On the viability of gravitational Bose-Einstein condensates as alternatives to supermassive black holes

Abstract

It is argued that astrophysical Bose-Einstein condensates (BECs) most likely form through a quasi-static contraction of ultradense cores of neutron stars. Such an evolutionary track would ensure that there is sufficient time left for the nuclear matter to stably liberate the excess of thermal energy, enable the core's matter to intercommunicate and undergo a phase transition to form stellar BECs. This slow contraction would enable their gravitational redshifts to be sufficiently high not to shine, but not too large to still escape collapse into black holes. The collapse can be made avoidable if the core's fluid is perfectly incompressible and noncontractible, not even on the scale of 10 −24 of a nanometre. It is shown that a slowly contracting core would maintain causal communication with the crust and it is preferable over the direct dynamical collapse of massive stars. In the latter case, the post-collapsed matter would be too energetic to enter a superfluidity phase and would turn the cores turbulent. Moreover, it is shown that super massive Bose-Einstein condensate (SMBEC) cores most likely would suffer from an extensive deceleration of their rotational frequency as well as of vortex dissipation induced by the magnetic fields threading the crust, hence accelerating the transition of cores into the BEC phase. Given that rotating superfluids between two concentric spheres have been verified to be dynamically unstable to non-axisymmetric perturbations, we conclude that gravitational forces generally govern astrophysical BECs, if these exist in nature, and would have a rather stabilizing effect, such as maintaining the perfect incompressibility of the nuclear matter.

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