High-resolution simulations of the head-on collision of white dwarfs

Abstract

The direct impact of white dwarfs has been suggested as a plausible channel\nfor type Ia supernovae. In spite of their (a priori) rareness, in highly\npopulated globular clusters and in galactic centers, where the amount of white\ndwarfs is considerable, the rate of violent collisions between two of them\nmight be non-negligible. Even more, there are indications that binary white\ndwarf systems orbited by a third stellar-mass body have an important chance to\ninduce a clean head-on collision. Therefore, this scenario represents a source\nof contamination for the supernova light-curves sample that it is used as\nstandard candles in cosmology, and it deserves further investigation. Some\ngroups have conducted numerical simulations of this scenario, but their results\nshow several differences. In this paper we address some of the possible sources\nof these differences, presenting the results of high resolution hydrodynamical\nsimulations jointly with a detailed nuclear post-processing of the nuclear\nabundances, to check the viability of white dwarf collisions to produce\nsignificant amounts of 56Ni. To that purpose, we use a 2D-axial symmetric\nsmoothed particle hydrodynamic code to obtain a resolution considerably higher\nthan in previous studies. In this work, we also study how the initial mass and\nnuclear composition affect the results. The gravitational wave emission is also\ncalculated, as this is a unique signature of this kind of events. All\ncalculated models produce a significant amount of 56Ni, ranging from 0.1 Msun\nto 1.1 Msun, compatible not only with normal-Branch type Ia supernova but also\nwith the subluminous and super-Chandrasekhar subset. Nevertheless, the\ndistribution mass-function of white dwarfs favors collisions among 0.6-0.7 Msun\nobjects, leading to subluminous events.\n