, as predicted by the Lambda-cold-dark-matter cosmological model.
The new study suggests that the first population of dimmer Milky Way satellites are among the oldest galaxies in the universe, which, with the light of their stars, brought an end to the cosmic dark ages.
The galaxies, which are called Segue-1, Bootes I, Tucana II and Ursa Major I, are incredibly faint and believed to be among the first that ever formed.
Phys.org continues, "The intense ultraviolet radiation emitted by the first galaxies destroyed the remaining hydrogen atoms by ionizing them (knocking out their electrons), making it hard for this gas to cool and form new stars".
In the 100 million years that followed the creation of the first atoms - a period referred to by astronomers as the "cosmic dark ages" - the hydrogen slowly cooled and settled into vast haloes made up of dark matter. The gas inside the halos became unstable and began to become stars which can be found in the nearby galaxies. One is very faint, composed of nebulae created during the cosmic dark ages.
It also found a second and slightly brighter group that formed hundreds of millions of years later.
Dr. Alis Deason, who is a Royal Society University Research Fellow at the ICC, Durham University, said: "This is a wonderful example of how observations of the tiniest dwarf galaxies residing in our own Milky Way can be used to learn about the early Universe". The scientists were able to use their model to infer the times at which the satellite galaxies coalesced.
The Lambda-cold-dark-matter model expands on the Big bang theory helps explain the expansion of the universe and formation of galaxies.
Eventually, the halos of dark matter became so massive even ionised gas was able to cool. 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.
"A decade ago, the faintest galaxies in the vicinity of the Milky Way would have gone under the radar", according to Sownak Bose, a former Ph.D. student at the ICC, now a research fellow at the Harvard-Smithsonian Center for Astrophysics. "With the increasing sensitivity of present and future galaxy censuses, a whole new trove of the tiniest galaxies has come into the light, allowing us to test theoretical models in new regimes".