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.

如白矮星（WDS），星星大约是我们太阳弥撒的八倍。这些恒星已经完成了核的演化，将氢的核心转化为氦，然后转化为碳和氧气。然后，恒星会收缩，直到其电子的压力（量子机械电子退化压力）变得足够高，以使恒星在重力（想要收缩）和压力（想要扩大）之间达到平衡。该过程的终点是一颗恒星，大约是太阳的一半，大约是地球的半径。 WD这次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，并随时间缓慢而可以预测地冷却 - WDS是好时钟。这为实验室提供了无法在地球上复制的条件。温度约为1亿度，水的密度约为水的100万倍，并且要启动的精确时钟。有了这个几乎独特的实验室，可以进行异国情调的物理实验。 WD在大部分寿命中的冷却速度，WD通过光子的排放而冷却，但对于非常年轻且非常热的WD的情况，这会破裂。高于大约30,000k的表面温度高于冷却的主要来源是恒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。使用哈勃太空望远镜（HST）保护有史以来最大的热WDS样品，我们正在测试WD冷却模型，并推断地检查当前中微子理论是否正确。 WD在星形簇中产生的恒星簇WD中的扩散集中在簇芯中，它们是从最大的恒星演变而来的。在这个进化过程中，它们损失了大约一半的质量，质量太低而无法中心浓缩，因此开始缓慢地向外扩散。因为我们知道恒星的冷却时间的年龄，所以我们可以建立由于集群核心引力相互作用而引起的扩散常数 - 这是第一次完成。确定产生超新星的恒星质量。爆炸作为超新星的恒星的较低质量极限是对星系演化模型的关键输入。这些恒星产生特定的重元素，最终将其纳入后来的恒星和行星。我们通过在附近星系中寻找最发光的WD来开发了一种独特的方法来确定这一点。 WD周围的行星我们一直在寻找古代恒星群中WD周围的行星系统的证据。这里的积极成果可能会预示宇宙的早期生命。我们一直在使用HST（并将在2018年推出后使用其替代JWST）发现了古代恒星群中成千上万的热WD，并利用它们进行了许多这些实验。