New Scientist: Galaxy study hints at cracks in dark matter theories. (Hat tip: Anaconda)
Dark matter is either weirder than we thought or does not exist at all, a new study suggests.
A galaxy is supposed to sit at the heart of a giant cloud of dark matter and interact with it through gravity alone. The dark matter originally provided enough attraction for the galaxy to form and now keeps it rotating. But observations are not bearing out this simple picture.
Since dark matter does not radiate light, astronomers infer its distribution by looking at how a galaxy's gas and stars are moving. Previous studies have suggested that dark matter must be uniformly distributed within a galaxy's central region – a confounding result since the dark matter's gravity should make it progressively denser towards a galaxy's centre. ...
"There is absolutely no rule in physics that explains these results," says study co-author Hong Sheng Zhao of the University of St Andrews in the UK.
... they say our understanding of gravity may need modification to eliminate the need for dark matter entirely.