24 September 2004
Puzzle Over Low Galaxy Count
by Kate Melville
Scientists from the University of Cambridge and the University of Exeter are suggesting that the evolution of the early Universe was much slower than previously thought.
Doctor Andrew Bunker has been studying images taken by the Hubble Space Telescope of what is called Hubble's Ultra Deep Field (HUDF). Images from HUDF provide mankind's deepest optical view of the Universe in its earliest stages. Bunker and fellow researchers viewed the number of star-forming galaxies from these images and found that there were far less than expected. The rate at which new stars were born was a lot slower than formerly thought.
The HUDF images allowed Bunker's team to see almost to the beginning of time. They were able to identify 50 objects likely to be galaxies so far away that light from them has taken 13 billion years to reach the earth. The galaxies uncovered by the team existed 95% of the way back to the beginning of time. This is the closest man has ever come to the Big Bang, when the Universe was less than a billion years old.
"We can measure how fast stars are being born in the early universe," said Dr. Bunker. "But our results reveal a puzzle; the birth rate seems low compared with more recent pasts. This is not what theorists had expected: at early times, the Universe seems to undergo a rapid heating. The main candidate for what caused this is ultraviolet radiation, which can be generated as stars are born. Our results suggest this was not the case, the small number of star forming galaxies found in the Ultra Deep Field may not be sufficient to do this. Perhaps this heating happened further back in time, closer to the Big Bang."