Gravitational radiation from supernova neutrino bursts

Abstract

SUPERNOVAE, the violent collapses of massive stars into neutron stars, are considered to be the strongest known sources of gravitational radiation. The quadrupole (and higher) moments of the hydrodynamic motions of the infalling matter generate the radiation. A burst of neutrinos of total energy ∼0.1 M⊙c² and of duration between ∼10⁻³ and 1 s is thought to accompany the collapse¹. If this burst has nonspherical angular distribution, it will generate additional gravitational radiation— possibly comparable in magnitude to that caused by the collapse. That the neutrino burst might produce gravitational waves had been overlooked until recently, when Epstein suggested the idea². This problem is of interest in its own right because a massless field is acting as the source of a radiation field. In electromagnetism there are no charged, massless particles; in fact, the existence of such a particle would lead to infrared divergences³. The gravitational effects of neutrinos have been studied previously^2,4–6, but the approach we report here is new and has a nice analogue in electromagnetism. The emission of a neutrino is a quantum process and so we use the zero frequency limit (ZFL) quantum technique of Weinberg³ to obtain a classical source which gives correct results in this limit. Because the time scale of the burst (∼10⁻³–1 s) is much longer than that of the neutrino emission process (∼10⁻²² s) only the ZFL is needed in the calculation. The ZFL technique has been used in an analogous way in electromagnetism to calculate the electromagnetic radiation accompanying β-decay or electron capture⁷. Smarr has applied the ZFL method to the gravitational bremsstrahlung process⁸.