RX J1856: Astrophysical evidence for quark stars

On 10 April 2002 NASA announced that Chandra observations of the compact object RX J185635-3754 implied that it was smaller than allowed by models of neutron stars, and that this was evidence for the existence of quark stars. If true, this is a very important observation. But the bulk of the evidence does not support this assertion. I shall review the extant data, and show that neither the data nor theory supports this interpretation. On the other hand, the data show that compact objects may be far stranger than we thought.