By combining high-resolution ( HST-WFPC2 ) and wide-field ground based ( 2.2m ESO-WFI ) and space ( GALEX ) observations , we have collected a multi-wavelength photometric data base ( ranging from the far UV to the near infrared ) of the galactic globular cluster NGC1904 ( M79 ) .
The sample covers the entire cluster extension , from the very central regions up to the tidal radius .
In the present paper such a data set is used to study the BSS population and its radial distribution .
A total number of 39 bright ( m _ { 218 } \leq 19.5 ) BSS has been detected , and they have been found to be highly segregated in the cluster core .
No significant upturn in the BSS frequency has been observed in the outskirts of NGC 1904 , in contrast to other clusters ( M 3 , 47 Tuc , NGC 6752 , M 5 ) studied with the same technique .
Such evidences , coupled with the large radius of avoidance estimated for NGC 1904 ( r _ { avoid } \sim 30 core radii ) , indicate that the vast majority of the cluster heavy stars ( binaries ) has already sunk to the core .
Accordingly , extensive dynamical simulations suggest that BSS formed by mass transfer activity in primordial binaries evolving in isolation in the cluster outskirts represent only a negligible ( 0–10 % ) fraction of the overall population .