Could the Most Luminous Supernova ASASSN-15lh Be Powered by a Newborn Rapidly-Rotating Strange Quark Star?

Strange quark stars (SQSs), consisting of quark matter with comparable numbers of deconfined up, down and strange quarks, have so far remained a hypothetical class of compact objects. Observationally, it is difficult to distinguish between SQSs and neutron stars (NSs), because both classes of stars have similar structural and cooling features for stellar masses above one solar mass. Here we show that the most luminous supernova discovered very recently, ASASSN-15lh, could have been powered by a newborn strongly-magnetized pulsar, which initially rotates near the Kepler limit. If this pulsar is a NS, its rotational energy could be quickly lost as a result of gravitational-radiation-driven r-mode instability. If it is a SQS, however, this instability is highly suppressed due to a large bulk viscosity associated with the nonleptonic weak interaction among quarks and thus most of its rotational energy could be extracted to drive ASASSN-15lh. Therefore, such an ultra-energetic supernova may provide a smoking gun signature for the birth of a SQS.