The Loh Down On Science

Introducing the smallest galaxy ever found!

Steve Zylius/UC Irvine

Evan Kirby pictured against a background image by S. Garrison-Kimmel.

An itsy-bitsy, teeny-weeny, yellow polka-dot . . . galaxy?

This is Sandra Tsing Loh with the Loh Down on Science.

Introducing the tiny galaxy Segue 2, with its thousand yellow-polka-dot-like stars.

With so few stars, Segue 2 is the smallest galaxy ever found.  Most galaxies contain a hundred billion stars, not a thousand.

Discovered in 2009, at first Segue 2 seemed like just a cluster of stars at the fringe of the Milky Way.  But, now, astronomers at the University of California, Irvine, say little Segue 2 is a galaxy in its own right.  Awww!

James Bullock and Evan Kirby analyzed light coming from 25 stars in Segue 2. Starlight contains information about which elements, like hydrogen or helium, a star is made of.  Turns out Segue 2's stars contain heavier elements, like iron and carbon.  In a star cluster, heavier elements tend to be lost to space.  But in a galaxy, gravity from dark matter keeps them in place.

So little Segue 2 is a galaxy!  Think:  less full Milky Way than . . . fun size.

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The Loh Down on Science is produced by LDOS Media Lab, in partnership with the University of California, Irvine, and 89.3 KPCC. And made possible by the generous support of the Gordon and Betty Moore Foundation.


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