The Dawn of Hydrogen Cosmology: First Stars, Dark Matter, and the Thermal History of the Early Universe

宇宙学的目标是了解从大爆炸到现在的宇宙历史。最初，宇宙充满了氢原子和氦原子的气体。最终，引力使恒星从这种气体中形成。天文学家已经看到了遥远的星系--恒星的集合--就像他们在宇宙不到5亿年时所看到的那样。但这些星系中的恒星可能并不是宇宙中形成的第一批恒星。确定宇宙中最早恒星的性质是很重要的。这些恒星第一次创造了碳、氮和氧等新元素。这改变了未来恒星的形成和演化方式。探测早期恒星发出的光是非常具有挑战性的。这项研究将转而分析无线电观测结果。来自早期宇宙的无线电信号可以间接记录第一批恒星的影响。通过研究这些信号，这项研究将帮助天文学家了解早期恒星在塑造现代宇宙中的作用。作为该项目的一部分，本科生、研究生和博士后水平的早期职业研究人员将接受培训。研究结果将在当地和地区性科学活动中与儿童和成年人分享。宇宙黎明期间第一批恒星、星系和黑洞的形成是观测宇宙学的下一个前沿。在这个时期，星系间介质(IGM)以中性氢气为主，通过它的红移21厘米线可以观察到它。早期IGM的热和电离历史编码了关于第一个发光物体性质的独特信息。一旦第一批恒星在z~30处形成，它们就会产生莱曼-阿尔法光子的背景，将中性氢自旋温度与IGM中的物理气体温度耦合起来。这导致在较暖的宇宙微波背景(CMB)下，21厘米线在吸收中变得可见。随后，长距离传播的X射线以热量的形式储存能量，并提高了IGM的温度。这种加热驱动平均21厘米的信号切换到CMB上方的发射，直到中性气体在再电离时期最终被电离，没有留下可检测到的信号。由于红移映射到21厘米线的频率，这些吸收和发射特征在IGM早期的演变将被印记在全天空射电频谱中。这项研究将使用EDGE双频段全天射电光谱仪的观测数据。EDGE的工作频率在50到200 MHz之间，红移30 z 6。这项研究的目标是限制早期宇宙中恒星形成、加热和电离的可信的天体物理模型参数。21CMFAST和其他模拟程序的理论模型将与观测结果相吻合。合作者将在他们的代码中加入额外的物理，以调查非标准物理对数据的任何贡献。该项目将为一名博士后研究和一名研究生的最后一年博士论文研究提供支持。它将为本科生提供从事天体物理学研究的机会，特别努力确保东道主机构所有感兴趣的学生都被鼓励追求这些机会，包括来自未被充分代表的人口和非传统背景的学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of cosmology is to understand the history of the Universe from the Big Bang through the present day. Initially, the universe was filled with a gas of hydrogen and helium atoms. Eventually gravity caused stars to form from this gas. Astronomers have seen distant galaxies--collections of stars--as they looked when the universe was less than 500 million years old. But the stars in these galaxies are probably not the first stars that formed in the universe. It is important to determine the properties of the earliest stars in the universe. These stars created new elements like carbon, nitrogen, and oxygen for the first time. This changed how future stars would form and evolve. Detecting light from early stars is very challenging. This research will instead analyze radio observations. Radio signals from the early universe can record the effects of the first stars indirectly. By studying these signals, this research will help astronomers understand the role of early stars in shaping the modern universe. Early-career researchers at the undergraduate, graduate, and postdoctoral levels will be trained as part of this project. Results from the research will be shared with children and adults at local and regional science events.The formation of the first stars, galaxies, and black holes during Cosmic Dawn is the next frontier in observational cosmology. During this epoch, the intergalactic medium (IGM) is dominated by neutral hydrogen gas, accessible to observations through its redshifted 21 cm line. The thermal and ionization history of the early IGM encodes unique information about the properties of the first luminous objects. Once the first stars form at z ~ 30, they produce a background of Lyman-alpha photons that couple the neutral hydrogen spin temperature to the physical gas temperature in the IGM. This causes the 21 cm line to become visible in absorption against the warmer cosmic microwave background (CMB). Later, X-rays traveling long distances deposit their energy as heat and raise the IGM temperature. This heating drives the average 21 cm signal to switch into emission above the CMB, until the neutral gas is eventually ionized during the epoch of reionization, leaving no detectable signal. The evolution of these absorption and emission features in the early IGM will be imprinted in the all-sky radio spectrum since redshift maps to frequency for the 21 cm line. This research will use observations from the EDGES dual-band all-sky radio spectrometer. EDGES operates in the frequency range between 50 and 200 MHz, spanning redshifts 30 z 6. The goal of the research is to constrain plausible astrophysical model parameters for star formation, heating, and ionization in the early Universe. Theoretical models from 21CMFAST and other simulation codes will be fit to the observations. Collaborators will incorporate additional physics into their codes to investigate any contributions from non-standard physics to the data. This project will provide support for one postdoctoral research and the final year of Ph.D. thesis research for one graduate student. It will provide opportunities for undergraduate students to engage in astrophysical research, with special efforts to make sure that all interested students at the host institution are encouraged to pursue these opportunities, including students from underrepresented populations and non-traditional backgrounds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.