Faintest galaxy ever detected reveals new facts about early universe
Researchers have discovered a new galaxy that is about 75,000 light-years away from us and is the faintest galaxy ever detected.
The galaxy Segue 1 is very small, and contains only about 1,000 stars; it also has a rare chemical composition, with vanishingly small amounts of metallic elements present.
Now a team of scientists, including an MIT astronomer, has analyzed that chemical composition and come away with new insights into the evolution of galaxies in the early stages of our universe -- or, in this case, into a striking lack of evolution in Segue 1.
Anna Frebel, an assistant professor of physics at MIT, and the lead author of a new paper detailing the new findings about Segue 1, said it's chemically quite primitive.
She said this indicates the galaxy never made that many stars in the first place. It is really wimpy. This galaxy tried to become a big galaxy, but it failed.
In particular, Segue 1 has stars that are distinctively poor in metal content. All of the elements in Segue 1 that are heavier than helium appear to have derived either from just one supernova explosion, or perhaps a few such explosions, which occurred relatively soon after the galaxy's formation. Then Segue 1 effectively shut down, in evolutionary terms, because it lost its gas due to the explosions, and stopped making new stars.
The astronomers also found telling evidence in the lack of so-called "neutron-capture elements" -- those found in the bottom half of the periodic table, which are created in intermediate-mass stars. But in Segue 1, Frebel notes, "The neutron-capture elements in this galaxy are the lowest levels ever found." This, again, indicates a lack of repeated star formation.
The findings on Segue 1 also indicate that there may be a greater diversity of evolutionary pathways among galaxies in the early universe than had been thought. However, because it is only one example, Frebel is reluctant to make broad assertions.
The study has been published by the journal Astrophysical Journal.
(Posted on 03-05-2014)