Astronomers have discovered four small galaxies that orbit the Milky Way. These galaxies date back 13 billion years and appeared shortly after the Big Bang, probably the oldest galaxy in the universe.
These dwarf galaxies (also known as satellite galaxies) surround the Milky Way by gravity, just like the relationship between the moon and the Earth, but on a larger scale. The researchers compared the significance of this discovery with “the discovery of the first human remains on Earth.”
Researchers at the Center for Computational Cosmology at Durham University in the United Kingdom and the Harvard-Smithson Center for Astrophysics in the United States say the findings provide new clues for studying the origins of the universe. These satellite galaxies, known as Segue-1, the Dracula Dwarf, the Tucana II, and the Ursa Major I dwarf galaxies, are very faint satellite galaxies and are considered to be the first galaxies formed.
Professor Carlos Frenk, director of the Center for Computational Cosmology at Durham University, said: “In the ‘backyard’ of the Milky Way, some of the earliest galaxies formed in the universe were discovered. This is equivalent to the discovery of the earliest living in astronomy. The human remains on earth. This is really exciting,” said researcher Alice Dyson. “This is a good example to understand the early universe by observing some of the smallest dwarf galaxies in the galaxy.”
It is assumed that when the universe was about 380,000 years old, the first atom was born. These tiny hydrogen atoms are the simplest elements of the periodic table. As the atoms gather together and begin to cool, they gradually stabilize in the dark matter “halo” produced by the big bang. This period of cooling is known as the “era of the universe” and lasted for about 100 million years. Eventually, the gas cooled in the dark matter halo becomes unstable and begins to form stars. These celestial bodies formed the earliest galaxies and brought light to the universe, and the dark age of the universe ended.
The results of this study, published in the recent issue of the Journal of Astrophysics, reveal a group of dwarf galaxies that have formed in the “era of the universe” and are now very bleak. The study also found another group of galaxies that formed slightly brighter after hundreds of millions of years.
Under the intense ultraviolet radiation from the first stars, the hydrogen is ionized and then cooled to form a much larger dark matter halo. It is worth noting that the research team found that a galaxy formation model they had previously developed fits perfectly with the data of these galaxies. This allowed them to infer the timing of the formation of these satellite galaxies. Professor Frenk said: “Our findings support the current model of the evolution of the universe, the ‘ΛCDM model’, in which elementary particles that make up dark matter drive the evolution of the universe.”
The intense ultraviolet radiation from the first galaxies destroys the remaining hydrogen atoms by ionization, making it difficult for the hydrogen cloud to cool and form new stars. In the next few billion years, the formation of galaxies stagnated and no new galaxies could form. Eventually, the dark matter halo becomes so huge that even ionized gases can cool. The galaxies began to reform and eventually emerged in the form of extremely spectacular bright galaxies, such as the Milky Way we are in.
Sonak Boss, a former Ph.D. student at the Center for Computational Cosmology, and now a researcher at the Harvard-Smithsonian Center for Astrophysics, said: “One good aspect of this work is that it emphasizes the theoretical model. The complementarity between the predictions and the real data. Ten years ago, the weakest galaxies near the Milky Way could be ignored by the radar,” Boss added. “With the increasing sensitivity of current and future galaxies, a large number of Small galaxies have emerged that allow us to test theoretical models in new areas.”
Source: spacedaily.com and research paper
Image source: https://www.cfa.harvard.edu/imagelist/2018-17