Astronomers Size Up The Smallest Galaxy In The Universe
June 10, 2013

Smallest Dwarf Galaxy In Known Universe Discovered: Segue 2

Lee Rannals for - Your Universe Online

University of California, Irvine scientists reported on Monday that they have measured the least massive galaxy in the known universe.

The researchers wrote in The Astrophysical Journal that the tiny dwarf galaxy, Segue 2, only holds a mere 1,000 stars within its realm. Their findings offer clues about how iron, carbon and other elements help form human life.

“Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse,” said UC Irvine cosmologist James Bullock, co-author of the paper. He said that astronomers' inability to find galaxies this small "has been a major puzzle, suggesting that perhaps our theoretical understanding of structure formation in the universe was flawed in a serious way.”

Scientists have been searching for a dwarf galaxy like this for years around the Milky Way. Bullock said finding Segue 2 around the Milky Way galaxy could be a "tip-of-the-iceberg" observation, hinting at the idea that there could be thousands of these low-mass systems orbiting beyond our detectability.

“It´s definitely a galaxy, not a star cluster,” said postdoctoral scholar and lead author Evan Kirby, adding that the stars are being held together by a globule called a dark matter halo.

Segue 2 has a light output that is just 900 times that of the Sun, compared to our Milky Way galaxy that shines 20 billion times brighter.

“The Keck telescopes are the only ones in the world powerful enough to have made this observation,” Kirby said.

The researchers were able to determine the upper weight range of 25 of the major stars in the galaxy and found that it weighs at least 10 times less than previously estimated.

Segue 2 is a far cry from the galaxy reported in January this year when another group of astronomers discovered the largest known spiral galaxy in the entire universe. This galaxy is more than five times the size of the Milky Way and spans 522,000 light-years across.

Scientists wrote in the journal Nature during the same month that nearly 30 dwarf galaxies orbit the Andromeda galaxy, or Messier 31. This research was crucial in understanding this assembly of small galaxies. This finding helps to shed new light on the theory of how galaxies form.