Relativistic jets from a Kerr black hole (BH) following the core collapse of a massive star (“collapsar”) is a leading model for gamma-ray bursts (GRBs). However, the two key ingredients for a Blandford–Znajek-powered jet—rapid rotation and a strong magnetic field—seem mutually exclusive. Strong fields in the progenitor star’s core transport angular momentum outward more quickly, slowing down the core before collapse. Through innovative multidisciplinary modeling, we first use MESA stellar evolution models followed to core collapse to explicitly show that the small length scale of the instabilities—likely responsible for angular momentum transport in the core (e.g., Tayler–Spruit)—results in a low net magnetic flux fed to the BH horizon, far too small to power GRB jets. Instead, we propose a novel scenario in which collapsar BHs acquire their magnetic “hair” from their progenitor proto–neutron star (PNS), which is likely highly magnetized from an internal dynamo. We evaluate the conditions for the BH accretion disk to pin the PNS magnetosphere to its horizon immediately after the collapse. Our results show that the PNS spin-down energy released before collapse matches the kinetic energy of Type Ic-BL supernovae, while the nascent BH’s spin and magnetic flux produce jets consistent with observed GRB characteristics. We map our MESA models to 3D general-relativistic magnetohydrodynamic simulations and confirm that accretion disks confine the strong magnetic flux initiated near a rotating BH, enabling the launch of successful GRB jets, whereas a slower-spinning BH or one without a disk fails to do so.

中文翻译：

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她有她妈妈的头发：通过 Stellar 到 Collapsar 模拟揭开黑洞磁场的起源


在大质量恒星的核心坍缩（“collapsar”）之后，来自克尔黑洞 （BH） 的相对论喷流是伽马射线暴 （GRB） 的主要模型。然而，布兰福德-兹纳耶克动力喷气式飞机的两个关键要素——快速旋转和强磁场——似乎是相互排斥的。祖星核心中的强磁场更快地向外传输角动量，在坍缩之前减慢核心的速度。通过创新的多学科建模，我们首先使用跟踪核心坍缩的 MESA 恒星演化模型来明确表明不稳定性的小长度尺度——可能是导致核心中角动量传输的原因（例如，泰勒-斯普雷特）——导致馈送到 BH 层的低净磁通量，太小而无法为 GRB 喷流提供动力。相反，我们提出了一种新的情景，其中坍缩 BH 从它们的祖先原中子星 （PNS） 那里获得磁性“头发”，PNS 可能是从内部发电机高度磁化的。我们评估了 BH 吸积盘在坍缩后立即将 PNS 磁层固定在其地平线上的条件。我们的结果表明，坍缩前释放的 PNS 自旋下降能量与 Ic-BL 型超新星的动能相匹配，而新生的 BH 的自旋和磁通量产生的射流与观察到的 GRB 特性一致。我们将 MESA 模型映射到 3D 广义相对论磁流体动力学模拟，并确认吸积盘限制了在旋转 BH 附近启动的强磁通量，从而能够成功发射 GRB 射流，而旋转速度较慢的 BH 或没有盘的 BH 则无法做到这一点。