DELAYED NEUTRINO-DRIVEN SUPERNOVA EXPLOSIONS AIDED BY THE STANDING ACCRETION-SHOCK INSTABILITY
DELAYED NEUTRINO-DRIVEN SUPERNOVA EXPLOSIONS AIDED BY THE STANDING ACCRETION-SHOCK INSTABILITY
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DOI：
10.1088/0004-637x/694/1/664
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发表时间：
2007-08
期刊：
影响因子：
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通讯作者：
A. Marek;H. Janka
中科院分区：
文献类型：
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作者：
A. Marek;H. Janka
我们给出了恒星核坍塌的二维流体动力学模拟，并建立了详细分析中微子驱动的超新星爆炸的能量方面的框架。我们的结果证实，中微子加热机制仍然是一种可行的解释，可以解释质量范围更广的铁核超新星前驱物质的爆炸，但爆炸发生得更晚，发展方式与目前所认为的不同。中微子输运的计算采用基于“射线-射线+”近似的能量相关处理，其中中微子数、能量和动量方程用迭代求解模型Boltzmann方程得到的可变爱丁顿因子封闭。我们在这里关注15M☉前身的演化，并提供证据表明，激波复苏和爆炸是在中微子能量沉积的推动下，在核反弹后约600ms开始的。这比之前发现的11.2M☉恒星要晚得多，对于这颗恒星，我们也给出了Buras等人发表的爆炸模型的延续。在这两种情况下，爆炸的开始都是由站立的吸积激波不稳定性促成的。这种不稳定性表现出偶极和四极模的最高增长率，这导致了大幅度的双极激波振荡，并将激波推向更大的半径，从而增加了吸积物质在增益层中暴露于中微子加热的时间。激波后的对流翻转也得到加强，而激波停滞半径较小，则会被抑制或抑制。当爆炸开始时，激波显示出明显的全球形变，具有主要的偶极分量。在11.2M☉和15M☉爆炸中，持续时间较长的赤道下沉气流为增益层提供了新的气体，其中相当大一部分被中微子加热，导致抛射物的爆炸能量可能在数百毫秒内积聚。导致快速收缩、形成中子星的半径较小从而快速释放引力结合能的“软”核物态方程似乎更有利于爆炸的发展。自转具有相反的效果，因为从长远来看，它会导致中子星范围更广、温度更低，从而降低中微子的光度和平均能量，并总体上减少中微子的加热。中子星g模振荡，尽管我们看到了它们的存在，但声学机制在我们的模拟中并没有起到重要作用。虽然数值测试表明，我们的程序也能够很好地跟踪大幅度核心g模，如果它们是被激发的；在我们的超新星运行中，这种振荡的幅度仍然很小，而且由环形中子星注入的声能通量和中子星表面附近超音速下行气流的减速比中微子的能量沉积要小。
We present two-dimensional hydrodynamic simulations of stellar core collapse and develop the framework for a detailed analysis of the energetic aspects of neutrino-powered supernova explosions. Our results confirm that the neutrino-heating mechanism remains a viable explanation of the explosion of a wider mass range of supernova progenitors with iron cores, but the explosion sets in later and develops differently than thought so far. The calculations were performed with an energy-dependent treatment of the neutrino transport based on the “ray-by-ray plus” approximation, in which the neutrino number, energy, and momentum equations are closed with a variable Eddington factor obtained by iteratively solving a model Boltzmann equation. We focus here on the evolution of a 15 M☉ progenitor and provide evidence that shock revival and an explosion are initiated at about 600 ms after core bounce, powered by neutrino energy deposition. This is significantly later than previously found for an 11.2 M☉ star, for which we also present a continuation of the explosion model published by Buras et al. The onset of the blast is fostered in both cases by the standing accretion-shock instability. This instability exhibits highest growth rates for the dipole and quadrupole modes, which lead to large-amplitude bipolar shock oscillations and push the shock to larger radii, thus increasing the time accreted matter is exposed to neutrino heating in the gain layer. As a consequence, also convective overturn behind the shock is strengthened, which otherwise is suppressed or damped because of the small shock stagnation radius. When the explosion sets in, the shock reveals a pronounced global deformation with a dominant dipolar component. In both the 11.2 M☉ and 15 M☉ explosions long-lasting equatorial downflows supply the gain layer with fresh gas, of which a sizable fraction is heated by neutrinos and leads to the build-up of the explosion energy of the ejecta over possibly hundreds of milliseconds. A “soft” nuclear equation of state that causes a rapid contraction, and a smaller radius of the forming neutron star and thus a fast release of gravitational binding energy, seems to be more favorable for the development of an explosion. Rotation has the opposite effect because in the long run it leads to a more extended and cooler neutron star and thus lower neutrino luminosities and mean energies and overall less neutrino heating. Neutron star g-mode oscillations, although we see their presence, and the acoustic mechanism play no important role in our simulations. While numerical tests show that our code is also well able to follow large-amplitude core g-modes if they are instigated; the amplitude of such oscillations remains small in our supernova runs and the acoustic energy flux injected by the ringing neutron star and by the deceleration of supersonic downflows near the neutron star surface is small compared to the neutrino energy deposition.