Thermonuclear explosions on neutron stars

Thermonuclear explosions of accreted hydrogen and helium on the surface of neutron stars, which are observed as type I-ray bursts, are the most frequent type of explosion in the galaxy and the third most energetic after supernovae and classical novae. They have been observed almost continuously since their discovery in 1976. However, during the past decade a new class of neutron star bursts, called superbursts, has been identified using BeppoSAX and RXTE data. According to theory superbursts are caused by deep and massive explosions of the carbon accumulated in the X-ray burst ashes. The problem is that detailed numerical X-ray burst simulations do not produce the required amount of carbon to satisfy this theory. In the talk, I present global studies of the behavior of the neutron star that theoretically restrict the reaction rate uncertainty based on astronomical observations. If this rate were just right, it would lead to copious generation of carbon. In addition, I discuss numerical models of the period following the superburst where X-ray bursts are quenched by the decaying thermal flux and massive amounts of carbon can be generated.