The nearby SN 1987A offers a unique opportunity to investigate the complex shock interaction between the ejecta and circumstellar medium. We track the evolution of the optical hot spots within the equatorial ring (ER) by analyzing 33 Hubble Space Telescope imaging observations between 1994 and 2022. By fitting the ER with an elliptical model, we determine its inclination to be 42.°85 ± 0.°50 with its major axis oriented −6.°24 ± 0.°31 from the west. We identify 26 distinct hot spots across the ER, with additional ones emerging over time, particularly on the western side. The hot spots initially show high velocities ranging from 390 to 1660 km s−1, followed by a deceleration phase around day ∼ 8000. Subsequent velocities vary from 40 to 660 km s−1. The light curves of the hot spots reach maxima between 7000 and 9000 days, suggesting a connection with the deceleration. Many spots are spatially resolved and show elongation perpendicular to the direction of motion, indicative of a short cooling time. To explain these results, we propose that each hot spot comprises dense substructures embedded in less dense gas. The initial velocities are then phase velocities, where the break occurs when the blast wave leaves the ER, while the late velocities reflect the propagation of radiative shocks in the dense substructures. We estimate that the dense substructures have a volumetric filling factor of and a total mass of .

中文翻译：

---

用哈勃太空望远镜追踪几十年来 SN 1987A 赤道环中激波的传播


附近的 SN 1987A 为研究喷射物和星周介质之间的复杂激波相互作用提供了独特的机会。我们通过分析 1994 年至 2022 年间的 33 次哈勃太空望远镜成像观测来追踪赤道环 （ER） 内光学热点的演变。通过用椭圆模型拟合 ER，我们确定其倾角为 42.°85 ± 0.°50，其长轴方向为西 −6.°24 ± 0.°31。我们在整个急诊室中确定了 26 个不同的热点，随着时间的推移，还会出现更多热点，尤其是在西部。热点最初表现出 390 到 1660 km s-1 的高速，然后在 ∼ 8000 天左右出现减速阶段。随后的速度从 40 到 660 km s-1 不等。热点的光曲线在 7000 到 9000 天之间达到最大值，表明与减速有关。许多点在空间上是分辨的，并显示出垂直于运动方向的伸长率，表明冷却时间短。为了解释这些结果，我们建议每个热点都包含嵌入密度较低的气体中的致密子结构。初始速度是相速度，当冲击波离开 ER 时发生断裂，而后期速度反映了辐射激波在致密子结构中的传播。我们估计，致密子结构的体积填充因子为 ，总质量为 。