华盛顿 10月16日电：天文学家首次识别出一颗绿色恒星，记录下了一种名为白矮星的致密恒星残骸。这颗白矮星在吞食了曾环绕其运行的行星的岩石残骸后，变成了一种幽灵般的黄绿色。
WASHINGTON, Oct 16 : Astronomers for the first time have identified a green star, documenting a dense stellar remnant called a white dwarf that became a ghostly shade of chartreuse after ingesting rocky debris from planets that once had orbited it.
恒星的颜色通常由其温度决定，较冷的恒星呈橙色，太阳及与其类似的恒星呈白色，而温度最高的恒星则呈淡蓝色。
A star's color typically is governed by its temperature, with cooler stars appearing orange, the sun and stars similar to it appearing white, and the hottest ones appearing a pale blue.
但白矮星的规律则有所不同。白矮星是低质量至中等质量恒星耗尽核燃料并抛弃外层后留下的核心。大多数白矮星的颜色与其他恒星相似，平均颜色为白色。但随着时间的推移，其化学成分的变化会使其中一些呈现出更罕见的颜色。
But the formula is different for a white dwarf, which is the leftover core of a low- to medium-mass star that burned through its nuclear fuel and blew off its outer layers. Most white dwarfs have colors similar to other stars, and their average color is white. But changes in their chemistry over time can turn some of them into rarer colors.
这颗新发现的绿色恒星被命名为WD J1330+6435，是银河系中的一颗白矮星，距离地球约280光年，位于天龙座。一光年是光在一年中行进的距离，即5.9万亿英里（9.5万亿公里）。
The newly identified green one, named WD J1330+6435, is a white dwarf in the Milky Way galaxy that is located about 280 light-years from Earth in the constellation Draco. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
发表在《RAS技术与仪器》（RAS Techniques and Instruments）杂志上的这项研究的第一作者、英国华威大学的天体物理学家马克·霍兰兹（Mark Hollands）表示：“我们最初对这颗白矮星产生兴趣，是因为行星物质的碎片落在了其表面，使其外层富含了钙、锂，尤其是钠等元素。”
"We first became interested in this white dwarf because bits of planetary material have fallen onto its surface, enriching its outer layers in elements including calcium, lithium and, in particular, sodium," said astrophysicist Mark Hollands of the University of Warwick in England, lead author of the study published in the journal RAS Techniques and Instruments.
在正常恒星中，钠会吸收一个非常特定波长的橙色——正是这种橙色赋予了钠路灯独特的颜色。
In normal stars, sodium absorbs a very specific wavelength of orange — the same orange that gives sodium street lamps their characteristic color.
霍兰兹说：“然而，在这颗特定的白矮星中，密度极高，以至于钠原子不断受到周围氦原子的轰击，从而改变了钠原子的能级。”
"In this particular white dwarf, however, the density is so high that the sodium atoms are constantly being bombarded by surrounding helium atoms, which alters the sodium atomic energy levels," Hollands said.
霍兰兹说：“最终的结果是，钠原子不再吸收一个非常狭窄波长的橙色——它们吸收黄色、橙色以及部分红色波长。由此留下的是一颗散发着美丽的黄绿色光芒的恒星，这对于类太阳恒星来说是不可能的。”
"The end result is that the sodium atoms no longer absorb one very narrow wavelength of orange — they absorb the yellows, oranges and some of the red wavelengths. And what you're left with is a star that has a beautiful chartreuse green glow, something that wouldn't be possible for sun-like stars," Hollands said.
这一发现是一个旨在评估人眼所见的白矮星颜色的项目的一部分。白矮星通常具有相当于太阳一半的质量，但其体积却被压缩到地球的大小。
The discovery was part of a project assessing the color of white dwarfs as human eyes would see them. A white dwarf typically has half the mass of the sun compacted into the size of Earth.
华威大学天体物理学家兼研究合著者鲍里斯·甘西克（Boris Gänsicke）表示：“因为白矮星是超级致密的恒星——它们的大致大小与地球相当，但包含约相当于地球16.5万倍的质量——所以即使是少量的钠也能阻挡来自恒星的大量橙色光。”
"Because white dwarfs are super-dense stars — they are roughly the size of the Earth, but contain about 165,000 times its mass — even a small amount of sodium blocks out a large amount of the orange light coming out of the star," University of Warwick astrophysicist and study co-author Boris Gänsicke said.
甘西克说：“归根结底，这一切都非常类似于画家调色板上的颜色调配。他们从几种基本颜色开始，然后将它们混合在一起，形成画画所需的任何颜色。去掉混合中的一部分颜色，输出的颜色就会改变。”
"In the end, it's all very similar to the mixing of colors in the palette of a painter. They start with a few basic colors, then mix them together to form any color they need for their painting. Take away some of the color going into the mix, and the output will change," Gänsicke said.
一颗呈三文鱼粉色的恒星 研究人员研究了位于距离地球约65光年以内的151颗白矮星，其中白色为其平均颜色。
A STAR THAT IS SALMON PINK The researchers studied 151 white dwarfs located within about 65 light-years of Earth, with white the average color.
- 一个白矮星呈现出已知恒星中最红的色调之一，即三文鱼粉色。它被命名为WD J1011+2845，距离地球48光年，位于小狮座。这一次，改变调色板的不是钠，而是碳。
One showed perhaps the reddest hue of any known star, a salmon pink. Named WD J1011+2845, it is located 48 light-years from Earth in the constellation Leo Minor. This time, it was not sodium that was changing the palette, but carbon.
甘西克说：“在这种情况下，不是有什么东西撞击了恒星，而是碳从其深层内部涌出。”
"Rather than something hitting the star, in this case the carbon comes out from its deep interior," Gänsicke said.
研究人员使用的数据包括利用新墨西哥州的一架望远镜通过斯隆数字巡天项目（Sloan Digital Sky Survey）获得的恒星光谱观测结果，以及他们开发的白矮星光谱模型。
Data used by the researchers included light spectrum observations from the Sloan Digital Sky Survey using a telescope in New Mexico, as well as white dwarf spectrum models they developed.
他们发现，白矮星的颜色根据大气成分分为不同的组。富碳的白矮星通常呈粉色或紫色。那些富含行星系统碎裂残骸的白矮星则倾向于黄色。具有混合氢氦大气的较低温度白矮星则倾向于青色或淡蓝色色调。总的来说，它们的颜色几乎涵盖了光谱的每一个颜色。
They found that white dwarf colors divide into distinct groups based on atmospheric composition. Carbon-rich white dwarfs usually were pink or purple. Those enriched with debris from shattered remnants of planetary systems leaned toward yellow. Lower-temperature white dwarfs with mixed hydrogen and helium atmospheres tended toward a cyan or pale blue hue. In all, they spanned almost every color of the spectrum.
虽然WD J1330+6435是现实世界中记录的首个绿色恒星实例，但绿色恒星在科幻小说中一直存在，包括在最近的漫画书电影《女超人》（Supergirl）中。霍兰兹说：“这确实表明，宇宙有时和科幻小说能构想出的任何东西一样离奇。”
While WD J1330+6435 was the first documented example of a green star in the real world, green stars have existed in science fiction, including in the recent comic book movie "Supergirl." "It does show that the universe is sometimes just as weird as anything science fiction can conjure up," Hollands said.