We present that the appearance of hyperons plays a crucial role in failed supernovae from massive stars of ∼ 40 Mȯ. The quick dynamics from the gravitational collapse to the black hole leads to extreme conditions, reaching high densities and temperatures to have strangeness particles, within 1 s after the core bounce. The associated neutrino bursts are short and energetic, being different from ordinary supernova neutrinos, and may provide the information on the strangeness in dense matter. The end point of the duration of neutrino burst is determined by the stiffness of EOS and the appearance of new particle is the trigger of the termination due to the black hole formation. By measuring the duration of burst and the energy spectrum, one can constrain the appearance of exotics. The event numbers of neutrinos from the black-hole-forming collapse at the terrestrial detector are found large enough to utilize this phenomena as a target of neutrino astronomy and a probe of dense matter with strangeness.
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