Massive stars die an explosive death as a core-collapse supernova (CCSN). The exact physical processes that cause the collapsing star to rebound into an explosion are not well understood^1,2,3, and the key to resolving this issue may lie in the measurement of the shape of CCSNe ejecta. Spectropolarimetry is the only way to perform this measurement for CCSNe outside the Milky Way and Magellanic Clouds. We present the infrared spectropolarimetric detection of a CCSN enabled by the new highly sensitive WIRC+Pol instrument at Palomar Observatory, which can observe CCSNe (magnitude M = −17 mag) out to 20 Mpc at ~0.1% polarimetric precision. Infrared spectropolarimetry is less affected than optical spectropolarimetry by dust scattering in the circumstellar and interstellar media, thereby providing a less biased probe of the intrinsic geometry of the supernova ejecta. SN 2018hna, a SN 1987A-like explosion, shows 2.0 ± 0.3% continuum polarization in the J band oriented at ~160° on sky 182 days after the explosion. Assuming a prolate geometry as in SN 1987A, we infer an ejecta axis ratio of <0.48 with the axis of symmetry pointing at a 70° position angle. The axis ratio is similar to that of SN 1987A, suggesting that the two CCSNe may share intrinsic geometry and inclination angles. Our data do not rule out oblate ejecta. We also observe one other CCSN and two thermonuclear supernovae in the J band. Supernova 2020oi, a stripped-envelope type Ic SN in Messier 100 has broadband p = 0.37 ± 0.09% at peak light, indicative of either a 10% asymmetry or host interstellar polarization. The type Ia SNe 2019ein and 2020ue have <0.33% and <1.08% polarization near peak light, indicative of asymmetries of less than 10% and 20%, respectively.

大质量恒星以核心坍缩超新星（CCSN）的形式爆炸死亡。导致坍缩恒星反弹到爆炸的确切物理过程尚不清楚^1,2,3，解决这个问题的关键可能在于测量 CCSNe 喷射物的形状。分光偏振法是对银河系和麦哲伦云以外的 CCSNe 进行这种测量的唯一方法。我们展示了帕洛玛天文台新的高灵敏度 WIRC+Pol 仪器对 CCSN 的红外光谱偏振检测，该仪器可以观察到 CCSNe（M级） = -17 mag) 到 20 Mpc，偏振精度约为 0.1%。与光学光谱偏振法相比，红外光谱偏振法受星周和星际介质中尘埃散射的影响较小，因此对超新星喷出物的内在几何形状的偏差较小。SN 2018hna 是一种类似 SN 1987A 的爆炸，在爆炸 182 天后，在天空中方向为 ~160° 的 J 波段显示出 2.0 ± 0.3% 的连续极化。假设 SN 1987A 中的长几何形状，我们推断喷射轴比 <0.48，对称轴指向 70° 位置角。轴比与 SN 1987A 相似，表明两个 CCSNe 可能共享固有几何形状和倾角。我们的数据不排除扁平喷射物。我们还在 J 波段观察到另外一颗 CCSN 和两颗热核超新星。超新星 2020oi，p  = 0.37 ± 0.09% 在峰值光处，表明 10% 的不对称性或宿主星际极化。Ia 型 SNe 2019ein 和 2020ue 在峰值光附近具有 <0.33% 和 <1.08% 的偏振，表明不对称性分别小于 10% 和 20%。