WHAT lies at the very centre of the Galaxy -- that point about which the entire Milky Way turns? One way to answer the question is to look at the movements of stars in its vicinity. The first direct measurements of the proper motion of stars near theGalactic Centre are reported by Eckart and Genzel on page 415 of this issue. When combined with the best and most recent radial velocity data, they show with little ambiguity that about 2.5 million solar masses of dark matter lurks within a relatively tiny region at the centre.
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