A Lonely Neutron Star . ... Credit Copyright: F. Walter ( SUNY Stony Brook ), WFPC2 , HST , NASA Explanation: How massive can a star get without imploding into a black hole? These limits are being tested by the discovery of a lone neutron star in space. Observations by the Hubble Space Telescope released Wednesday, have been combined with previous observations by the X-ray ROSAT observatory and ultraviolet EUVE observatory for the isolated star at the location of the arrow. ...