Ancient 'Wimpy' Galaxy is a Cosmic Anomaly

An ancient, failed galaxy is offering astronomers clues about the conditions of the universe in the early stages after the Big Bang.

The galaxy, known as Segue 1, lies on the edge of the universe, about 75,000 light years away. It is the faintest galaxy ever detected and, with only about 1,000 stars, it is abnormally small; a typical galaxy will have closer to 1 million stars.

"It's chemically quite primitive," Anna Frebel, an assistant professor of physics at MIT, said in a statement. "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."

Frebel and her collaborators used data from the Magellan telescopes in Chile and the Keck Observatory in Hawaii to study six giant red stars in Segue 1, the galaxy's brightest objects. 

Instruments on the telescopes are capacble of identifying what elements are present in the stars because each element has a unique signature that becomes visible in the telescope data.

Segue 1, it turns out, has a rare chemical composition with a vanishingly small amount of metallic elements present. The galaxy has effectively shut down, the astronomers report.

"It just didn't have enough gas, and couldn't collect enough gas to grow bigger and make stars, and as a consequence of that, make more of the heavy elements," Frebel said. 

All of the elements in Segue 1 that are heavier than helium appear to have derived from a small number of supernova explosions that would have happened very early in the galaxy's formation.

If astronomers find another wimpy galaxy like Segue 1, they may be able to gain a better understanding of how such galaxies fail to grow in size like their more robust cosmic counterparts.

Frebel said that if another Segue 1-like galaxy is never found it would be an indication of how rare it is for a galaxy to fail in its evolution.

Frebel and her colleagues will publish their research on Segue 1 in the Astrophysical Journal.