From which stars black holes and neutron stars may form?

We discuss a problem of the formation of neutron stars and black holes from massive stars. It appears that several independent lines of evidence indicate that a considerable fraction of the stars more massive than 20-25 M. leave black holes as remnants, while, on the other hand, the neutron star in at least one High Mass X-ray Binary had a progenitor more massive than 50 M.. We suggest that if the collapsing core has a strong magnetic field and rotates rapidly it will produce a neutron star which expells the remaining matter of the star producing an observable Supernova, whereas if it is not strongly magnetized and/or is slowly rotating it collapses silently to a black hole. This model allows one to understand: (i) the large range in masses of the black holes in the soft X-ray transients (SXT), from about 3 M. to gt; 12 M. (ii) the fact that in some X-ray binaries of very high mass (gt; 50 M.) one still sometimes finds neutron stars, (iii) the observed fact that the birthrates of SXT with neutron stars and black holes are of the same order of magnitude and (iv) that galactic nucleosynthesis requires no contribution from stars more massive than 20-25 M qq.