Is pulsar make up of strange matter? The magnetic field decay of a pulsar maybe able to give us an answer. Since Cooper pairing of quarks occurs inside asufficiently cold strange star, the strange stellar core is superconducting. Inorder to compensate the effect of rotation, different superconducting speciesinside a rotating strange star try to set up different values of London fields.Thus, we have a frustrated system. Using Ginzburg-Landau formalism, I solvedthe problem of rotating a superconducting strange star: Instead of setting up aglobal London field, vortex bundles carrying localized magnetic fields areformed. Moreover, the number density of vortex bundles is directly proportionalto the angular speed of the star. Since it is energetically favorable for thevortex bundles to pin to magnetic flux tubes, the rotational dynamics andmagnetic evolution of a strange star are coupled together, leading to themagnetic flux expulsion as the star slows down. I investigate this effectnumerically and find that the characteristic field decay time is much less than20~Myr in all reasonable parameter region. On the other hand, thecharacteristic magnetic field decay time for pulsars is $\geq 20$~Myr. Thus, myfinding cast doubt on the hypothesis that pulsars are strange stars.
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