Smallest Galaxy in Known Universe Measured: Tiny System Discovered by Astronomers

You normally wouldn't consider a galaxy to be "tiny;" but in this case, it is. Astronomers have now measured the least massive galaxy in the known universe, and have made some surprising discoveries because of it.

The galaxy is known as Segue 2, and has a mere 1,000 or so stars with a smattering of dark matter holding them together. Because of its small size, it's difficult to find out anything about the galaxy, which is why the researchers employed some of the world's most powerful telescopes. Using instruments at the Keck Observatory, researchers examined the galaxy in order to find a little bit more about it.

"Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse," said UC Irvine cosmologist James Bullock in a news release. Although astronomers have searched for this type of dwarf galaxy for years, they haven't been able to find any--until now. This inability to discover these galaxies "has been a major puzzle, suggesting that perhaps our theoretical understanding of structure formation in the universe was flaws in a serious way," said Bullock.

Segue 2 was actually first discovered in 2009 as part of the massive Sloan Digital Sky Survey. With a light output that's only 900 times that of the sun, the galaxy is 20 billion times dimmer than the Milky Way. Yet it's only now that researchers have gotten a closer look at the galaxy.

"The Keck telescopes are the only ones in the world powerful enough to have made this observation," said Evan Kirby, lead author, in a news release.

The researchers were able to determine the upper weight range of 25 of the major stars in the galaxy. More specifically, they found that the galaxy actually weighs about 10 times less than previously estimated. Essentially, they discovered that the galaxy is even tinier than originally thought.

Since Segue 2 acts as a satellite of our home galaxy, is very possible that more of these miniscule galaxies are out there. Thousands of low-mass galaxies could be waiting to be found. These latest findings show a bit more about this galaxy and offer tantalizing evidence of future discoveries.

The findings are published in The Astrophysical Journal.