How fast does dark matter fall?
Michael Kesden and Marc Kamionkowski Physical Review Letters (forthcoming article, available to journalists on request) Dark matter is mysterious stuff. Scientists don’t really know much about it at all, other than the fact that there seems to be a lot of it in the universe. Thanks to a new analysis by physicists at Caltech and the University of Toronto, we can expect that lumps of dark matter gravitationally attract each other in just the same way that lumps of normal matter (like you and the earth, for instance) attract each other. The researchers drew their conclusion by studying the distribution of stars in the Sagittarius dwarf galaxy that orbits our Milky Way. If dark matter experienced different forces from normal matter, it would change the relative amounts of stars kicked out ahead and behind the dwarf galaxy as a result of its interaction with our own galaxy. But the new study finds that the star distribution is just what we should expect if dark matter obeys the same gravita
