词条 M 型星
描述: 光谱类型为 "M" 的恒星。天文学家通过光谱中是否存在分子吸收带（主要来自钛氧化物）来识别 M 型星。它们的典型（有效）温度大约在 2500 K 到 3700 K 之间。与其他恒星相比，它们在人眼中呈现红色。光谱类型为 M 的主序星被称为红矮星。M型星也可以是红巨星或红超巨星；这些类型的恒星大多是 M 型星，但也包括一些 K 型星以及一些具有强烈的碳光谱特征的更奇特的恒星类型。猎户座的参宿四就是一颗 M 型超巨星。
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词条和定义状态： 该术语的英文原始定义已通过天文研究人员和教师的审核 该术语及其定义的译文仍待审核
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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其他语言版本
- 阿拉伯语: نجمة من النوع M
- 德语: M-Stern
- 英语: M-type Star
- 法语: Étoile de type M
- 意大利语: Stella di tipo M
- 日语: M型星 (外部链接)
- 韩语: M형 별
- 繁体中文: M 型星
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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
来源链接
相关图表
一颗 M 型恒星的光谱
图注： M 型恒星 2MASS J15581272+8457104 的光谱。波长在 400 纳米到 700 纳米之间的光谱线的颜色大致与人眼看到的该波长光线的颜色一致。波长低于 400 纳米和高于 700 纳米时，人眼几乎看不到光，这两条线分别被染成蓝色和红色。
黑线显示的是恒星大气中不同元素的原子、离子和分子造成的光谱吸收线。这些原子、离子和分子会吸收特定波长的光线，从而在光谱中形成尖锐的暗线。这些线条的强度取决于恒星大气层的温度。如果两颗恒星的大气层温度不同，那么由相同元素混合而成的两颗恒星的光谱中可能会出现截然不同的光谱线。M 型恒星的大气层足够冷，可以形成一些化合物。这些化合物通常在天文学中被称为分子，尽管它们在化学中并不是严格意义上的分子。这些分子会在 M 型恒星的光谱中产生如此之多的谱线，以至于这些谱线看起来会合并成巨大的条带，从而从光谱中去除一大块。在 M 型恒星中，氧化钛在可见光中有大量这样的波段，占据了光谱的大部分区域。
来源： IAU OAE/SDSS/Niall Deacon
