October 16, 2007—For decades a dwarf galaxy called I Zwicky 18 was thought to be one of the youngest galaxies in the universe. But new images showing faint, red stars inside the galaxy reveal that the "toddler" might be a good deal older than it seemed.
When it was first observed by ground-based telescopes in the 1930s, I Zwicky 18 seemed to sit about 45 million light-years away. At a mere 500 million years old, the galaxy was just a baby compared to the multibillion-year-old cosmic grown-ups surrounding it.
The find offered researchers the opportunity to study such a young galaxy up close—a rarity because the youngest galaxies are usually those that are farthest away.
But astronomers using the NASA/ESA Hubble Space Telescope captured detailed new snapshots—including the image above—of the seemingly young galaxy in 2005 and 2006.
The new pictures show a handful of stars inside the small galaxy (circled in red above) that may be as much as ten billion years old. This puts I Zwicky 18 in the same age group as our own 12-billion-year-old Milky Way galaxy. What's more, the detailed images allowed researchers to see stellar "mile markers" that suggest the tiny galaxy is actually 59 million light-years away.
A paper on the discovery, led by Alessandra Aloisi of the ESA and the Space Telescope Science Institute, appeared in a recent issue of the Astrophysical Journal Letters.
Despite the revelation, astronomers are still excited by I Zwicky 18's unusual properties.
"Although the galaxy is not as youthful as was once believed," Aloisi said in a press statement, "it is certainly developmentally challenged and unique in the nearby universe."
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