词条 超巨星
描述: 超巨星是体积最大、亮度最高的恒星。它们可能比太阳大几百倍，比太阳亮几千倍。它们占据赫兹普朗-拉塞尔图的顶部区域，绝对目视星等在-3 到-8 之间。超巨星的温度范围从大约3400开尔文（K）到超过20000开尔文（K）不等，它们要么是大质量恒星，要么处于恒星演化的后期阶段。超巨星可以根据它们的光谱来识别，超巨星可以通过它们的光谱来识别，其特征谱线对高亮度和低表面重力敏感：这些光谱线与较小恒星的线宽相比是较窄的。超巨星的典型例子包括猎户座的参宿四和造父变星。
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其他语言版本
- 阿拉伯语: نجم فائق الضخامة
- 德语: Überriesen
- 英语: Supergiant Star
- 西班牙语: Estrella supergigante
- 波斯语: ستاره ابرغول
- 法语: Étoile supergéante
- 意大利语: Stella supergigante
- 日语: 超巨星 (外部链接)
- 韩语: 초거성
- 巴西葡萄牙语: Estrela supergigante
- 繁体中文: 超巨星
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The red supergiant Betelgeuse
图注： The image shows Betelgeuse, a red supergiant in the constellation Orion, observed by the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA consists of many antennae spread across a plain in Northern Chile. The observations from all of these receivers is synthesised together by a central computer to form an image. The wide distances between the antennae mean that is can resolve very fine details.
Most stars we observe are just seen as points of light, but Betelgeuse is so large (with a radius about 1,400 times larger than the Sun) and is sufficiently nearby that it is one of the few stars to have been resolved to show it as an extended object.
Betelgeuse is a massive star, more than 14 times the mass of the Sun and is relatively young for a star (less than 14 million years old). However, its high mass led to it having a very hot core which burned through its hydrogen fuel quickly. It has since evolved through many stages and now appears as a red supergiant, it's final stage before exploding as a supernova. When such an explosion will happen is not known for certain, but it could be in around 100,000 years. Such an explosion would be visible from Earth, even during the day.
来源： ALMA (ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella
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赫罗图
图注： 这张图展示了不同恒星温度和亮度。每个点的大小代表恒星的半径，颜色代表人眼所看到的颜色。恒星的颜色从淡蓝色到淡橙红色不等，没有恒星具有像红、绿或蓝这样的纯颜色，因为恒星的光谱包含了许多不同颜色的光。然而，最红的恒星通常被称为红恒星，最蓝的恒星被称为蓝恒星。为了展示不同类型的恒星，制作这个图表的恒星样本选择上并没有反映出每种类型恒星的实际数量比例。
从左上到右下是一条长长的恒星带，这些恒星在其核心燃烧氢气，这被称为主序。在这条线上，我们可以看到参宿三（Mintaka）、波江座α星（Achernar）、天狼星A（Sirius A）、太阳和比邻星（Proxima Centauri）等恒星。在主序线右下方的比邻星周围的天体被称为红矮星。在红矮星的右下方是Teide 1和Kelu-1 A。这两个天体是褐矮星，它们的质量太低，核心没有足够的热量来持续地进行氢融合。由于它们不燃烧氢，褐矮星不被认为是主序星。"褐矮星"这个名字与它们的颜色无关。
在主序星的上方，我们发现次巨星、巨星和超巨星。这些是已经完成了核心的氢燃烧并演化成更大天体的恒星。恒星的亮度取决于其温度和大小，因此巨星比具有较小半径但相同温度的恒星更亮。随着时间的推移，这些天体将走向生命的尽头，经历行星状星云阶段或变成超新星。以行星状星云阶段结束生命的恒星会形成一种叫做白矮星的恒星残骸。这种天体比相同温度的恒星小得多，因此更暗淡，并且位于主序星带的显著下方。以超新星结束生命的恒星会成为黑洞或中子星。这些在这个图表上没有显示。
来源： IAU OAE/Niall Deacon
Stellar Evolution
图注： This diagram shows the life cycle of stars of different masses. The mass of the different types of star increases from bottom to top with time going from left to right.
The life cycle of a star depends on its mass, with lower mass stars have longer lifetimes. All stars form from clouds of gas that collapse under their own gravity. As the star collapses, its core becomes hotter and denser. If the star has a mass greater than 0.08 solar masses (0.08 times the mass of the Sun), the pressure of the star’s mass pushing down on its core creates a high enough core temperature for hydrogen fusion to ignite. This burns hydrogen into helium in the star’s core, providing a heat source to power the star and to stop its core from collapsing further. If the collapsing object has a mass below 0.08 solar masses then it does not ignite hydrogen fusion in its core. It continues to cool and slowly contract. Such substellar objects are known as brown dwarfs, shown here in the lowest row.
After stars have formed, they burn hydrogen in their cores and begin their so-called main sequence phase. The most massive stars (>25 solar masses, shown here at the top) have very high core temperatures and thus burn through their hydrogen fuel more quickly. This means they may only spend a few million years on the main sequence burning hydrogen in their cores. Once the hydrogen in the core is exhausted the star’s core contracts, becomes hotter and helium burning starts in the core. While the core contracts, the outer layers of the star expand and it becomes a supergiant. For the most massive stars strong stellar winds strip off the cooler outer layers, leading to the star being very large and very hot, a blue supergiant. Once helium is exhausted in the core, carbon is burned, and then heavier elements. Eventually the star ends with an iron core. Fusing iron into heavier elements does not generate energy so at this point fusion stops in the core. Once this core of iron is massive enough, it and the surrounding matter suddenly collapses to form a black hole and the outer layers are flung off in a supernova explosion.
Slightly lower mass stars (between 8 and 25 solar masses, seen here second top) evolve in a similar way although they do not have strong enough winds to push their outer layers away and become blue supergiants, instead it evolves into a red supergiant. While such stars also collapse and create supernova explosions. The remnant of the star’s core is not massive enough to collapse into a black hole. Instead, its electrons and protons combine to form neutrons and it is supported by a quantum mechanical effect called neutron degeneracy pressure. This results in the remnant of the star being a tiny neutron star, several solar masses in mass but only a few kilometres across.
For stars similar in mass to the Sun (between 0.4 and 8 solar masses, seen here in the middle row), the star burns hydrogen in its core until the hydrogen in its core is exhausted. At this point a hydrogen burning shell forms around the core. Eventually the core will become hot enough to burn helium into carbon and oxygen. After this the star is left with a carbon and oxygen core surrounded by shells burning helium and hydrogen. These shells are unstable producing thermal pulsations that convulse the star. Eventually these pulsations become so extreme that the star’s outer layers are thrown off. This leaves the carbon and oxygen core as a white dwarf supported by electron degeneracy pressure. The outer layers of the star form what is known as a planetary nebula (which doesn’t actually have anything to do with planets despite the name).
The lowest mass stars (seen here in the second bottom row) are so low in mass that their evolutionary timescales are much longer than the age of the universe. This means that none have evolved beyond the main-sequence. Low mass stars are fully convective meaning material in the core is constantly being mixed with material above. This means that all the hydrogen in the star would eventually be burned in the core, but this will take trillions of years.
来源： Danielle Futselaar/IAU OAE
