Did Andromeda crash into the Milky Way 10 billion years ago?
Posted: Thu Jul 04, 2013 5:05 pm
Perhaps the title of the article should read "A Revisionist History of the Universe"? Interesting article to say the least. There are plenty of mergers to apply this new model to. I'd like to see a simulation!(Phys.org) —For many years scientists have believed that our Galaxy, the Milky Way, is set to crash into its larger neighbour, the Andromeda Galaxy, in about 3 billion years' time and that this will be the first time such a collision has taken place. But now a European team of astronomers led by Hongsheng Zhao of the University of St Andrews propose a very different idea; that the two star systems collided once before, some 10 billion years ago and that our understanding of gravity is fundamentally wrong.
Most cosmologists believe that across the whole universe, this matter outweighs 'normal' matter by a factor of five. The dark matter in both Andromeda and the Milky Way then makes the gravitational pull between the two galaxies strong enough to overcome the expansion of the cosmos, so that they are now moving towards each other at around 100 km per second, heading for a collision 3 billion years in the future.
But this model is based on the conventional model of gravity devised by Newton and modified by Einstein a century ago, and it struggles to explain some properties of the galaxies we see around us. Dr Zhao and his team argue that at present the only way to successfully predict the total gravitational pull of any galaxy or small galaxy group, before measuring the motion of stars and gas in it, is to make use of a model first proposed by Prof. Mordehai Milgrom of the Weizmann Institute in Israel in 1983.
This modified gravity theory (Modified Newtonian Dynamics or MOND) describes how gravity behaves differently on the largest scales, diverging from the predictions made by Newton and Einstein.
If gravity conforms to the conventional model on the largest scales then taking into account the supposed additional pull of dark matter, the two galaxies would have merged.
In the new model, the Milky Way and Andromeda are still going to crash into each other again in the next few billion years, but it will feel like 'deja vu'. And the team believes that their discovery has profound consequences for our current understanding of the Universe. Pavel Kroupa concludes, "If we are right, the history of the cosmos will have to be rewritten from scratch."
Read more at: http://phys.org/news/2013-07-andromeda- ... s.html#jCp