Parity nonconservation and stellar collapse
ACCORDING to the current theory, the evolution of sufficiently massive stars leads eventually to gravitational instability and collapse. After thermonuclear burning has stopped, dense stellar cores become unstable and collapse to form neutron stars (pulsars) or black holes. In both cases energy of the order of 0.1 Mc2 is released, mostly in the form of neutrinos and gravitational waves. As the radius of the core decreases, its magnetic field grows (magnetic flux is conserved) and can reach huge values of order 1012–1013 G. Even greater azimuthal fields (∼3 × 1015 G) can be generated by differential rotation of the core1. It will be shown here that neutrino emission in the collapse is asymmetric, as a result of parity nonconservation in weak interactions. Neutrinos and antineutrinos are emitted preferentially in the direction parallel to the local magnetic field of the collapsing core.
Neutrino angular momentum losses in stellar collapse
WE know from observation that even the most rapidly rotating neutron stars—those of the Crab and Vela—are slow rotators, in the sense that their angular momentum is of negligible structural importance. In fact, at least for these pulsars, estimates based on their current slowdown rates indicate their rotation frequencies at birth were probably only a few times higher than the present ones1, even though the main sequence progenitors probably had much more angular momentum per unit mass. The purpose of the present note is to examine the degree to which one can attribute such a decrease in the angular momentum per unit mass to neutrino radiation emitted during the formation of the neutron star from the collapse of a sufficiently massive stellar core.
Vertebral Fusion in Two Early Jurassic Sauropodomorph Dinosaurs from the Lufeng Formation of Yunnan, China
Here we describe two instances of pathological vertebral fusion in two genera of sauropodomorph dinosaurs from the Early Jurassic Lufeng Formation in Yunnan, China. The first is a specimen, of Lufengosaurus huenei with two fused cervical vertebrae, and the other is a specimen of the Lufeng basal sauropod, with two fused caudal vertebrae. Both pathologies are consistent with spondyloarthropathy and represent the earliest known occurrence of that disease in dinosaurs. The two specimens affirm that early dinosaurs suffered from the same bone diseases as living vertebrates. Spondyloarthropathy in these dinosaurs may have been induced by long-term mechanical stress, such as weight bearing, and/or limited motion at the joint that would otherwise have inhibited such remodeling. In both cases, surface remodeling suggests that the animals survived well beyond the initiation of spondyloarthropathy.