近日，美国加州大学的Melodie M.Kao与美国国家射电天文台的Amy J.Mioduszewski等人合作，并取得一项新进展。经过不懈努力，他们通过分辨率成像证实了超冷矮星周围存在辐射带。相关研究成果已于2023年5月15日在国际权威学术期刊《自然》上发表。

该研究团队通过在8.4 GHz频率下进行高分辨率成像，证实了超冷矮星LSR J1835+3259的静态射电辐射在空间上具有可分辨性，并且呈现出与木星辐射带相似的双瓣对称结构。两个瓣之间相隔多达18个超冷矮星半径，在经过一年多的三次观测后仍然保持稳定存在。根据对受到LSR J1835+3259磁偶极约束的等离子体进行的分析，研究人员估计电子能量为15兆电子伏特，与木星的辐射带相一致。这些研究结果确认了最近关于恒星质量序列两端存在辐射带的预测，并且支持进一步重新评估旋转磁偶极在棕矮星、完全对流的M矮星和大质量恒星中产生非热静态射电辐射的作用。

研究人员表示，辐射带存在于所有大型太阳系行星的磁层中，包括地球、木星、土星、天王星和海王星。这些辐射带是持续存在的赤道区域，其中的相对论粒子能量可高达数十兆电子伏特，延伸范围可超过行星半径的10倍以上，并发出逐渐变化的射电辐射，对邻近卫星的表面化学产生影响。最近的观测表明，被称为超冷矮星的非常低质量恒星和棕矮星能够产生类似行星的射电辐射，例如周期性爆发的极光，这些极光源自于大规模的磁层电流。此外，这些超冷矮星还表现出缓慢变化的静态射电辐射，被假设为追踪低级别的日冕耀斑，尽管与经验性的多波长耀斑关系不完全一致。

附：英文原文

Title: Resolved imaging confirms a radiation belt around an ultracool dwarf

Author: Kao, Melodie M., Mioduszewski, Amy J., Villadsen, Jackie, Shkolnik, Evgenya L.

Issue&Volume: 2023-05-15

Abstract: Radiation belts are present in all large-scale Solar System planetary magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune¹. These persistent equatorial zones of relativistic particles up to tens of MeV in energy can extend farther than 10 times the planet’s radius, emit gradually varying radio emissions^2–4 and impact the surface chemistry of close-in moons⁵. Recent observations demonstrate that very low mass stars and brown dwarfs, collectively known as ultracool dwarfs, can produce planet-like radio emissions such as periodically bursting aurorae^6–8 from large-scale magnetospheric currents^9–11. They also exhibit slowly varying quiescent radio emissions^7,12,13 hypothesized to trace low-level coronal flaring^14,15 despite departing from empirical multi-wavelength flare relationships^8,15. Here we present high resolution imaging of the ultracool dwarf LSR J1835+3259 at 8.4 GHz demonstrating that its quiescent radio emission is spatially resolved and traces a double-lobed and axisymmetric structure similar in morphology to the Jovian radiation belts. Up to 18 ultracool dwarf radii separate the two lobes, which are stably present in three observations spanning more than one year. For plasma confined by the magnetic dipole of LSR J1835+3259, we estimate 15 MeV electron energies consistent with Jupiter’s radiation belts⁴. Our results confirm recent predictions of radiation belts at both ends of the stellar mass sequence^8,16–19 and support broader re-examination of rotating magnetic dipoles in producing non-thermal quiescent radio emissions from brown dwarfs⁷, fully convective M dwarfs²⁰, and massive stars^18,21.

DOI: 10.1038/s41586-023-06138-w

Source: https://www.nature.com/articles/s41586-023-06138-w