Stellar-wind feedback and magnetic fields around young compact star clusters: 3D magnetohydrodynamics simulations

<p>
3D MHD datasets from
<a href="https://doi.org/10.1051/0004-6361/202554057">
https://doi.org/10.1051/0004-6361/202554057
</a>.
The datasets contain the final time-step (390 kyr) for clusters I, I (high B),
I (low B), and III (see Tab. 1 in the publication).
The data was generated with the open-source MHD code PLUTO
(<a href="https://plutocode.ph.unito.it/">
https://plutocode.ph.unito.it/
</a>)
and is in the <code>dbl.h5</code> format.
For the format specification and visualisation options, see
<a href="https://plutocode.ph.unito.it/userguide.pdf">
https://plutocode.ph.unito.it/userguide.pdf
</a>,
Ch. 12.
PyPLUTO is recommended for data processing, see <a href="https://pypluto.readthedocs.io/en/stable/">
https://pypluto.readthedocs.io/en/stable/
</a>.
</p>

<p><strong>Abstract of the related publication:</strong></p>

<p>
<strong>Context.</strong>
The environments of young star clusters are shaped by the interactions of the
powerful winds of massive stars and their feedback on the cluster birth cloud.
Several young star clusters show diffuse γ-ray emission on the degree scale,
which hints at ongoing particle acceleration.
</p>

<p>
<strong>Aims.</strong>
To date, particle acceleration and transport in star-cluster environments are
not well understood. A characterisation of magnetic fields and flow structures
is necessary to progress towards physical models. Previous work has largely
focused on 100 pc scale feedback or detailed modelling of wind interaction of
just a few stars. We aim to bridge this gap. We focus in particular on compact
clusters in order to study collective effects arising from stellar-wind
interaction. Objects in this class include Westerlund 1 and R136.
</p>

<p>
<strong>Methods.</strong>
We performed 3D ideal-magnetohydrodynamics simulations of compact young massive
star clusters. We kinetically injected stellar winds for 46 individual very
massive stars (M > 40 M⊙) distributed in a spherical region of radius ≤ 1 pc.
We included a sub-population of five magnetic stars with increased dipole field
strengths of 0.1–1 kG, and we studied the evolving superbubble over several
hundred thousand years.
</p>

<p>
<strong>Results.</strong>
The bulk flow and magnetic fields show an intricate non-uniform morphology that
is critically impacted by the relative position of individual stars. The
cluster wind terminates in a strong shock that is non-spherical, and similar to
the flow, it has non-uniform properties. The magnetic field is composed of both
highly tangled sections and coherent quasi-radial field-line bundles. Steep
particle spectra in the teraelectronvolt domain arise naturally from the
variation of magnetic field magnitude over the cluster-wind termination shock.
This finding is consistent with γ-ray observations. We deem the scenario of
petaelectronvolt particle acceleration as unlikely.
</p>

本数据集为来自文献<https://doi.org/10.1051/0004-6361/202554057>的三维磁流体动力学（Magnetohydrodynamics, MHD）数据集。数据集包含星团I、高磁场版本I（high B）、低磁场版本I（low B）以及星团III的最终时间步数据（390 kyr，即39万年），详细信息参见论文表1。该数据由开源MHD代码PLUTO（https://plutocode.ph.unito.it/）生成，存储格式为`dbl.h5`。关于格式规范与可视化选项，可参考PLUTO用户指南（https://plutocode.ph.unito.it/userguide.pdf）第12章。数据处理推荐使用PyPLUTO工具，详见其官方文档：https://pypluto.readthedocs.io/en/stable/。

### 相关研究论文摘要
#### 研究背景
年轻星团的环境由大质量恒星的强风相互作用及其对星团诞生云的反馈效应共同塑造。目前已有多个年轻星团被观测到存在角尺度上的弥散γ射线辐射，这暗示着星团内正发生持续的粒子加速过程。

#### 研究目标
迄今为止，星团环境中的粒子加速与输运机制尚未得到充分阐释。若要构建完备的物理模型，需先对星团内的磁场结构与流场特征进行系统性表征。既往相关研究多聚焦于100秒差距（parsec, pc）尺度的星际反馈，或是仅针对少量恒星的风相互作用开展精细化建模。本研究旨在填补这一研究空白，我们重点关注致密年轻大质量星团，以探究恒星风相互作用所产生的集体效应，此类天体的典型代表包括Westerlund 1与R136。

#### 研究方法
我们针对致密年轻大质量星团开展了三维理想磁流体动力学模拟。将46颗质量大于40倍太阳质量（solar mass, M⊙）的特大质量恒星的恒星风以动力学方式注入，这些恒星分布在半径≤1 pc的球形区域内。我们引入了一个包含5颗磁星的亚群，这些磁星的偶极磁场强度为0.1~1千高斯（kiloGauss, kG），并对数十万年间演化的超级泡（superbubble）结构进行了追踪分析。

#### 研究结果
整体流场与磁场均呈现出复杂的非均匀形态，其结构特征显著受限于单个恒星的相对空间位置。星团风终止于非球形的强激波结构，其物理特性与整体流场类似，同样表现出非均匀性。磁场结构兼具高度缠结的区域与连贯的准径向磁力线束。太电子伏特（teraelectronvolt, TeV）能段的陡粒子能谱，可自然由星团风终止激波处的磁场强度变化产生，这一结果与γ射线观测数据相符。我们认为拍电子伏特（petaelectronvolt, PeV）能段的粒子加速场景可能性较低。