Looking for clues about the early universe is often like the proverbial needle-in-a-haystack, but once in a while astronomers are able to spot objects that can open new doors into the distant past.
This is the case of AGC 198691, a small blue galaxy located 30 million light-years away in the constellation of Leo Minor. The object has the smallest fraction of heavy elements – referred to as metals in astronomy – ever seen in a galaxy, indicating that its material hasn’t changed much since the Big Bang. A paper describing the discovery was published in the Astrophysical Journal.
"Finding the most metal-poor galaxy ever is exciting since it could help contribute to a quantitative test of the Big Bang," Professor John J. Salzer, of Indiana University and senior author of the paper, said in a statement. "There are relatively few ways to explore conditions at the birth of the universe, but low-metal galaxies are among the most promising."
The metals like carbon, oxygen, and so on are produced by stars and spread throughout interstellar space by supernovae. AGC 198691 has just 1.3 percent the metallicity of the Sun, a sign that very little star formation has happened since its formation.
Without much "contamination," the composition of the galaxy, which has been nicknamed Leoncino (Italian for "little lion"), can be used to compare whether the predicted abundance of primordial hydrogen and helium matches with the observations.
Leoncino’s uniqueness doesn’t stop at its low metallicity. The galaxy is a "dwarf," about 1,000 light-years across and made of a few million stars. An average system like the Milky Way is about 100 times wider and contains between 200 and 400 billion stars. Although Leoncino has some recently formed stars, responsible for its blue color, the galaxy has the lowest luminosity ever observed for this kind of object.
"We're eager to continue to explore this mysterious galaxy," added Salzer. "Low-metal-abundance galaxies are extremely rare, so we want to learn everything we can."
The team is pursuing follow-up observations with several instruments, including the Hubble Space Telescope. A better understating of these galaxies will lay the groundwork for the potential detection of even more metal-poor objects by the next generation of observatories.