Population synthesis of neutron stars, strange (quark) stars and black   holes
  We compute and present the distribution in mass of single and binary neutron stars, strange stars, and black holes. The calculations were performed using a stellar population synthesis code. We follow all phases of single and binary evolution, starting from a ZAMS binary and ending in the creation of one compact object (neutron star, black hole, strange star) and a white dwarf, or two compact objects (single or binary). We assume that neutron stars are formed in the collapse of iron/nickel cores in the mass range M0 < M < M1, quark stars in the range M1 < M < M2, and black holes for core masses M > M2 and find that the population of quark stars can easily be as large as the population of black holes, even if there is only a small mass window for their formation. 
Krzysztof Belczynski, Tomasz Bulik, Wlodzimierz Kluzniak