PSR B1828-11 (also known as PSR B1828-10[2]) is a pulsar approximately 10,000 light-years away in the constellation of Scutum. The star exhibits variations in the timing and shape of its pulses: this was at one stage interpreted as due to a possible planetary system in orbit around the pulsar, though the model required an anomalously large second period derivative of the pulse times.[3] The planetary model was later discarded in favour of precession effects as the planets could not cause the observed shape variations of the pulses.[4][5] While the generally accepted model is that the pulsar is a neutron star undergoing free precession,[6] a model has been proposed that interprets the pulsar as a quark star undergoing forced precession due to an orbiting "quark planet".[7] The entry for the pulsar on SIMBAD lists this hypothesis as being controversial.[2]
