Spin--Down Power in Astrophysics

While the accretion power in astrophysics has been studied in many astronomical environments, the ``spin--down power'' is often neglected. In this essay I demonstrate that the spin--down power alone may drive a rotating system from sub-critical condition to critical condition with a small but finite probability. In the case of an isolated spinning-down neutron star, the star may undergo a quark--hadron phase transition in its center and become observable as a soft gamma repeater or a cosmological gamma--ray burst. For a spinning--down white dwarf, its Chandrasekhar mass limit will decrease and may reach the stellar mass, then the star explodes to a type Ia supernova. Gravitational wave detectors may be able to test these models.