There鈥檚 no need to invoke dark matter to explain why nearly 80 per cent of spiral galaxies have a bar of stars or dust running through them. A tweaked version of Newton鈥檚 law of gravitation does the job better.
Olivier Tiret and Fran莽oise Combes of the Paris Observatory used computer models to compare how the bars form, either with dark matter or modified Newtonian dynamics (MOND), in which gravity changes character as you get further away from a galaxy鈥檚 centre ().
Bars formed in a billion years in MOND models, but much more slowly with dark matter. Both models give roughly what is seen today, but MOND matches the frequency of bars more closely.
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