An image of the galaxy AGC 198691 (nicknamed Leoncino, or “little lion”) taken by the Hubble Space Telescope. Credit: Photo by NASA; A. Hirschauer & J. Salzer, Indiana University; J. Cannon, Macalester College; and K. McQuinn, University of Texas
‘Little lion’ ie Leoncino galaxy contains lowest level of heavy elements ever detected in gravitationally bound system of stars. A faint blue galaxy about 30 million light-years from Earth and located in the constellation Leo Minor could shed new light on conditions at the birth of the universe. “Finding the most metal-poor galaxy ever is exciting since it could help contribute to a quantitative test of the Big Bang,” Salzer said. “There are relatively few ways to explore conditions at the birth of the universe, but low-metal galaxies are among the most promising.”
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. 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.
To find these low-metal galaxies, however, astronomers must look far from home. Our own Milky Way galaxy is a poor source of data due to the high level of heavier elements created over time by “stellar processing,” in which stars churn out heavier elements through nucleosynthesis and then distribute these atoms back into the galaxy when they explode as supernovae. “Low metal abundance is essentially a sign that very little stellar activity has taken place compared to most galaxies,” Hirschauer said.
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 cataloged. A galaxy previously recognized to possess the lowest metal abundance was identified in 2005; however, Leoncino has an estimated 29% lower metal abundance. The abundance of elements in a galaxy is estimated based upon spectroscopic observations.
Regions of space that form stars 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, IU scientists detected lines from these elements, after which they used the laws of atomic physics to calculate the abundance of specific elements.
They userd spectrographs on 2 telescopes in Arizona: the Mayall 4-meter telescope at the Kitt Peak National Observatory and the Multiple Mirror Telescope at the summit of Mount Hopkins near Tucson. The galaxy was originally discovered by Cornell University’s Arecibo Legacy Fast ALFA, or ALFALFA, radio survey project.
Officially, the “little lion” is named AGC 198691. Aside from low levels of heavier elements, Leoncino is unique in several other ways. A so-called “dwarf galaxy,” it’s 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 color, 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.
“We’re eager to continue to explore this mysterious galaxy,” said Salzer, who is pursuing observing time on other telescopes, including the Hubble Space Telescope, to delve deeper into this fascinating object. “Low-metal-abundance galaxies are extremely rare, so we want to learn everything we can.”
http://news.indiana.edu/releases/iu/2016/05/low-metal-galaxy.shtml
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