Astronomers spot farthest-known galaxy | Science| In-depth reporting on science and technology | DW | 21.10.2010
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Astronomers spot farthest-known galaxy

Using the Very Large Telescope (VLT) in Chile, a European research team has detected light from the most distant galaxy ever seen - dating back to less than 600 million years after the Big Bang.

A simulation of galaxies during the era of re-ionization

600 million years after the Big Bang, the universe was in its 're-ionization' phase

In a paper published Wednesday in the journal Nature, a European research team reported that the newfound galaxy UDFy-38185539 is the remotest cosmic object ever recorded. Studying it further will hopefully give astronomers a look back at the early days of the universe.

A European research team used an advanced telescope located on Cerro Paranal in Chile to spot light from the galaxy, which was emitted less than 600 million years after the Big Bang occurred more than 13 billion years ago.

"The interesting thing is that the universe at that moment is vastly different than what it is like now, or five or six billion years ago," said lead author Matthew Lehnert of the Paris Observatory in an interview with Deutsche Welle.

After the Big Bang, it took about one billion years for the universe to undergo a period of hydrogen re-ionization, which was driven by energetic objects in the cosmos. Until then, a neutral hydrogen fog absorbed a great deal of galactic light – signifying the "Dark Ages" of the universe.

Six-hundred million years ago, when light from UDFy-38185539 was filtering through this hydrogen haze, the re-ionization process was not yet complete - meaning the latest observations offer a glimpse into the "epoch" of the universe.

"It gives you insight into how galaxies formed under vastly different conditions," Lehnert added.

The infrared image taken by the Hubble Space Telescope in 2009

The galaxy 'UDFy-38135539,' shown when the universe was less than 600 million years old

The European Southern Observatory granted the team 16 hours of observation time – or two nights – with the Very Large Telescope (VLT), high in the mountains of Chile. Lehnert said an expert observer was responsible for collecting the data, which was then imported into an archive and downloaded by the team over a two-month period.

Meanwhile, the astronomers suspect that the far-flung UDFy-38185539 galaxy is not alone: the team's report suggests that other undiscovered sources in the surrounding area also had a hand in re-ionizing the universe.

A NASA astronaut works to upgrade the Hubble Space Telescope

A camera on the Hubble telescope allowed for "deep-field" images

Deep in the cosmos

Observing these so-called "deep-field" galaxies at such great distances was made possible by upgrades to the Hubble Space Telescope, which were completed in 2009.

A new infrared camera yielded data that allowed five research teams to identify potential "candidate" galaxies from the period just after the creation of the universe more than 13 billion years ago.

Using this research as a jumping-off point, Lehnert's group sought to confirm the existence of a galaxy located at a "redshift" value corresponding to a timeframe 600 million years after the Big Bang.

A team led by Ross McLure of the Institute for Astronomy at Edinburgh University was among those who initially detected the existence of UDFy-38185539 by analyzing the Hubble data.

McLure told Deutsche Welle that the spectral Lehnert's team observed at 8.5 on the redshift confirmed his team's own estimates of 8.4 - but that questions remained.

"I wouldn't say that it's 100 percent convincing on its own, and I think it will take further observation to actually confirm to everybody's satisfaction that the redshift is actually reliable for this object," he said.

The four main units for the Very Large Telescope (VLT) in Paranal

Astronomers used the VLT facility to catch a glimpse of the far-flung galaxy

Above the noise

Lehnert's team located the galaxy by detecting the Lyman-alpha spectral line, caused by the emission of hydrogen gas – but took pains to ensure that "noise" from the instrument and elements between the galaxy and Earth did not contaminate their findings.

McLure said the astronomers appeared to have thoroughly ruled out other possibilities - such as the presence of an emission line caused by oxygen, which would indicate the presence of a younger galaxy.

"The problem is that these objects are incredibly faint, of course, and they're very much at the limit of what you can detect in a spectrum with the VLT," he said, and added that the result is often "noisy" data.

Yet the team's paper concludes that the size of the emission line and its spectral width suggested a "source of astrophysical origin" - whereas a "noisy" result would correspond to a smaller line width.

Among the sources of potential contamination are night sky lines, which astronomers must remove.

"Getting rid of them in the data is not very easy, so you have to be very, very, careful," said Nicole Nesvadba of the Institute of Spatial Astrophysics in France, another one of the paper's authors, in an interview with Deutsche Welle.

Despite the challenges, researchers were pleasantly surprised.

"We never expected to be able to observe this with present-day telescopes," she said.

The James Webb Space Telescope is planned for 2014

The next generation of telescopes will facilitate future research

Looking ahead

Current observations are driving the construction of new generations of telescopes that could allow researchers to detect "dozens or maybe hundreds" of similar galaxies, Nesvadba added.

"We're in a much better position of planning these instruments," she said.

Meanwhile, Mark Swinbank, another author from Durham University in the United Kingdom, acknowledged the current constraints of the team's research, as well as the high burden of proof to authenticate the galaxy's signature.

"We're really pushing the limits of technology here," he told Deutsche Welle - saying the next step would be to observe the galaxy again using a different telescope, to "unambiguously prove" the result.

His team was working to confirm one of the universe's most far-flung galaxies, but Swinback said some of the impetus behind their research was also rooted in understanding things closer to home.

"The reason we do this is that what we want to do - ultimately - is to know about our own place in the universe," he said.

Author: Amanda Price
Editor: Cyrus Farivar

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