On Type Ia Supernovae From The Collisions of Two White Dwarfs

TLDR: In this article, Maoz et al. explored collisions between two white dwarfs as a pathway for making Type IaSupernovae (SNIa) and found that such collisions produce 0.4 M of 56 Ni, making such events potential candidates for underluminous SNIa or a new class of transient between Novae and SNIA.

Abstract: We explore collisions between two white dwarfs as a pathway for making Type IaSupernovae (SNIa). White dwarf number densities in globular clusters allow 10 100redshift . 1 collisions per year, and observations by (Chomiuk et al.2008) of globularclusters in the nearby S0 galaxy NGC 7457 have detected what is likely to be a SNIaremnant. We carry out simulations of the collision between two 0.6M white dwarfsat various impact parameters and mass resolutions. For impact parameters less thanhalf the radius of the white dwarf, we nd such collisions produce ˇ 0.4 M of 56 Ni,making such events potential candidates for underluminous SNIa or a new class oftransients between Novae and SNIa.Key words: hydrodynamics { nuclear reactions, nucleosynthesis, abundances {(stars:) white dwarfs { (stars:) supernovae: general. 1 INTRODUCTIONType Ia supernovae (henceforth SNIa) play a key role inastrophysics as premier distance indicators for cosmology(Phillips 1993; Riess et al.1998; Perlmutter et al.1999), asdirect probes of low-mass star formation rates at cosmologi-cal distances (Scannapieco et al.2005; Mannucci et al.2006;Maoz 2008) and as signi cant contributors to iron-groupelements in the cosmos (Wheeler et al.1989; Timmes etal.1995; Feltzing et al.2001; Strigari 2006). Our current un-derstanding is that there are two major progenitor systemsfor these events. The rst possibility, the single-degeneratescenario, consists of a carbon-oxygen white dwarf in a bi-nary system evolving to the stage of central ignition by massoverow from a low-mass stellar companion (Whelan & Iben1973; Nomoto 1982; Hillebrandt & Niemeyer 2000). The sec-ond possibility, the double-degenerate scenario, consists ofthe merger of two white dwarfs in a binary system (Iben& Tutukov 1984; Webbink 1984; Yoon et al.2007). It is un-known at what relative frequency both of these channelsoperate (Livio 2000; Maoz 2008).Collisions between two white dwarfs, are likely to hap-pen less frequently than binary mergers. However, as dis-cussed in Timmes (2009) and Rosswog et al.(2009), theywill occur in globular clusters where the stellar densities areextremely high. For a typical globular cluster velocity dis-persion of ˇ5-10 km s