LJMU astronomers throw new light on distant galaxies
26 April 2012
Current research from LJMU's Astrophysics Research Institute (ARI) sheds light on two of the biggest unanswered questions in astronomy – how the contents of the Universe were formed and the nature of dark matter.
By looking into deep space some 90% of the way back to the Big Bang, postgraduate student Claire Burke and her supervisor Professor Chris Collins have discovered significant amounts of starlight from regions surrounding the largest galaxies. This could help explain the question of why galaxies appear to grow quicker than current cosmological theories using dark matter and dark energy allow.
Claire comments: “When we look far back in terms of distance we are also looking back in time and the galaxies we are examining are 90% of the way back to the Big Bang, when the Universe was only a few billion years old (the age of the Universe now is nearly 14 billion years old). We compare what we see in these distant galaxies to others we see nearby to try to determine how these objects have evolved and changed over time. By doing this we can effectively 'wind back the clock' on the evolution of structure in the Universe. We have found that, surprisingly, the largest galaxies at these cosmological distances are as big and as heavy as their counterparts in the local Universe, so they must have grown very quickly in the early Universe and not undergone much change in the past nine billion years.”
But this raises a very difficult problem for theories dominated by dark matter and dark energy which predict that young galaxies should be small so soon after the Big Bang, growing slowly over time and reaching their current size only in the last three or four billion years.
Chris Collins, who is leading the research, comments:
"Why these galaxies appear to be so big at such an early time is a question that has troubled us for some years. It is like having your child grow to adult size by the time they are four or five – it just shouldn’t happen so soon."
However, in a recent breakthrough, the LJMU team and their collaborators from Universities of Durham and Nottingham now think they may have cracked the problem. From a careful analysis of new observations taken on the Very Large Telescope in Chile, they have made an unexpected detection of faint starlight surrounding the distant galaxies. The light appears to be coming from stars between the galaxies in the densest regions of space called galaxy clusters. The light is hard to detect because it is spread out over a region approximately two million light years across but the integrated effect is huge and the total light from this can be almost as bright as the largest galaxies themselves.
Chris Collins adds:
"Cluster halo light has been known about for decades but this is the first time anyone has had the audacity to search for it around galaxies so far back in time and it appears to have paid off."
This light between galaxies is thought to be the remnant of colliding galaxies devouring each other and leaving just a faint halo of starlight surrounding a large central cluster galaxy. Crucially this light has not been tagged in the cosmological computer simulations, which predict the growth rate of galaxies in clusters. This new data will help theorists 'tweak' their computer code to include this diffuse starlight component and produce new predictions, which it is hoped will agree better with the observations.
Even if this is successful, there is at least one more question that the team is determined to answer – how much dark matter is locked up in these distant galaxies? To answer this they are using another giant eight metre telescope called GEMINI, located in Hawaii, to find the total mass of these central cluster galaxies, including the dark matter. This can’t be seen by examining the light from galaxies in the normal way. The team will measure the speed of the stars as they orbit around the centre of the galaxy, and in this way they can measure the total gravitating mass of the galaxy.
"It is like spinning a conker on a string above your head, you have to keep a tight hold of the string or the conker will fly off; similarly when the stars orbit around the galaxy, gravity must hold them there or they would fly off into space. By measuring how fast the stars are orbiting we can directly measure how much dark matter is in the galaxy providing the gravitational force which holds onto the stars."
The findings of the ARI's research were presented at the National Astronomy Meeting in Manchester in March and are due to be published in Monthly Notices of the Royal Astronomical Society.