I Zwicky 18 is a galaxy 45 million light years away. It is named after Swiss astronomer Fritz Zwicky, who first photographed it in the 1930s.
I Zwicky 18 is 500 million years old, which makes it practically an infant (by comparison, most galaxies, including our own Milky Way, are approximately 12 billion years old). It may still be creating Population III stars - spectroscopy shows that its stars are composed almost entirely of hydrogen and helium, with heavier elements almost completely absent.
Hubble Uncovers a Baby Galaxy in a Grown-Up Universe (http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/35/text/)
To prove that I Zwicky18 is a new galaxy, Thuan and Izotov needed to show that it was devoid of stars from the first several billion years after the Big Bang, the period when a large fraction of stars in the universe were formed.
I Zwicky18 is prototypical of this early population of small dwarf galaxies.
Further evidence for the youth of I Zwicky18 is the fact that its interstellar gas is "nearly pristine," Thuan said, and composed mostly of hydrogen and helium - the primary two light elements created in the Big Bang - during the first three minutes of the universe's existence.
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