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Under the above assumptions of incompressibility of the neutron etc., the neutron's density should be greater than or equal to that of the densest blackhole in the universe. Thus the radius of the (spherically assumed) neutron should be less than or equal to the critical radius at which the neutron just becomes a blackhole. The calculation should not be a problem, given the fact that the escape velocity at the surface of the neutron must equal the speed of light in vacuum.
r (critical) = 2 G M(neutron)/c**2.

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