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Missing galaxies puzzle scientists

Where'd all the plasma come from?

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The latest Ultra Deep Field images from Hubble, pictures of ancient, star -forming galaxies, have left scientists with a bit of a problem. There aren't nearly as many galaxies as theories predict there should be.

The analysis of Hubble's data was carried out by a team of UK researchers led by Dr Andrew Bunker at the University of Exeter and graduate student Elizabeth Stanway at the Institute of Astronomy at Cambridge University.

The researchers explain that at this very early point in the universe's history, the space between galaxies was filled with neutral gas. Something caused this gas to ionise rather rapidly (in astronomical terms) so that space was filled with plasma instead.

Ultraviolet light, produced by forming stars, is widely thought to have been the most likely trigger for the switch. By working out how much UV would be needed to ionise all the insterstellar gases, astronomers could calculate how many stars needed to form, to produce the radiation.

The answer is: there are more stars than could be produced in the galaxies they have found.

Hubble peered back in time using its infrared imaging system and built up an image of a patch of sky using multiple exposures.

Stanway explains that the visible light from these objects would have been absorbed by gas clouds long before it reached Earth: "but their infrared light can be detected, and it is their infrared colours which lead us to believe that these galaxies lie at such immense distances," she said.

The galaxies have a red shift of six, meaning they are around 13bn years old, and are some of the earliest star-forming galaxies ever detected. These stellar nurseries existed when the universe was just a billion years old, and are twice as old as our own solar system.

The astronomers used the Keck and Gemini telescopes (based in Hawaii and Chile) to verify their results.

"Using the largest optical telescope, Keck, was very important as it showed that this population of objects discovered by the Hubble Space Telescope really are incredibly distant", Bunker said.

There are a number of possible explanations for the findings, he told the BBC> One possibility is that the physics of the universe was different, and that our understanding of star formation is "flawed".

The puzzling results have been confirmed by other scientists working in the field, and will be published in the journal Monthly Notices of the Royal Astronomical Society.

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