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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=614540
• 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.

质量约为太阳八倍的恒星最终会以白矮星（WD）的形式结束生命。这些恒星已经完成了核演化，将氢核心转化为氦气，然后转化为碳和氧。然后恒星收缩，直到其电子压力（量子力学电子简并压力）变得足够高，使恒星能够在重力（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、半径约为地球半径的恒星。此时，WD 已经耗尽了其潜在的核燃料来源，因此它只是将其存储的热能辐射到太空中，并随着时间的推移缓慢且可预测地冷却 - WDS 是很好的时钟。这提供了一个物理实验室，其条件是地球上无法复制的；温度约为 1 亿度，密度为水的 100 万倍，并且有精确的时钟。有了这个几乎独一无二的实验室，就可以进行奇异的物理实验。 WD 的冷却速率 在 WD 的大部分生命周期中，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，这种情况就失效了。表面温度高于约 30,000K 时，主要的冷却来源是恒星核心产生的中微子。这些中微子能量非常低，很难在粒子加速器中产生和检测。我们使用哈勃太空望远镜 (HST) 来获取有史以来最大的热 WD 样本，并测试 WD 冷却模型并推断检验当前中微子理论是否正确。星团中 WD 的扩散 星团中产生的 WD 集中于星团核心，因为它们是从其最大质量的恒星演化而来的。在这个进化过程中，它们失去了大约一半的质量，质量变得太低而无法如此集中，因此开始缓慢向外扩散。因为我们从恒星的冷却时间得知了恒星的年龄，所以我们可以确定由于星团核心中的引力相互作用而产生的扩散常数——这是第一次实现这一点。确定产生超新星的恒星质量。作为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，最终融入后代的恒星和行星中。我们开发了一种独特的方法来确定这一点，即在附近星系的星团中寻找最明亮的白昼。 WD 周围的行星 我们一直在寻找古代星团中 WD 周围行星系统的证据。这里的积极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）在古代星团中发现数千个热 WD，并利用它们进行许多此类实验。