  The standard model for Type II supernovae explosion, confirmed by the
detection of the neutrinos emitted during the supernova explosion, predicts the
formation of a compact object, usually assumed to be a neutron star. However,
the lack of the detection of a neutron star or pulsar formed in the SN 1987A
still remains an unsolved mystery. In this paper we suggest that the newly
formed neutron star at the center of SN1987A may undergo a phase transition
after the neutrino trapping time scale (~10 s). Consequently the compact
remnant of SN 1987A may be a strange quark star, which has a softer equation of
state than that of neutron star matter. Such a phase transition can induce the
stellar collapse and result in a large amplitude stellar oscillations. We use a
three dimensional Newtonian hydrodynamic code to study the time evolution of
the temperature and density at the neutrinosphere. Extremely intense pulsating
neutrino fluxes, with submillisecond period and with neutrino energy (> 30 MeV)
can be emitted because the oscillations of the temperature and density are out
of phase almost 180 degree. If this is true we predict that the current X-ray
emission from the compact remnant of SN 1987A will be lower than 10^34 erg s-1,
and it should be a thermal bremsstrahlung spectrum for a bare strange star with
surface temperature of around ~10^7 K.
