As the largest virialized structures in the universe, galaxy clusters continue to grow and accrete matter from the cosmic web. Due to the low gas density in the outskirts of clusters, measurements are very challenging, requiring extremely sensitive telescopes across the entire electromagnetic spectrum. Observations using X-rays, the Sunyaev–Zeldovich effect, and weak lensing and galaxy distributions from the optical band, have over the last decade helped to unravel this exciting new frontier of cluster astrophysics, where the infall and virialization of matter takes place. Here, we review the current state of the art in our observational and theoretical understanding of cluster outskirts, and discuss future prospects for exploration using newly planned and proposed observatories.

中文翻译：

---

星系团外围的物理学

作为宇宙中最大的病毒化结构，星系团继续从宇宙网中生长和吸积物质。由于星团外围的气体密度低，测量非常具有挑战性，需要在整个电磁频谱范围内使用极其灵敏的望远镜。在过去的十年中，使用 X 射线、Sunyaev-Zeldovich 效应以及来自光学波段的弱透镜和星系分布的观测有助于解开星团天体物理学这一激动人心的新前沿，在那里发生物质的落入和病毒化。在这里，我们回顾了我们对集群外围的观察和理论理解的当前技术状态，并讨论了使用新规划和提议的天文台进行探索的未来前景。