Fossil Galaxy May Be One of First Ever Formed

A tiny galaxy circling the Milky Way may be a fossil left over from the early universe, astronomers say. A recent study found that the stars in the galaxy, called Segue 1, contain fewer heavy elements than those of any other galaxy known, implying that the object may have stopped evolving almost 13 billion years ago. If true, Segue 1 could offer a window into the conditions of the early universe and reveal how some of the first galaxies came to be.

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The first ever galaxies were small irregulars, as we know from the Hubble deep field images. Segue 1 fits that description.

In addition to the uses of Segue 1 in the accompanying article – studying the reionisation period of the early universe etc., the fact that all its stars formed at close to the same time gives us a unique snapshot of stellar evolution for low metal stars. Plot all the stars from Segue 1 on a H-R diagram and you have an isochron for metal-poor stars that can be used to tweak stellar-evolution software.