Near and Far: White Dwarfs, Brown Dwarfs and a New Standard Candle

远近：白矮星、褐矮星和新标准蜡烛

• 批准号: RGPIN-2022-03051
• 负责人: Richer, Harvey
• 金额: $ 3.64万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=763075
• 关键词: Near; Far; White; Dwarfs; Brown

The research of the scientific program funded by this grant will take us from stars in the neighbourhood of the Sun to the furthest reaches of the universe. It will exploit the most sophisticated modern telescopes currently available to the world community, justifying Canada's contributions to these frontline facilities. It will expose HQP to a high impact international collaboration and provide a unique science experience that spans all of space and time.  The nearby region: (a) The fact that we can see stars means they are losing energy and hence evolving. For almost all stars, this energy is produced by nuclear reactions in the hot dense stellar core which consumes the star's hydrogen and produces heavier elements. At the end of this nuclear processing the star ejects all the material above its nuclear burning region, exposing the extremely dense and hot core which then slowly cools with time. The resulting stellar object is called a white dwarf (WD); typically half the mass of the Sun with a radius roughly that of the Earth. The most massive star capable of forming a WD is an extremely important quantity, all stars more massive than this limit explode as supernovae (SN) which control the chemical evolution and star formation rate in a galaxy. To determine this upper mass limit we have been exploring young star clusters that contain massive stars up to 10 or more times the mass of the Sun and establishing which of them produced WDs. It has been extremely challenging to locate WDs whose progenitor was more than 6 times the mass of the Sun, but some new ideas and techniques we have been developing is showing promise.   (b) We were successful in obtaining 20.5 hours of time on the soon-to-be-launched James Webb Space Telescope to search for (among other things) possible evidence of planetary systems around very old stars. The search will be in an ancient star cluster, imaging its WDs in the infrared (IR). About 5% of young WDs in the galaxy are known to be anomalously bright in the IR due to dust resulting from the destruction of planets or asteroids when the host star transitioned to a WD. Our search will be amongst the 12 billion year WDs in this ancient stellar system looking for evidence of planet formation in the very early universe. The distant region: The Hubble Constant, measuring the expansion rate of the universe, is one of the most fundamental cosmological parameters. Currently, the value from the standard cosmological model is in conflict with measurements in the local universe. Suggested causes range from systematic biases in one or both techniques to underestimated uncertainties in distance calibration, to the possibility of new physics in the early universe. To explore this conflict further we have developed a new distance technique using very luminous carbon-rich red giant stars. While still in its infancy, the method is proving to be extremely powerful and requires significantly less observing time than the standard techniques.

由这笔赠款资助的科学计划的研究将把我们从太阳附近的恒星带到宇宙的最远地方。它将利用国际社会目前可用的最先进的现代望远镜，证明加拿大对这些前线设施的贡献是合理的。它将让 HQP 参与具有高影响力的国际合作，并提供跨越所有空间和时间的独特科学体验。  附近区域：(a) 我们可以看到恒星这一事实意味着它们正在失去能量并因此不断演化。对于几乎所有恒星来说，这种能量都是由热致密恒星核心中的核反应产生的，该反应消耗恒星的氢并产生更重的元素。在核处理结束时，恒星喷射出其核燃烧区域上方的所有物质，暴露出极其致密和炽热的核心，然后随着时间的推移慢慢冷却。由此产生的恒星物体被称为白矮星（WD）；通常质量是太阳的一半，半径大约是地球的半径。能够形成WD的最大质量恒星是一个极其重要的数量，所有质量超过此极限的恒星都会爆炸为超新星（SN），超新星控制着星系中的化学演化和恒星形成速率。为了确定这个质量上限，我们一直在探索年轻的星团，这些星团包含质量高达太阳质量 10 倍或更多的恒星，并确定其中哪些产生了 WD。定位其前身质量超过太阳 6 倍的 WD 一直极具挑战性，但我们一直在开发的一些新想法和技术正在显示出希望。   (b) 我们成功地在即将发射的詹姆斯·韦伯太空望远镜上获得了 20.5 小时的时间来寻找（除其他外）非常古老恒星周围行星系统的可能证据。搜索将在一个古老的星团中进行，利用红外 (IR) 对其 WD 进行成像。已知银河系中大约 5% 的年轻 WD 在红外区域异常明亮，这是由于当主恒星转变为 WD 时行星或小行星的毁灭所产生的尘埃。我们的搜索将在这个古老恒星系统中进行 120 亿年的 WD，寻找极早期宇宙中行星形成的证据。遥远的区域：哈勃常数，测量宇宙的膨胀率，是最基本的宇宙学参数之一。目前，标准宇宙学模型的值与本地宇宙的测量结果相冲突。所提出的原因包括从一种或两种技术的系统偏差到距离校准的不确定性被低估，再到早期宇宙中出现新物理学的可能性。为了进一步探索这一冲突，我们利用非常明亮的富碳红巨星开发了一种新的距离技术。尽管该方法仍处于起步阶段，但已被证明非常强大，并且所需的观察时间比标准技术少得多。