Doing Physics in the Cores of Globular Star Clusters

在球状星团的核心进行物理学研究

• 批准号: RGPIN-2016-03665
• 负责人: Richer, Harvey
• 金额: $ 5.39万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=708596
• 关键词: Doing; Physics; Cores; Globular; Star

Stars up to about eight times the mass of our Sun end their lives as white dwarf stars (WDs). These stars have completed their nuclear evolution, converting their core of hydrogen into helium and then into carbon and oxygen. The star then contracts until the pressure of its electrons (the quantum mechanical electron degeneracy pressure) becomes high enough for the star to reach a balance between gravity (that wants to contract it) and pressure (that wants to expand it). The end point of this process is a star about half the mass of the Sun and about the radius of the Earth. The WD has depleted its potential source of nuclear fuel by this time, so it simply radiates its stored thermal energy out into space and cools slowly and predictably with time - WDS are good clocks. This provides a physical laboratory with conditions that cannot be reproduced on Earth; temperature about 100 million degrees, density of order of 1 million times that of water and a precise clock to boot. With this almost unique laboratory, it is possible to carry out exotic physical experiments. The rate of cooling of WDs Over most of its life, a WD cools by the emission of photons, but this breaks down for the case of very young and very hot WDs. Above surface temperatures of about 30,000K the dominant source of cooling is the production of neutrinos in the core of the star. These neutrinos are of very low energy and hard to produce and detect in particle accelerators. Using the Hubble Space Telescope (HST) to secure the largest samples of hot WDs ever obtained, we are testing WD cooling models and inferentially examining whether current neutrino theory is correct. Diffusion of WDs in star clusters WDs produced in star clusters are concentrated towards the cluster core as they evolve from its most massive stars. During this evolutionary process, they lose about half their mass, become too low in mass to be so centrally concentrated and thus begin to diffuse slowly outwards. Because we know the age of the star from its cooling time, we can establish the diffusion constant due to gravitational interactions in the cluster core - the first time that this has been accomplished. Determination of the masses of stars that produce supernovae. The lower mass limit of stars that explode as supernovae is a critical input into galaxy evolution models. These stars produce specific heavy elements that are eventually incorporated into later generations of stars and planets. We have developed a unique way of determining this by searching for the most luminous WDs in clusters in a nearby galaxy. Planets around WDs We have been searching for evidence of planetary systems around WDs in ancient star clusters. A positive result here could potentially herald an early rise to life in the universe. We have been using the HST (and will use its replacement JWST after its launch in 2018) discovering thousands of hot WDs in ancient star clusters and exploiting them to carry out a number of these experiments.

质量大约是太阳八倍的恒星以白色矮星（WD）的形式结束了它们的生命。这些恒星已经完成了它们的核演化，将它们的氢核心转化为氦，然后转化为碳和氧。然后，星星收缩，直到它的电子压力（量子力学电子简并压力）变得足够高，使星星在引力（想要收缩它）和压力（想要膨胀它）之间达到平衡。这个过程的终点是一颗质量约为太阳一半、半径约为地球的星星。WD此时已经耗尽了其潜在的核燃料来源，因此它只是将其储存的热能辐射到太空中，并随着时间的推移缓慢冷却- WDS是很好的时钟。这提供了一个物理实验室，其条件在地球上无法复制;温度约为1亿度，密度为水的100万倍，精确的时钟靴子。有了这个几乎独一无二的实验室，就有可能进行奇异的物理实验。WD的冷却速率在其生命的大部分时间里，WD通过发射光子来冷却，但对于非常年轻和非常热的WD来说，这是不可能的。当表面温度超过30,000 K时，冷却的主要来源是星星核心的中微子产生。这些中微子的能量非常低，很难在粒子加速器中产生和检测。利用哈勃太空望远镜（HST）获得有史以来最大的热WD样本，我们正在测试WD冷却模型，并立即检查当前中微子理论是否正确。星星团中WD的扩散星星团中产生的WD在它们从最大质量的恒星演化时向团核集中。在这个进化过程中，它们失去了大约一半的质量，质量变得太低，无法集中在中心，因此开始慢慢向外扩散。因为我们从星星的冷却时间中知道了它的年龄，我们可以确定由于星系团核心的引力相互作用而产生的扩散常数--这是第一次完成。产生超新星的恒星质量的测定。超新星爆炸的恒星的质量下限是星系演化模型的关键输入。这些恒星产生特定的重元素，这些元素最终被纳入后代的恒星和行星中。我们已经开发了一种独特的方法来确定这一点，通过寻找附近星系中最明亮的WD。WDs周围的行星我们一直在寻找古老的星星星团中WDs周围行星系统的证据。一个积极的结果可能预示着宇宙中生命的早期崛起。我们一直在使用HST（并将在2018年发射后使用其替代品JWST），在古老的星星集群中发现数千个热WD，并利用它们进行一些这样的实验。