‘Extinct’ galaxy stuns astronomers

By AAP with AG Staff 7 October 2010
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A galaxy thought only to exist at the beginning of the Universe has been discovered by Australian scientists.

A TEAM OF AUSTRALIAN scientists has discovered a type of galaxy thought to be long gone in the Universe, shaking up existing theories on star formation. Swinburne University astronomy student Andy Green, his supervisor Professor Karl Glazebrook and their colleagues made the discovery using two telescopes at the Siding Springs observatory in NSW.

“We didn’t think these galaxies existed. We’ve found they do, but they are extremely rare,” says Karl. Galaxies like these have been seen before in the early Universe, around
three billion years after the Big Bang where they were quite common, but
this is the first time they have been found in today’s Universe.

The galaxies are similar to our own Milky Way, in their spiral disc-like shape, yet are in the process of forming far more stars, around 100 per year compared to just one per year in our galaxy.  These galaxies are also far more physically turbulent than our own relatively quiet neighbourhood, the scientsists say. They are found around one billion light-years from Earth, and although this means the events observed occurred one billion years in the past, they are considered relatively recent in the nearly 14 billion-year-old Universe.

The research is published today in the journal Nature, where an image of the gallery features on the cover.

Where does the gas come from?

The formation of stars is still one of the great questions of astronomy.
Stars are formed when large clouds of gas collapse under the weight of their own gravity and astronomers had proposed, says Karl, that “the extremely
fast star formation in those ancient galaxies was fuelled by a special
mechanism that could exist only in the early Universe – cold streams of
gas continually falling in.”

But the new discovery means that star formation
must have occurred any another means. “The problem now is that these galaxies we have observed are in the
modern Universe, where we don’t expect that primordial gas to be
available anymore, as most of it should have already been swept up into
other galaxies,” Andy says.

This raises the question: where is this gas coming from? If it can’t be coming from intergalactic space, then there must be some other explanation. “The other big potential theory is that the gas – rather than flowing smoothly into the galaxies – is accreted through clumps or small, almost mini-galaxies that are swallowed whole.”

Andy says this theory has the advantage of fitting better into the modern Universe as these clumps or dwarf galaxies are found today. The violent nature of a dwarf galaxy being merged with a large one may also explain the increased turbulence the team has observed.

Click here to see an animation of the galactic turmoil that forms a galaxy like the one pictured below (Swinburne University).