RX J1856 (aka RXJ185635-375) is a compact star that is suspected of being made of quark matter. It is theorized that the interior of the star is a gigantic atomic nucleus due to the fact that it appears much smaller than expected for a neutron star. This was announced as being discovered by the Chandra X-Ray Observatory on April 10, 2002.
The star lies at 18:56:35 right ascension -37 5 declination, using the J2000 coordinates.