Clearing the cosmic fog

As the BBC noted, astronomers using ESO’s Very Large Telescope [VLT] have confirmed that galaxy UDFy-38135539, one of several candidates identified in the Hubble Ultra Deep Field (UDF) image of the Fornax Constellation acquired with the telescope’s new Wide Field Camera 3 last year, is the most distant galaxy ever detected. [Image credit: NASA, ESA, G. Illingworth (UCO/Lick Observatory and University of California, Santa Cruz) and the HUDF09 Team]

Spectroscopic analysis of data collected during a 16 hour observation using the VLT identified a red shift of 8.6, which corresponds to a galaxy seen just 600 million years after the Big Bang.  That’s even further back in time than Gamma Ray Burst 090423 – which I mentioned here.

Here’s an ESOcast on the subject of the most distant galaxy ever measured.

[Video credit: ESO. Visual design and editing: Martin Kornmesser and Luis Calçada.  Editing: Herbert Zodet. Web and technical support: Lars Holm Nielsen and Raquel Yumi Shida.  Written by: Richard Hook and Douglas Pierce-Price.  Narration: Dr. J. Music: movetwo.  Footage and photos: ESO, NASA, ESA, G. Illingworth  (UCO/Lick Observatory and University of California, Santa Cruz) and the HUDF09 Team, A. M. Swinbank and S. Zieleniewski, M. Alvarez (, R. Kaehler and T. Abel and José Francisco Salgado (  Directed by: Herbert Zodet.  Executive producer: Lars Lindberg Christensen.]

The research paper which appears in Nature is available here [pdf file].

As the accompanying text to the above image adds [Image credit: M. Alvarez (, R. Kaehler, and T. Abel]

At this early time, the Universe was not fully transparent and much of it was filled with a hydrogen fog that absorbed the fierce ultraviolet light from young galaxies. The transitional period when the fog was still being cleared by this ultraviolet light is known as the era of reionisation, illustrated with this still from a representative scientific simulation (see Alvarez et al. (2009) for more details).

When the Universe cooled down after the Big Bang, about 13.7 billion years ago, electrons and protons combined to form neutral hydrogen gas. This cool dark gas was the main constituent of the Universe during the so-called Dark Ages, when there were no luminous objects. This phase eventually ended when the first stars formed and their intense ultraviolet radiation slowly made the hydrogen fog transparent again by splitting the hydrogen atoms back into electrons and protons, a process known as reionisation. This epoch in the Universe’s early history lasted from about 150 million to 800 million years after the Big Bang. In this visualisation, ionised regions are blue and translucent, ionisation fronts are red and white, and neutral regions are dark and opaque.

The new study shows that the glow from UDFy-38135539 seems not to be strong enough on its own to clear out the hydrogen fog. There must be other galaxies, probably fainter and less massive nearby companions of UDFy-38135539, which also helped make the space around the galaxy transparent.

And finally, here’s a quick zoom through images from the Hubble Ultra-Deep Field towards UDFy-38135539.  [Video credit: A. M. Swinbank and S. Zieleniewski, Music: movetwo.]

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