X Ray Stars of 47 Tucanae . ... CXO , NASA . ... The x-ray stars here are double stars or "compact" binary star systems . They are so called because one of the pair of stellar companions is a normal star and the other a compact object -- a white dwarf , neutron star , or possibly a black hole . Chandra's x-ray vision detects the presence of an unexpectedly large number of these exotic star systems within 47 Tucanae , but it also indicates the apparent absence of a large central black hole. ...