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The star-formation histories and dark-matter content of faint dwarf elliptical galaxies

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Dwarf galaxies hold the key to galaxy evolution

Galaxies come in many shapes and sizes. Among the smallest are dwarf galaxies, on which EU-funded astronomers focused to learn more about the evolution of the Universe and what the future has in store for our own Milky Way.

Climate Change and Environment

In recent years, astronomers have discovered that dwarf galaxies are very different from their bigger relatives. While they spend billions of years in a dormant state, they occasionally experience spectacular periods of star formation. Bursts of star formation also occur in larger galaxies, but light from these bursts is obstructed by other emissions. To get a clear look at this intriguing phenomenon, astronomers working on 'The star-formation histories and dark-matter content of faint dwarf elliptical galaxies' (HOLYDWARFS) project focused on the dwarf family of galaxies. In these smaller versions of 'normal' galaxies, some 30 times smaller than our own Galaxy, they searched for clues of the early history of the Universe. The HOLYDWARFS scientists explored the evolution of galaxies, as star formation is triggered and quenched by environmental effects The main outcome was a unified picture of galaxies in a quiescent state, when all their stars are old, faint and red, with dwarfs that have new, hot and bright blue stars. Thermonuclear reactions transform hydrogen and helium into heavier elements, so-called metals in the area of astronomy and this allows astronomers to follow galaxies' evolution. Project results have provided sufficiently detailed data of the abundance of metals to compare against high-resolution simulations. Comparing observations to simulations offered HOLYDWARFS scientists with a powerful approach to study the physical processed involved in star formation. Hydrodynamical simulations used to form and evolve dwarf galaxies showed that metallicity gradually builds up. Once built up, the metal abundance is maintained in the absence of external disturbances. Besides agreeing with the observed metallicity profiles, the simulations' predictions are hoped to result in better models of dwarf galaxies. According to the widely accepted models, dwarf galaxies that orbit our Milky Way form inside small clumps of dark matter and contain larger proportions of dark matter than their parent galaxy. But what is observed is very different. The HOLYDWARFS project embraced the challenge to uphold existing theories and models and filled some holes in our current understanding of galaxy formation.

Keywords

Dwarf galaxies, Milky Way, star, hydrogen, helium, simulations, metallicity, dark matter

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