Dropping Dark Matter

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, published this week in Physical Review Letters, 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 (pictured here, courtesy of NASA’s image archive) 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 gravitational laws as regular matter, to within an error of 10%. Future observations and improvements in our understanding of dark matter distributions should reduce the uncertainty to a few percent.

The analysis helps eliminate astrophysical models that explain the distribution of material in the universe by proposing exotic forms of gravitational interactions for dark matter. In addition, despite the fact that there is broad speculation regarding the true identity of dark matter and no guarantee that we will ever capture it or produce it in the lab, at least we now know how long it will take to reach the floor if a resident of a dark matter planet were to knock a bit of it off of a table.

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