Once the motion of the star is known, and the mass of the compact object has been determined, scientists can deduce whether the invisible component is a black hole or a neutron star: the upper limit f...Once the motion of the star is known, and the mass of the compact object has been determined, scientists can deduce whether the invisible component is a black hole or a neutron star: the upper limit for the mass of a neutron star is about three times the mass of the Sun.