Mass-radius relations for the marginal values of n₁, for which stable twin branches can be formed, in the case of the DR and C EOS (colours correspond to the same parameters, except n₁ values, as shown in Fig. 13 and in Table 2). Thick lines correspond to the M_max (or R_min on the twins branches) for all ranges of n₁. The causal limit is shown as a dark shaded area, when the light shaded space corresponds to the photon orbit in the Schwarzschild case. Some stable configurations can be formed within the photon orbit. For the C EOS, when M_max is high, the quark phase occurs for very low masses.