Unlike today, the early Universe was filled mostly with neutral hydrogen, formed from protons and electrons that combined shortly after the Big Bang. Observations of distant quasars reveal that most of this hydrogen was reionized within the first billion years—a period known as the Epoch of Reionization. Yet, the sources and evolution of reionization remain uncertain. Recent observations from the James Webb Space Telescope (JWST) suggest that the massive stars in early, compact galaxies produced enough ionizing photons to complete reionization. However, it remains unclear how many of these photons actually escaped their host galaxies to ionize the intergalactic medium. Evidence indicates that stellar feedback—from both radiation and supernovae—is critical for clearing pathways that allow ionizing (LyC) photons to escape. For example, in cosmological simulations of galaxy formation, LyC escape peaks after supernova-driven winds clear galaxies of neutral gas and dust.   Because direct observations of LyC escape in the early Universe are impossible, astronomers turn to local analogs of the first galaxies to study these processes. Professor Renyue Cen and postdoctoral researcher Cody Carr have investigated the properties of galactic winds in nearby galaxies that emit ionizing radiation. In their paper “The Effect of Radiation and Supernova Feedback on LyC Escape in Local Star-forming Galaxies,” they proposed a new LyC escape sequence in which ionizing photons escape before the onset of supernovae—based on circumstantial evidence and radiation transfer modeling of spectral lines. Their predictions contrast with those of modern cosmological simulations.   In a follow-up paper submitted to Science, “Supernova-driven Winds Impede Lyman Continuum Escape from Dwarf Galaxies in the First 10 Myr,” Carr, Cen, and collaborators sought to isolate the time evolution of galactic winds and directly observe the LyC escape sequence. Using spectra from six local galaxies observed with the Hubble Space Telescope (HST), they traced the evolution of galactic winds alongside the LyC escape fraction (fesc), confirming their earlier predictions. Figure 1 shows these spectra: as fesc decreases with time, the absorption lines broaden (indicating higher velocities) and deepen (indicating higher densities), revealing an accelerating and increasingly massive wind. An artist’s rendering of the inferred LyC escape sequence is shown in Figure 2. LyC escape peaks early—before the onset of supernovae—when the starburst is younger than about 3 Myr. During this phase, radiation and stellar winds drive a relatively slow outflow. Between 3 and 5 Myr, the first supernovae explode, accelerating the wind and entraining more gas and dust. Although low-density may appear, fesc continues to decline on average. After roughly 5 Myr, the wind’s column density becomes sufficiently high to completely block LyC escape. These results suggest that cosmological simulations must incorporate more accurate treatments of radiation feedback to correctly capture how star-forming galaxies contribute to reionization.  

Figure 1: Spectra of six galaxies observed with the Hubble Space Telescope (HST).  Each color represents a new galaxy and time anti correlates with fesc.  Each column represents a different ion, probing the temperature range shown.  Magenta points represent the observed velocity of the wind measured at 90% the equivalent width, a measure of terminal wind speed.Figure 2: A new sequence for LyC escape proposed for compact, star forming galaxies.  

理解高红移超大质量黑洞（Supermassive Black Hole, SMBH）的形成是当前天体物理学中的核心科学问题之一。詹姆斯·韦布空间望远镜（JWST）的最新观测发现，大量红移 z>6 的明亮类星体，其中心黑洞质量已高达数十亿倍太阳质量，意味着这些黑洞在宇宙诞生不到十亿年时便已迅速成长。这一事实对现有的星系形成与黑洞增长模型提出了重大挑战。 近日，浙江大学天文学系吴子泳博士与岑人岳教授联合普林斯顿大学Romain Teyssier教授，利用高分辨率的宇宙学流体力学模拟，揭示了高红移典型晕环境中黑洞增长的全新图景。研究成果以题为《How Fast Could Supermassive Black Holes Grow At the Epoch of Reionization》的论文被国际著名天文学杂志ApJL接收（Wu, Cen & Teyssier 2025, arXiv:2510.16532）。 研究团队发现，早期宇宙中的超大质量黑洞成长经历了两个阶段：在第一阶段，黑洞在质量为 10^9-10^10 Msol 的典型暗物质晕中经历一个短暂的超爱丁顿吸积阶段，吸积速率可超过爱丁顿极限数倍，使其质量在短时间内迅速增长至 10^4-10^5 Msol。然而，这一高效吸积过程会激发强烈的活动星系核（AGN）反馈，加热并驱逐周围冷气体，导致吸积率迅速下降。 随后，黑洞进入第二阶段——自我调节的亚爱丁顿增长期。在此阶段，反馈能量持续抑制气体补给，使黑洞以低于爱丁顿极限的速率增长。令人意外的是，模拟显示，虽然超爱丁顿阶段可带来短期“跃升”，但强反馈会削弱后续气体供应，最终在红移 z∼10 时，持续爱丁顿极限吸积的黑洞反而比早期经历超爱丁顿增长的黑洞质量更大。 这一发现意味着：连续的爱丁顿吸积才是黑洞成长的最快可持续途径。若要解释红移 7–10 观测到的十亿倍太阳质量类星体，必须假设初始种子黑洞的质量已达10⁴–10⁵倍太阳质量，而非由恒星级黑洞经超爱丁顿吸积增长而成。 作者指出，这项研究不仅揭示了早期黑洞生长的自我调节机制，为理解早期宇宙中黑洞与宿主星系的协同演化提供了新的理论基础，也为未来的宇宙学模拟提供了关键约束。同时，如何产生质量高达10^5 Msol 的初始种子黑洞，将成为下一阶段研究的重要方向。 该研究得到了国家重点研发计划、国家自然科学基金、空间科学先导专项以及浙江大学科研基金的支持。相关模拟计算工作在浙江大学“SilkRiver”超级计算平台上完成。图一: 高分辨zoom-in 数值模拟在$z=10$ 时暗物质投影密度（下图）、气体投影密度（左上图）及气体温度（右上图）图。图二: 黑洞质量和吸积率随时间的演化，表明早期超大质量黑洞成长经历了两个阶段。图三: 模拟和观测中黑洞质量随红移的演化，表明连续的爱丁顿吸积才是黑洞成长的最快可持续途径。若要解释红移 7–10 观测到的十亿倍太阳质量类星体，必须假设初始种子黑洞的质量已达10⁴–10⁵倍太阳质量，而非由恒星级黑洞经超爱丁顿吸积增长而成。