GW emission from merging strange quark star-strange quark planet systems

Abstract

Strange quark matter (SQM) may be the true ground state of hadronic matter. The observed pulsars may actually be strange quark stars, rather than neutron stars. With such an SQM hypothesis, researchers have predicted the existence of hydrostatically stable sequence of strange quark stars, like strange quark dwarfs and even strange quark planets. However, the SQM hypothesis is difficult to test due to the similarity between strange stars and neutron stars. Recently, we proposed a hopeful new method to probe the existence of SQM, which focuses on the study of strange quark planet systems. Strange quark planets will not be tidally disrupted even when they get very close to their host stars due to their extreme compactness. It is pointed out that one could identify strange quark planets by searching for very close-in planets among extra-solar planetary systems. Particularly, we should pay attention to possible pulsar planets with an orbital radius less than about 5.6 × 1010 cm and/or an orbital period less than about 6100 s. The pulsar planet of PSR J1719 − 1438 b, with an orbital radius of ∼ 6 × 1010 cm and orbital period of 7837 s, is encouragingly found to be a good candidate. Additionally, recent progresses in the field of gravitational wave astronomy encourages us to study gravitational waves emission from SQM planet systems. Strange quark planets can spiral very close to their host strange stars, and produce strong gravitational waves at the final merging stage. This kind of events can be detected by our current and upcoming gravitational wave detectors, such as the advanced LIGO and the Einstein Telescope.