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An international team of astronomers

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using ESO’s Very Large Telescope

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has measured the distance to the most remote galaxy so far.

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This is the first time that astronomers have been able to confirm

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that they are observing a galaxy as it was in the era of reionisation

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when the first generation of brilliant stars

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was making the young Universe transparent

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and ending the cosmic Dark Ages.

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This is the ESOcast!

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Cutting-edge science and life behind the scenes at ESO,

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the European Southern Observatory.

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Exploring the ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske.

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Hello and welcome to the ESOcast.

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In this episode we are going to find out how a team of astronomers

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used ESO’s Very Large Telescope, the VLT,

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to confirm that a galaxy that had previously been spotted

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in images from the NASA/ESA Hubble Space Telescope

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is in fact the most distant object that has ever been identified in the Universe.

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Studying these first galaxies is extremely difficult.

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They are very faint and small

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and by the time their dim light gets to Earth

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it falls mostly in the infrared part of the spectrum

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because it has been stretched by the expansion of the Universe.

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To make matters worse, at this very early time,

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less than a billion years after the Big Bang,

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the Universe was not completely transparent.

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It was filled with hydrogen which acted kind of like a fog

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and absorbed the ultraviolet radiation from the young galaxies.

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So, holding the record for having measured the redshift

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of the most distant object in the Universe

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is not just a trophy to hang on the wall,

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it does have important astrophysical implications.

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This is the first time that we’ve managed to obtain spectroscopic observations 

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of a galaxy from the era of reionisation,

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in other words from the time when the Universe

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was still clearing out the hydrogen fog.

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Despite the difficulties of finding these early galaxies,

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the new Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope

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discovered several very good candidate objects earlier in 2010.

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They were thought to be galaxies shining in the early Universe

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at redshifts greater than eight,

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but confirming the distances to such faint and remote objects

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is an enormous challenge

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and can only reliably be done using spectroscopy

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from very large ground-based telescopes.

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The team was excited to find that

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if you combine the huge light collecting power of the VLT,

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with the sensitivity of its infrared spectroscopic instrument, SINFONI,

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and if you then use a very long exposure time

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you just might be able to detect the faint glow

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from one of these very remote objects

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and then go on to measure its distance.

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A 16 hour exposure with the VLT and SINFONI

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of the galaxy UDFy-38135539

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did indeed show the very faint glow from hydrogen at a redshift of 8.6,

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which means that this light left the galaxy

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when the Universe was only about 600 million years old.

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This is the most distant galaxy ever reliably confirmed.

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One of the puzzling things about this discovery

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is that the ultraviolet radiation emitted by the galaxy

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does not actually seems to be strong enough

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to be able to clear out the hydrogen fog around the galaxy.

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So one possible explanation is that there must be other galaxies,

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probably fainter and less massive neighbours,

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that helped ionise the hydrogen in the region of space around the galaxy,

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thus making it transparent.

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Without this additional help 

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the brilliant light from the main galaxy

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would have been trapped in the surrounding hydrogen fog

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and it could not have even started its 13-billion-year journey towards Earth.

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Studying the era of reionisation

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and the formation of the first galaxies

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is really pushing the capabilities

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of current telescopes and instruments to the limit.

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But, this will be exactly the type of science

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that ESO’s European Extremely Large Telescope will excel at.

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Once operational,

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this will be the largest optical and infrared telescope in the world.

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This is Dr J signing off for the ESOcast.

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Join me again next time for another cosmic adventure.

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ESOcast is produced by ESO, the European Southern Observatory.

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ESO, the European Southern Observatory, is the pre-eminent intergovernmental science and technology organisation in astronomy

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designing, constructing and operating the world’s most advanced ground-based telescopes.

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Transcription by ESO ; translation by —

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Now that you've caught up with ESO,

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head 'out of this world' with Hubble.

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The Hubblecast highlights the latest discoveries

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of the world's most recognized and prized space observatory,

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the NASA/ESA Hubble Space Telescope