Glossary term: 白矮星
Description: 達到八倍太陽質量的恆星預計會以白矮星的形式結束其生命。這其中就包括我們的太陽。白矮星的密度非常高，一顆典型白矮星的質量與太陽相當，但被擠壓成了一個僅比地球略大的球。白矮星不再通過其內核的核反應產生能量，但會因為剩餘的能量而發光。溫度較高的白矮星會呈現出藍色或白色，這是因為它們的表面溫度非常高，會輻射出能量。白矮星的內核可能由氦、碳-氧或氧-氖-鎂組成，具體取決於恆星的初始質量。白矮星並不會在其自引力作用下收縮，這是由於其內部存在電子簡並壓——一種量子現象——帶來的阻力。電子簡並壓最大只能支持 1.4 倍太陽質量的白矮星。質量大於這個極限（稱為錢德拉塞卡極限）的恆星殘骸要麼是中子星，要麼是黑洞。
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
This is an automated transliteration of the simplified Chinese translation of this term
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In Other Languages
- 阿拉伯語: الأقزام البيضاء
- 孟加拉語: সাদা বামন
- 德語: Weißer Zwerg
- 英語: White Dwarf
- 西班牙語: Enana blanca
- 法語: Naine blanche
- 義大利語: Nana Bianca
- 日語: 白色矮星 (external link)
- 巴西葡萄牙語: Anã Branca
- 簡體中文: 白矮星
Related Media
Sirius A with his faint white dwarf companion Sirius B
Caption: This Hubble Space Telescope image highlights Sirius, the brightest star in Earth’s night sky, appearing as an intensely luminous object at the center with prominent cross-shaped diffraction spikes. These spikes, along with the saturated glow around the main star, are caused by the Sirius' light being spread out by the telescope and camera used to make this image. Slightly below and to the left of the main star, a tiny point of light marks Sirius B, a much dimmer object captured thanks to Hubble’s high sensitivity.
Sirius A is an A-type star, known for its high surface temperature and strong white-blue light, while Sirius B is a compact white dwarf, the dense remnant of a star that has exhausted its nuclear fuel. Together, they form a well-known Binary star system located about 8.6 light-years from Earth.
Sirius B was originally a higher mass and brighter star that burned through its hydrogen fuel more quickly than Sirius A. This led to Sirius B evolving into a red giant and eventually ending its life as a planetary nebula, leaving only the remains of its core as a white dwarf orbiting Sirius A.
Credit: NASA, ESA, H. Bond (STScI), and M. Barstow (University of Leicester)
credit link
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Related Diagrams
赫羅圖
Caption: 這張圖展示了不同恆星溫度和亮度。每個點的大小代表恆星的半徑，顏色代表人眼所看到的顏色。恆星的顏色從淡藍色到淡橙紅色不等，沒有恆星具有像紅、綠或藍這樣的純顏色，因為恆星的光譜包含了許多不同顏色的光。然而，最紅的恆星通常被稱為紅恆星，最藍的恆星被稱為藍恆星。為了展示不同類型的恆星，製作這個圖表的恆星樣本選擇上並沒有反映出每種類型恆星的實際數量比例。
從左上到右下是一條長長的恆星帶，這些恆星在其核心燃燒氫氣，這被稱為主序。在這條線上，我們可以看到參宿三（Mintaka）、波江座α星（Achernar）、天狼星A（Sirius A）、太陽和比鄰星（Proxima Centauri）等恆星。在主序線右下方的比鄰星週圍的天體被稱為紅矮星。在紅矮星的右下方是Teide 1和Kelu-1 A。這兩個天體是褐矮星，它們的質量太低，核心沒有足夠的熱量來持續地進行氫融合。由於它們不燃燒氫，褐矮星不被認為是主序星。"褐矮星"這個名字與它們的顏色無關。
在主序星的上方，我們發現次巨星、巨星和超巨星。這些是已經完成了核心的氫燃燒並演化成更大天體的恆星。恆星的亮度取決於其溫度和大小，因此巨星比具有較小半徑但相同溫度的恆星更亮。隨著時間的推移，這些天體將走向生命的盡頭，經歷行星狀星雲階段或變成超新星。以行星狀星雲階段結束生命的恆星會形成一種叫做白矮星的恆星殘骸。這種天體比相同溫度的恆星小得多，因此更暗淡，並且位於主序星帶的顯著下方。以超新星結束生命的恆星會成為黑洞或中子星。這些在這個圖表上沒有顯示。
Credit: IAU OAE/Niall Deacon
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Stellar Evolution
Caption: 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.
Credit: Danielle Futselaar/IAU OAE
License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons
