本篇文章共分 7 段，說明恆星演化的最後階段與形成的最終結果：白矮星、中子星、與黑洞。並各自說明這幾種星體的成因與偵測方式。

本篇考題英文原文與對應之中文翻譯整理如下。練習作答解題時若有對語意不清楚之處，請仔細查閱對照，以提升閱讀理解能力。

Stellar Remnants 恆星殘骸

1. 恆星演化終點

   Eventually, all stars consume their nuclear fuel and collapse into one of three final states—white dwarf, neutron star, or black hole.

   最終，所有的恆星都會耗盡它們的核燃料，坍縮成三種最終狀態之一—白矮星、中子星或黑洞。

2. 白矮星的形成

   White dwarfs are extremely small stars with densities greater than any known terrestrial material. It is believed that white dwarfs began life as low-mass or medium-mass stars. As the star ages, it begins to collapse—become a dwarf—because it no longer produces sufficient radiant heat to counteract the contracting force of its gravity. Although some white dwarfs are no larger than Earth, the mass of such a dwarf can equal 1.4 times that of the Sun. A spoonful of such matter would weigh several tons. As a star contracts into a white dwarf, its surface becomes very hot and very bright. But, without a continuing source of energy, it will slowly become cooler and dimmer. Although none have been observed, the terminal stage of a white dwarf must be a small, cold, nonluminous body called a black dwarf.

   白矮星是極小的恆星，其密度大於任何已知的地球物質。人們認為，白矮星開始時是低質量或中等質量的恆星。隨著恆星的老化，它開始坍縮—成為一顆矮星—因為它不再產生足夠的輻射熱來抵消其重力的收縮力。儘管一些白矮星體積不比地球大，但這樣的矮星的質量可以相當於太陽的 1.4 倍。一勺這樣的物質會有幾噸重。當一顆恆星收縮成白矮星時，它的表面變得非常熱和非常亮。但是，如果沒有持續的能量來源，它將慢慢變得更冷，更暗淡。雖然沒有人觀察到，但白矮星的最終階段一定是一個小的、冷的、不發光的物體，稱為黑矮星。

3. 白矮星質量大小成因

   A study of white dwarfs produced what might at first appear to be a surprising conclusion: the smallest white dwarfs are the most massive, and the largest white dwarfs are the least massive. The explanation for this is that a more massive star has a greater gravitational force, and that greater gravitational force contracts the star into a smaller, more densely packed object than one gets with a less massive star. Thus, the smallest white dwarfs came from the collapse of stars that were larger and more massive than those the large white dwarfs came from.

   對白矮星的研究產生了一個乍看之下可能是令人驚訝的結論：最小的白矮星質量最大，而最大的白矮星質量最小。對此的解釋是，質量更大的恆星有更大的引力，而更大的引力將恆星收縮成比質量較小的恆星更小、更密集的物體。因此，最小的白矮星來自於那些比大白矮星更大、質量更高的恆星的坍縮。

4. 中子星的形成

   Extending this idea of larger stars collapsing to smaller stars leads to the prediction that very large stars would collapse to stars even smaller and more massive than white dwarfs. Named neutron stars, these objects are thought to be the remnants of supernova events (the collapse of a large, very massive star). If Earth were to collapse to the density of a neutron star, it would have a diameter equivalent to the length of a football field, and a pea-sized sample of this matter would weigh 100 million tons. This is approximately the density of an atomic nucleus; thus, neutron stars can be thought of as large atomic nuclei.

   將這種較大的恆星坍縮成較小的恆星的想法延伸開來，就可以預測非常大的恆星會坍縮成比白矮星更小、質量更大的恆星。這些物體被命名為中子星，被認為是「超新星事件」（一顆大質量恆星的坍縮）的殘留物。如果地球坍縮到中子星的密度，它的直徑將相當於一個足球場的長度，而這種物質的一個豌豆大小的樣本將重達 1 億噸。這大約是一個原子核的密度；因此，中子星可以被認為是大型原子核。

5. 偵測中子星的方式

   Although neutron stars have high surface temperatures, their small size would greatly limit their luminosity. Consequently, locating one visually would be extremely difficult. However, theory predicts that a neutron star would have a very strong magnetic field. Further, as a star collapses, it will rotate faster, for the same reason ice-skaters rotate faster as they pull in their arms. If the Sun were to collapse to the size of a neutron star, it would increase its rate of rotation from once every 25 days to nearly 1, 000 times per second. The radio waves generated by such rotating stars would be concentrated into two narrow beams, like the rotating light on a police car or ambulance. If Earth happened to be in the path of this beacon, the star would appear to blink on and off, or pulsate, as the radio waves swept past.

   雖然中子星有很高的表面溫度，但它們的體積小，會大大限制它們的發光度。因此，從視覺上找到一顆中子星將是非常困難的。然而，理論預測，中子星將有一個非常強大的磁場。此外，隨著一顆恆星的坍縮，它將旋轉得更快，就像溜冰者在收攏手臂時旋轉得更快一樣。如果太陽坍縮到中子星的大小，它的旋轉速度將從每 25 天一次增加到每秒近 1,000 次。這種旋轉的恆星產生的無線電波將被集中到兩個狹窄的光束中，就像警車或救護車上的旋轉燈。如果地球碰巧在這個信標的路徑上，當無線電波掃過時，這顆恆星會出現閃爍，或脈動。

6. 黑洞的成因

   In the early 1970s, a source that radiates short pulses of radio energy, called a pulsar (pulsating radio source), was discovered in the Crab Nebula. Visual inspection of this radio source revealed it to be a small star centered in the nebula. The first neutron star had been discovered. Are neutron stars made of the densest matter possible? No. During a supernova event, remnants of stars greater than three solar masses apparently collapse into objects even smaller and denser than neutron stars. Even though these objects would be very hot, their gravity would be so immense that even light could not escape the surface. Consequently, they would literally disappear from sight. These incredible bodies have appropriately been named “black holes.” Anything that moved too near a black hole would be swept in by its irresistible gravity and annihilated.

   在 1970 年代早期，在蟹狀星雲中發現了一個輻射短脈衝射電能量的來源，稱為脈衝星（脈衝射電源）。對這個射電源的目視檢查顯示它是一顆位於星雲中心的小星。第一顆中子星因此被發現了。中子星是由可能的最密集的物質構成的嗎？不是。在超新星事件中，大於三個太陽質量的恆星的殘餘物顯然會坍縮成比中子星更小、密度更大的物體。儘管這些物體會非常熱，但它們的引力是如此巨大，以至於連光都無法從其表面逃脫。因此，它們將真正地從人們的視線中消失。這些不可思議的物體被恰當地命名為「黑洞」。任何太靠近黑洞的東西都會被其不可抗拒的引力捲進去，並被湮滅。

7. 偵測黑洞的方式

   How can astronomers find an object whose gravitational field prevents the escape of all matter and energy? Theory predicts that as matter is pulled into a black hole, it should become very hot and emit a flood of x-rays before being engulfed. The first black hole x-ray sources were discovered in 1971 by detectors on satellites.

   天文學家如何才能找到一個其引力場阻止所有物質和能量逃逸的物體？理論預測，當物質被拉入黑洞時，它應該變得非常熱，並在被吞噬前發出大量的 X 射線。第一個黑洞 X 射線源是在 1971 年由衛星上的探測器發現的。