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Tuesday, November 9, 2010

Ancient galaxy is more than 13 billion light years away

Ancient galaxy is more than 13 billion light years away
PARIS (AFP) - – European astronomers on Wednesday said a galaxy born in the childhood of the Universe lies at least 13 billion light years away, making it the remotest object ever observed.
Light from the galaxy UDFy-38135539 that reaches Earth today was emitted when the cosmos was only 600 million years old and mired in a primordial "fog" of hydrogen atoms, they said.
It has taken 13.1 billion years, travelling at 300,000 kilometres (186,000 miles) per second, for this smudge of infant light to arrive.
The study, appearing in the British journal Nature, used a giant European telescope in Chile's Atacama desert to measure the galaxy's so-called redshift.
The more distant a light source is, the longer its wavelength stretches. In other words, a light that appears to be receding from the observer shifts more towards the red part of the optical spectrum.
In this case, the galaxy's redshift was 8.6, making it the most distant object ever observed by spectroscopy.
The previous documented record, in 2009, was a redshift of 8.2 caused by a gamma-ray burst of a super-massive star. An object at a redshift of 10 was once reported but has never been confirmed.
"Measuring the redshift of the most distant galaxy so far is very exciting in itself, but the astrophysical implications of this detection are even more important," said Nicole Nesvadba of France's Institut d'Astrophysique Spatiale.
"This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early Universe."
Under the "Big Bang" theory, the Universe originated in a superheated-flash around 13.7 billion years ago and started to expand.
After the cosmos had cooled a little, electrons and protons teamed up to form hydrogen, which for hundreds of millions of years filled the Universe.
During this epoch, known as the Universe's "Dark Ages," there were no stars. It was followed by a period known as reionisation, in which the first stars formed and their intense ultra-violet radiation managed to pierce the hydrogen fog.
Understanding reionisation would also help to explain the formation of the first galaxies. But the starlight needed for evidence has -- until now -- been absent because of the opaque mist that shrouded the Universe at this time.
One theory is that the light from the newly-discovered galaxy was able to penetrate the fog because it was helped by other, nearby galaxies.
"Without this additional help, the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog and we would not have been able to detect it," said astronomer Mark Swinbank of Durham University, northeast England.
UDFy-38135539 -- whose name comes from its location in the "Ultra Deep Field" zone of deep space -- was first spotted last year by the US orbital telescope Hubble.
The dim light intrigued astronomers poring over the reionisation enigma, said lead author Matt Lehnert of the Observatoire de Paris.
They begged the boss of the European Southern Observatory (ESO) to give them special time on the Very Large Telescope (VLT), which has a highly sensitive redshift-measuring spectroscope.
Sixteen hours of observation, using a very long exposure time, enabled a clearer image of the galaxy, but two months of analysis and testing were needed to confirm the data.
In terms of distance, the gap between Earth and the galaxy is likely to be far higher than 13 billion light years, ESO told AFP.
This is because the Universe has been expanding since the time when the light was first emitted. As a result, the light has had to travel longer in order to "catch up" with us.


Source: http://sg.news.yahoo.com/afp/20101021/tts-space-astronomy-galaxy-c1b2fc3.html

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