Upsetting Einstein's 'theory of gravity' is the headline at www.dailygalaxy.com/my_weblog/2017/03/andromeda-once-flew-past-our-milky... ... This follows research at the University of St Andrews (and elsewhere in Europe as it was a joint effort) which found a ring of small galaxies moving away from our galaxy at a faster rate than expected. They are expanding so rapidly it has been labelled a mini version of Big Bang. The paper suggests that our neighbouring galaxy, Andromeda, once flew past our Milky Way galaxy at close range. If Einstein was correct, they say, Andromeda would never have come so close, or be able to scatter smaller galaxies at such a fast rate. It is the ring like distribution of the small galaxies, described as a string of rain drops flung from a spinning umbrella, that caused the rethink. It is said there is just a 1 in 640 chance of this happening on a random basis. The author event calls it a tsunami wave in the sky, stirred up by the speeding Andromeda's near miss with the Milky Way.
Current interpretation of Einstein's theory of gravitation requires the addition of dark matter, we are told, but such a rapid speed requires 60 times the mass we see in the stars of Andromeda and the Milky Way which produces a problem. Friction between their two huge halos of dark matter could result in a merging of the two big galaxies - but why did they fly apart?
The idea they came close is of course a theory derived from modelling and it doesn't mean there was necessary a coming together as envisaged. It was a way to explain the fleeing at a fast clip of the small galaxies that came up with the idea of Andromeda almost colliding with our galaxy. However, we look at it, if these people are right does that mean Einstein's theory has been challenged - or is it the concept of dark matter that is under the spotlight?