[论文解读] The largest structure of the Universe, defined by Gamma-Ray Bursts

I. Horváth, Jon Hakkila+1 more|arXiv (Cornell University)|Nov 5, 2013

Gamma-ray bursts and supernovae参考文献 15被引用 16

一句话总结

本文基于红移范围 1.6 < z < 2.1 内 31 个伽马射线暴（GRBs）的空间聚集，提出宇宙中迄今已知最大结构的存在——其尺寸超过 2000 Mpc。作者使用二维柯尔莫哥洛夫-斯米尔诺夫检验和二项概率，发现约 1/8 天空中 GRBs 的分布具有统计显著的集中，p 值为 0.0000055，表明该结构距离约十亿光年，规模达十亿光年，是斯隆长城的六倍大。

ABSTRACT

Research over the past three decades has revolutionized the field of cosmology while supporting the standard cosmological model. However, the cosmological principle of Universal homogeneity and isotropy has always been in question, since structures as large as the survey size have always been found as the survey size has increased. Until now, the largest known structure in our Universe is the Sloan Great Wall (SGW), which is more than 400 Mpc long and located approximately one billion light-years away. Here we report the discovery of a structure at least six times larger than the Sloan Great Wall that is suggested by the distribution of gamma-ray bursts (GRBs). Gamma-ray bursts are the most energetic explosions in the Universe. They are associated with the stellar endpoints of massive stars and are found in and near distant galaxies. Therefore, they are very good indicators of the dense part of the Universe containing normal matter. As of July 2012, 283 GRB redshifts have been measured. If one subdivides this GRB sample into nine radial parts and compares the sky distributions of these subsamples (each containing 31 GRBs), one can observe that the fourth subsample (1.6 &lt; z &lt; 2.1) differs significantly from the others in that many of the GRBs are concentrated in the same angular area of the sky. Using the two-dimensional Kolmogorov-Smirnov test, the significance of this observation is found to be less than 0.05 per cent. Fourteen out of the 31 Gamma-Ray Bursts in this redshift band are concentrated in approximately 1/8 of the sky. The binomial probability to find such a deviation is p=0.0000055. This huge structure lies ten times farther away than the Sloan Great Wall, at a distance of approximately ten billion light-years. The size of the structure defined by these GRBs is about 2000-3000 Mpc, or more than six times the size of the largest known object (SGW) in the Universe.

研究动机与目标

• 研究宇宙中超越斯隆长城（目前最大已知结构）的大尺度结构。
• 通过探测极端宇宙距离处的结构，检验宇宙学原理中普遍均匀与各向同性的假设。
• 确定伽马射线暴（GRBs）作为致密物质示踪器，能否揭示此前未被探测到的大尺度结构。
• 评估在红移分箱中 GRB 分布的空间聚集的统计显著性，以识别潜在的宇宙结构。

提出的方法

• 作者将 283 个测量的 GRB 红移值划分为九个径向红移分箱，每个分箱包含 31 个 GRBs，以分析宇宙时间中的角分布。
• 应用二维柯尔莫哥洛夫-斯米尔诺夫检验，将第四红移分箱（1.6 < z < 2.1）的天球分布与其他八个分箱进行比较。
• 计算二项概率，以评估在约 1/8 天空中，31 个 GRBs 中有 14 个聚集的偶然性概率。
• 分析聚焦于 GRBs 作为正常物质的示踪器，鉴于其与遥远星系中大质量恒星形成的相关性。
• 通过观察到的聚集所导出的 p 值评估统计显著性，p < 0.05% 的阈值表示显著偏离随机性。
• 结构尺寸通过红移范围与角扩展估算，得出尺度为 2000–3000 Mpc。

实验结果

研究问题

• RQ1 在特定红移范围内，伽马射线暴是否存在统计显著的大尺度聚集，表明存在一致的宇宙结构？
• RQ2 迄今已知宇宙最大结构的尺寸与斯隆长城相比如何？GRBs 能否揭示更大的结构？
• RQ3 观测到的 GRBs 在 1/8 天空区域的集中，其偶然发生的概率是多少？
• RQ4 在 z ≈ 1.8 处 GRBs 的空间分布是否挑战宇宙学原理中大尺度均匀性的假设？
• RQ5 GRBs 能否作为可靠示踪器，用于绘制遥远宇宙中重子物质的大尺度分布？

主要发现

• 第四红移分箱（1.6 < z < 2.1）包含 31 个 GRBs，其中 14 个集中在约 1/8 天空中，表明存在显著的空间聚集。
• 二维柯尔莫哥洛夫-斯米尔诺夫检验显示，观测到的非均匀性偏离具有小于 0.05% 的统计显著性。
• 此类聚集偶然发生的二项概率为 p = 0.0000055，表明具有极高的统计显著性。
• 由此产生的结构估计尺寸达 2000–3000 Mpc，使其规模超过斯隆长城六倍。
• 该结构距离约为十亿光年，远超斯隆长城的一亿光年。
• 该发现表明早期宇宙中存在一个一致且巨大的结构，挑战了大尺度均匀性的假设。