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Astronomers Discovered The Smallest Galaxy in the Universe

Segue 2

Astronomers Discovered The Smallest Galaxy in the Universe

Scientists at the University of California at Irvine have discovered a galaxy so small that it barely even qualifies as a galaxy. Deemed “Segue 2,” the dwarf galaxy only contains about 1,000 stars and is the least massive galaxy in the known universe .

This dwarf spheroidal galaxy contains only a thousand stars and is just barely visible from Earth because it’s so faint. A team of researchers in Hawaii at the W. M. Keck Observatory, the largest observable telescope in the world just published a comprehensive study of Segue 2 in the Astrophysical Journal, revealing that this blip of a galaxy is actually even smaller and dimmer than previously thought.

For the uninitiated, 1,000 stars might sound like a lot, but to grasp just how small Segue 2 is, you have to think in galactic terms. To put it in perspective, our own galaxy, the Milky Way, contains anywhere from 100 to 400 billion stars. Segue 2’s light output — the light output of the entire galaxy — is only equal to about 900 times that of our own meager-sized sun.

Originally discovered in 2007, Segue 2 is scientifically important for reasons beyond its tininess. At the center of the cosmic entity is a clump of dark matter around which the galaxy spins—scientists consider Segue 2 a galaxy rather than a mere star cluster because of this dark matter. Over a hundred light years away, Segue 2 lies in the Aries constellation on a remote stretch of space, where astronomers always expected to find old, weak star systems. But that’s just not the case.

“Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse,” said cosmologist James Bullock, co-author of the paper.

The diminutive galaxy’s discovery begs the question of just how many stars it takes to make a galaxy in the first place. One key qualification is to look at whether the star cluster is bound together gravitationally, and it appears that Segue 2 qualifies. According to the researchers, the stars are bound together by a dark matter halo which acts like a galactic glue, tethering the whole cluster as one.

“It’s definitely a galaxy, not a star cluster,” insisted lead author, Evan Kirby.

Discovering a galaxy as small as Segue 2 is like trying to pick the smallest piece of hay out of a haystack. According to Kirby, there’s only one set of telescopes on Earth that could have detected it: those found at the W.M. Keck Observatory at the summit of Hawaii’s Mauna Kea. In fact, Segue 2’s entry in the record books may only stand for as long as these telescopes remain the most powerful. The galaxy’s discovery suggests that there could be other smaller galaxies lurking out in the darkness, barely faded from view.

There’s a chance that the truly unique nature of Segue 2 could help astronomers better understand the origins of the universe. It could even shed light on the formation of basic elements like carbon and iron. All else fails, it’s a pretty special feather for the eggheads at the W. M. Keck Observatory to stick in their hats. Astronomers say that the latest data on Segue 2 couldn’t have come from any other observatory in the world.

Segue 2’s discovery is not just interesting because of its extreme scantiness. The existence of dwarf galaxies like Segue 2 have long been predicted by models of how the universe was formed. Scientists’ inability to find them, however, “has been a major puzzle, suggesting that perhaps our theoretical understanding of structure formation in the universe was flawed in a serious way,” said Bullock.

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