WD-WD head-on collisions的发生率可能与SNe Ia发生率一样高
The rate of WD-WD head-on collisions may be as high as the SNe Ia rate
摘要：
研究表明，当半长轴a=1-300 AU的白矮星-白矮星（WD-WD）双星被一个近心r_{p, out} \sim 3-10 x a的恒星质量外摄动所环绕时，在~5 Gyr内有百分之几的机会发生迎头碰撞。这样一个扰动器足够远，可以让三重系统在数百万个轨道上保持完整，同时有效地与WD-WD双星交换角动量。在约5%的初始取向中，内轨道有效地扫描零角动量区域中的（等能量）相空间。在这些系统中，随着运行轨道数（N）的增加，双星系统的近心点逐渐接近r_p ~ a/2N。在N~10^5（a/30 AU）轨道内，可能发生碰撞。这是通过执行\simten千三体积分，并解释了简单的分析参数。碰撞被保守地限制为“干净”碰撞，其中碰撞前的所有通道都大于4R_WD=4x10^9cm。特别地，在最后一个单轨道内，近心从r_p>4R_WD变为r_p<2R_WD的碰撞值。在这些情况下，潮汐变形和广义相对论（GR）修正的影响可以忽略不计。WD以>3000 km/s的高速相互接近，碰撞可能引爆WD，导致Ia型SNe。如果WD的显著部分驻留在这样的三元组中，则这样的冲突的速率与Ia型SNe速率一样高，并且有可能一些或所有Ia型SNe以这种方式发生。这样的SNe有一个独特的引力波特征，这将允许在未来进行决定性的识别。
英文摘要：
We show that a White Dwarf-White Dwarf (WD-WD) binary with semi-major axis a=1-300 AU, which is orbited by a stellar mass outer perturber with a moderate pericenter r_{p, out} \sim 3-10 x a, has a few percent chance of experiencing a head-on collision within ~5 Gyr. Such a perturber is sufficiently distant to allow the triple system to remain intact for millions of orbits while efficiently exchanging angular momentum with the WD-WD binary. In ~ 5% of the initial orientations, the inner orbit efficiently scans the (equal energy) phase space in the region of zero angular momentum. In these systems, the binary experiences increasingly closer, stochastic, pericenter approaches r_p ~ a/2N with the increasing number (N) of orbits elapsed. Within N~10^5(a/30AU) orbits, a collision is likely to occur. This is shown by performing \simten thousand 3-body integrations and is explained by simple analytic arguments. The collisions are conservatively restricted to "clean" collisions in which all passages prior to the collision are greater than 4R_WD=4x10^9cm. In particular, within the last single orbit, the pericenter changes from r_p>4R_WD to a collision value of r_p<2R_WD. The effects of tidal deformations and General Relativistic (GR) corrections are negligible in these scenarios. The WDs approach each other with a high velocity >3000 km/s and the collision is likely to detonate the WDs leading to a type Ia SNe. If a significant fraction of WDs reside in such triples, the rate of such collisions is as high as the SNe Ia rate, and it is possible that some or all type Ia SNe occur in this way. Such SNe have a unique gravitational wave signature, which will allow a decisive identification in the future.
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