Dark matter returns

A few weeks back I wrote a post entitled “Where is our dark matter?” As you’ll recall, a team of astronomers analysed the motion of 412 stars at a distance of 1 to 4 kpc from the midplane of the Galaxy and derived a local density of dark matter that was ten times less than models suggest should be there. It was a puzzle.

Well, the puzzle might have been solved. Jo Bovy and Scott Tremaine of the Princeton Institute for Advanced Study have recently posted a paper on arXiv called “On the local dark matter density“. Bovy and Tremaine argue that the authors of the first paper made an incorrect assumption about the average rotational velocities of the objects they studied. When that assumption was replaced by a correct assumption about stellar velocities (an assumption, in other words, supported by data), Bovy and Tremaine found that lots of dark matter is there in the solar neighbourhood!

The dark matter paradigm survives another test. Let’s just hope that direct detection of dark matter happens soon.