We report the discovery of additional hot and massive stars in the cluster surrounding the soft gamma repeater SGR 1806 - 20 , based upon UKIRT and Keck near-infrared spectroscopy .
Of the newly identified stars , three are Wolf-Rayet stars of types WC8 , WN6 , and WN7 , and a fourth star is an OB supergiant .
These three stars , along with four previously discovered , imply a cluster age of \sim 3.0-4.5 Myr , based on the presence of WC stars and the absence of red supergiants .
Assuming coevality , this age suggests that the progenitor of SGR 1806 - 20 had an initial mass greater than \sim 50 M _ { \odot } .
This is consistent with the suggestion that SGRs are post-supernovae end states of massive progenitors , and may suggest that only massive stars evolve into magnetars that produce SGRs .
It also suggests that very massive stars can evolve into neutron stars , not just black holes , as recently predicted by theory .
The cluster age also provides constraints on the very high mass object , LBV 1806 - 20 .