Washington | Astronomers have discovered a faint blue galaxy about 30 million light-years from Earth that could shed new light on conditions at the birth of the universe. The galaxy nicknamed Leoncino, or little lion, located in the constellation Leo Minor, contains the lowest level of heavy chemical elements, or metals ever observed in a gravitationally bound system of stars.
Finding the most metal-poor galaxy ever is exciting since it could help contribute to a quantitative test of the Big Bang, said John J Salzer, a professor at Indiana University in the US. There are relatively few ways to explore conditions at the birth of the universe, but low-metal galaxies are among the most promising, Salzer said.
This is because the current accepted model of the start of the universe makes clear predictions about the amount of helium and hydrogen present during the Big Bang, and the ratio of these atoms in metal-poor galaxies provides a direct test of the model. In astronomy, any element other than hydrogen or helium is referred to as a metal. The elemental make-up of metal-poor galaxies is very close to that of the early universe.
Low metal abundance is essentially a sign that very little stellar activity has taken place compared to most galaxies, said lead author Alec S Hirschauer, a graduate student at Indiana University. Leoncino is considered a member of the local universe, a region of space within about 1 billion light years from Earth and estimated to contain several million galaxies, of which only a small portion have been catalogued.
A galaxy previously recognised to possess the lowest metal abundance was identified in 2005; however, Leoncino has an estimated 29 per cent lower metal abundance. The abundance of elements in a galaxy is estimated based upon spectroscopic observations, which capture the light waves emitted by these systems. Regions of space that form stars, for example, emit light that contains specific types of bright lines, each indicating the atoms from various gases: hydrogen, helium, oxygen, nitrogen and more.
In the light of the star-forming region in Leoncino, scientists detected lines from these elements, after which they used the laws of atomic physics to calculate the abundance of specific elements. Aside from low levels of heavier elements, Leoncino is unique in several other ways. A so-called dwarf galaxy, it is only about 1,000 light years in diameter and composed of several million stars.
The Milky Way, by comparison, contains an estimated 200 billion to 400 billion stars. Leoncino is also blue in colour, due to the presence of recently formed hot stars, but surprisingly dim, with the lowest luminosity level ever observed in a system of its type.
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