Young Galaxies

A few years ago (around 1995) the Hubble Space Telescope stared at one apparently empty part of the sky in Ursa Major for around 125,000 seconds in order to look for very faint objects. The resulting Hubble Deep Field (HDF) through up a few thousand beautiful galaxies that nobody had seen before. A few years later, in 2004, the Hubble Ultra Deep Field (HUDF) was released which did a similar thing but had a total exposure time of around 1 million seconds. Just think about that for a moment; that is about 11 and a half days solid staring at the same point. Needless to say, it makes a pretty spectacular image.

Now, astronomers analysing the HUDF have identified over 500 galaxies that we see at a time when the Universe was less than a billion years old. That may seem like quite an age but compared to the current age - 13.7 billion years - that is effectively the early childhood of the Universe. These galaxies tend to look like rather unexciting red blobs but are actually very blue dwarf galaxies with lots of stars being formed within them. They appear red in the Hubble images because their light has been redshifted by the expansion of the Universe in the 13 billion years or so that it took the light from them to reach us.

HUDF
Hubble Space Telescope image showing 28 of the more than 500 young galaxies that existed when the universe was less than 1 billion years old. CREDIT: NASA, ESA, R. Bouwens and G. Illingworth (University of California, Santa Cruz, USA)

The measurements also show that there was around 10 times the amount of star formation back then as we see in nearby galaxies today. That suggests that there may have been enough light being emitted to reheat the hydrogen gas that had been cooling since the big bang.

Hubble continues to produce lots of great science so I just hope the Hubble servicing mission goes ahead to keep things going until the James Webb Space Telescope is launched.

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Posted in astro blog by Stuart on Thursday 21st Sep 2006 (19:34 BST) | Permalink
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