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Last Updated: Tuesday, 7 December, 2004, 11:08 GMT
Hubble spots 'youngest galaxy'
I Zwicky 18 started active star formation about 13 billion years after the Big Bang

The Hubble Space Telescope has spotted what may be the youngest galaxy ever seen in the Universe.

The spring chicken may be as young as 500 million years old - so recent that complex life had already arisen on Earth by the time it started to bloom.

Called I Zwicky 18, it has provided astronomers with a rare glimpse into what the Universe's first diminutive galaxies might have looked like.

The finding is reported in the latest issue of the Astrophysical Journal.

At 12 billion years old, our own galaxy, the Milky Way, is over 20 times older.

This late bloomer, as viewed from Earth, seems to have undergone several sudden bursts of star formation; the earliest about 500 million years ago and the latest only 4 million years ago.

"I Zwicky 18 is a bona-fide young galaxy," said co-author Trinh Thuan, professor of astronomy at the University of Virginia, US.

Wispy filaments

Two major starburst regions can be seen as concentrated bluish-white knots embedded in the heart of the galaxy.

The wispy blue filaments are bubbles of gas that have been heated by stellar winds and intense ultraviolet radiation unleashed by hot, young stars.

The redder objects are slightly older stars and star clusters, but astronomers estimate they are still less than one billion years old.

The baby galaxy managed to lie in an embryonic state as a "nearly pristine" gas cloud of hydrogen and helium for most of the Universe's evolution. It did not begin active star formation until some 13 billion years after the Big Bang.

Star formation in the early Universe may have looked something like this

It is speculated that a companion galaxy, which lies just above and to the right, may have triggered star formation in I Zwicky 18.

Professor Thuan's co-researcher, Yuri Izotov, from the Kiev Observatory, Ukraine, called the finding "extraordinary".

"One would expect young galaxies to be forming only around the first billion years or so after the Big Bang, not some 13 billion years later," he said.

"Young galaxies were expected to be very distant, at the edge of the observable Universe, but not in the local Universe."

The young galaxy is located 45 million light-years away - much closer to other young galaxies in the nearly 14-billion light-year span of the Universe.

It is one of a catalogue of 30,000 nearby galaxies that Swiss astronomer Fritz Zwicky assembled in the 1930s by photographing the entire northern sky.

Though its primordial chemical make-up has long led astronomers to suspect I Zwicky 18 was a youngster, Hubble's sensitivity allowed astronomers to set an upper limit on the galaxy's age.

Astronomers capture galactic dance
13 Sep 04 |  Science/Nature
Stars reveal the Milky Way's age
17 Aug 04 |  Science/Nature
Hubble sights Milky Way's 'twin'
09 Aug 04 |  Science/Nature

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