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dhani — October 25, 2007 / 10:56 pm
This picture shows an object known as I Zwicky 18, a dwarf irregular galaxy that first identified by Swiss astronomer Fritz Zwicky in a 1930s photographic survey of galaxies. Observations of this object at the Palomar Observatory around 40 years ago seemed to show that it was one of the youngest galaxies in the nearby Universe.
Yet, the latest observation with the Hubble Space Telescope shows that I Zwicky 18 seem to indicate that it is in fact much older and much farther away than previously thought. The telescope found fainter older red stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as 10 billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.
The new data suggest that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. On extragalactic standards this is still in our own backyard yet the galaxy’s larger-than-expected distance may now explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint old stars in I Zwicky 18 are almost at the limit of Hubble’s sensitivity and resolution.
Image credits: NASA, ESA and A. Aloisi (ESA/STScI)
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