A new census of globular cluster pulsars

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。邓肯·洛里默和他的合作者将对银河系球状星团中的中子星数量进行详细的统计研究。球状星团提供的密集恒星环境充当了天体物理实验室，探测恒星演化以及双星和多星系统的动力学。球状星团中的中子星是星团中综合恒星形成历史的长期示踪，具有丰富的物理应用。射电脉冲星--快速旋转的高度磁化的中子星--为了解这一群体提供了一个非常强大的窗口。例如，对射电脉冲星的计时观测首次证明了球状星团中存在电离气体，并为大质量中子星的存在提供了最新证据，这些中子星挑战了许多超稠密物质的状态方程。预计未来球状星团的发现包括毫秒脉冲星和脉冲星-黑洞双星对。目前，已知的射电脉冲星有140颗，分布在26个球状星团中。这些发现中约有一半是在过去五年中由美国国家科学基金会资助的西弗吉尼亚州绿岸望远镜小组发现的。尽管取得了这些重大进展，但上一次对球状星团中的射电脉冲星数量的重大普查是在15年前进行的，当时在少数星团中已知的天体不到24个。当时，尚不清楚毫秒脉冲星(低质量X射线双星)的前体数量是否足以解释银河系球状星团中可能存在的10,000颗脉冲星的估计数量。洛里默博士计划对种群进行一项全面的新分析，以考虑双星运动、星际传播和无线电频率干扰造成的选择效应。他的团队在脉冲星观测和人口建模方面拥有广泛的经验，这是开发球状星团中射电脉冲星基本群体的详细蒙特卡罗模型所必需的。除了表征球状星团中射电脉冲星的整体大小和出生速率外，他们还将应用频率统计和贝叶斯统计分析来确定自旋周期、光度和(对于双星系统)轨道参数的潜在分布。他们还将讨论已知存在于球状星团中的较小的年轻脉冲星子集，以及那些由于引力辐射的发射而将在哈勃子星时间尺度上合并的双星。这些结果有望为以恒星演化模型为基础的中子星群体补充研究提供重要信息。他们还将帮助确定作为引力波来源的致密天体双星的可能数量。拟议中的研究将影响到其他一些领域，这些领域将使西弗吉尼亚州受益，教授天文学课程和一般的天文研究。具体地说，国际天文学联合会及其团队将：(A)为本科天文学专业学生开发一个免费提供的实验室部分；(B)为高中科学教师及其学生开发一个探究式学习工具；(C)提高西弗吉尼亚大学的国际研究知名度，并帮助增加科学、技术、工程和数学学科的学生人数；(D)加强未来国家和国际广播设施的科学案例；(E)提供一个开放源码的天文人口蒙特卡洛模拟工具库。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Dr. Duncan Lorimer and collaborators will undertake a detailed statistical study of the neutron star population in the globular clusters of the Milky Way Galaxy. The dense stellar environments provided by globular clusters act as astrophysical laboratories to probe stellar evolution and the dynamics of binary and multiple star systems. Neutron stars in globular clusters are long-lived tracers of the integrated star formation history in clusters and have a wealth of physical applications. Radio pulsars - rapidly spinning highly magnetized neutron stars - provide a very powerful window into this population. Timing observations of radio pulsars, for example, have demonstrated for the first time the existence of ionized gas in globular clusters and provide recent evidence for the existence of high-mass neutron stars which challenge many equations of state for super-dense matter. Future discoveries expected from globular clusters include binary pairs of millisecond pulsars and pulsar-black hole binary systems.Currently, 140 radio pulsars are known in 26 globular clusters. Around half of these discoveries have been made in the past five years by groups using the NSF-funded Green Bank Telescope in West Virginia. Despite these significant advances, the last major census of the radio pulsar population in globular clusters was carried out over 15 years ago when less than two-dozen objects were known in a handful of clusters. At that time, it was not clear whether the progenitor population of millisecond pulsars (the low-mass X-ray binaries) was sufficient to account for the estimated number of 10,000 pulsars suspected to exist in the Galactic globular cluster population. Dr. Lorimer plans a comprehensive new analysis of the population to take account of selection effects due to binary motion, interstellar propagation and radio frequency interference. His team has a broad range of experience in pulsar observations and population modeling necessary to develop detailed Monte Carlo models of the underlying population of radio pulsars in globular clusters.In addition to characterizing the overall size and birth-rate of radio pulsars in globular clusters, they will apply both frequentist and Bayesian statistical analyses to determine the underlying distributions of spin period, luminosity and (for binary systems) orbital parameters. They will also address the smaller subset of younger pulsars known to exist in globular clusters, and those binaries which will merge on sub-Hubble timescales due to the emission of gravitational radiation. These results are expected to provide vital input to complementary studies of the neutron star population which are based on models of stellar evolution. They will also help determine the likely size of the population of compact object binaries that contribute as gravitational-wave sources.The proposed research will impact upon a number of other areas which will benefit the state of West Virginia, teaching astronomy courses and astronomical research in general. Specifically, the PI and his team will (a) develop a freely-available laboratory component for undergraduate astronomy students; (b) develop an inquiry-based learning tool for high-school science teachers and their students; (c) raise the international research profile of West Virginia University and help to increase the number of students in Science, Technology, Engineering and Mathematics disciplines; (d) enhance the science case for future national and international radio facilities; (e) make available an open-source library of tools for Monte Carlo simulations of astronomical populations.