Sterile neutrinos, shielded candles and modified gravity: cosmology looks beyond the standard model

Press/Media: Relating to Research


What are the mysterious dark matter and dark energy that seem to account for so much of our Universe? Why is the Universe expanding? For the past 30 years, most cosmologists have looked to the ‘standard model’ to answer these questions, and have had wide-ranging success in simulating formation in the universe and matching observational data.  But not everything quite fits the predictions. Are these discrepancies down to the interpretation of observations, or is a more fundamental rethink required? On Tuesday 7th July, a special session at the National Astronomy Meeting (NAM) 2015 has been convened for astronomers to take stock of the evidence and stimulate further investigation of cosmology beyond the standard model. 

However, not everyone believes that extra mass from dark matter is needed to explain observations. Indranil Banik and colleagues at the University of St Andrews believe that a modified theory of gravity may be the answer. Banik and colleagues have constructed a detailed model predicting velocities of galaxies in the local group, which is dominated by the mass of our own Milky Way and the neighbouring Andromeda galaxy.
“On large scales, our Universe is expanding – galaxies further away are going away from us faster. But on local scales, the picture is more confusing,” said Banik. “We found that running our model in the context of Newtonian gravity did not match the observations very well. Some local group galaxies are travelling outwards so fast that it’s as if the Milky Way and Andromeda are exerting no gravitational pull at all!”
The St Andrews group suggests that these fast-moving outliers could be explained by a gravitational boost from a close encounter between the Milky Way and Andromeda about 9 billion years ago. The very fast motions of the two galaxies as they flew past each other, at around 600 kilometres per second, would have caused gravitational slingshot effects on other galaxies in the local group.

Period9 Jul 2015

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