2007MNRAS.381L...1L

The pulsar PSR B1828-11 has long-term, highly periodic and correlated variations in both pulse shape and the rate of slow-down. This phenomenon may provide evidence for the precession of the pulsar as suggested previously within the framework of free precession as well as forced. On a presumption of forced precession, we propose a quark planet model to this precession phenomenon instead, in which the pulsar is torqued by a quark planet. We construct this model by constraining the mass of the pulsar (M_psr), the mass of the planet (M_pl) and the orbital radius of the planet (r_pl). Five aspects are considered: the derived relation between M_psr and r_pl, the movement of the pulsar around the centre of mass, the ratio of M_psr and M_pl, the gravitational wave radiation time-scale of the planetary system, and the death-line criterion. We also calculate the range of the precession period derivative and the gravitational wave strength (at earth) permitted by the model. Under reasonable parameters, the observed phenomenon can be understood by a pulsar (∼10^–4-10^–1M_☉) with a quark planet (∼10^–8-10^–3M_☉) orbiting it. According to the calculations presented, the pulsar would be a quark star because of its low mass, which might eject a lump of quark matter (to become an orbiting planet) during its birth.