天文學家發現擁有兩道行星碎屑環的白矮星

作者：威爾・鄧納姆By Will Dunham

華盛頓，11月7日（路透社）——數十億年後，太陽預料將耗盡燃料，並大幅膨脹成所謂紅巨星，最後拋出外層，留下緻密核心，也就是白矮星。我們太陽系中的部分行星將被摧毀，其他行星則可能存活下來。WASHINGTON, Nov 7 (Reuters) - Billions of years from now, the sun is expected to run out of fuel and greatly expand into what is called a red giant, eventually shedding its outer layers and leaving behind its dense core, a white dwarf. Some of the planets in our solar system would be destroyed while others might survive.

研究人員如今發現一顆白矮星，周圍有行星碎屑以不尋常的構造環繞旋轉，或許能讓人一窺我們太陽系在遙遠未來可能出現的一種結局。Researchers have now spotted a white dwarf with planetary debris swirling around it in an unusual configuration that may offer a peek into one possible outcome for our solar system in the distant future.

不同於先前觀測到的類似系統，環繞這顆白矮星的碎屑盤似乎由兩個明顯不同的環組成。研究人員表示，這個碎屑盤可能是由兩個嵌在環中的行星體或較小岩質天體塑造成形；這些天體在恆星劇烈的死亡掙扎中倖存下來。Unlike in similar systems previously observed, the debris disc surrounding this white dwarf appears to consist of two distinct rings. The researchers said the disc may have been shaped by two planetary or smaller rocky bodies that are embedded in the rings after managing to survive the star's violent death throes.

這顆名為J1328−1450的白矮星位於銀河系，距離地球約1600光年，所在位置在室女座。1光年是光在一年中行進的距離，也就是5.9兆英里（9.5兆公里）。這些觀測是使用歐洲南方天文台位於智利的甚大望遠鏡完成。The white dwarf, named J1328−1450, is located in the Milky Way roughly 1,600 light-years from Earth, in the constellation Virgo. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). The observations were made using the European Southern Observatory's Chile-based Very Large Telescope.

在這項發現之前，天文學家已確認21顆周圍有碎屑的白矮星；這些白矮星全都只有單一碎屑盤，而不是新觀測所揭示的雙重物質環。Prior to this discovery, astronomers had identified 21 white dwarfs with debris surrounding them, all of which had a single disc and not a double ring of material as the new observations reveal.

智利費德里科聖瑪麗亞技術大學（Universidad Técnica Federico Santa María）天文學家費利佩・拉戈斯-比爾切斯（Felipe Lagos-Vilches）說：「這顯示行星系統的殘餘物可能具有比我們先前想像更複雜的結構，也進一步支持一項觀點：行星的岩質天體可能在恆星轉變為白矮星的過程中存活下來。」他是這項發表於《自然天文學》（Nature Astronomy）期刊研究的作者之一。"It shows that the remnants of a planetary system can have a much more complex structure than we previously thought, and provides further support to the idea that planetary rocky bodies may survive the transformation of a star into a white dwarf," said astronomer Felipe Lagos-Vilches of Universidad Técnica Federico Santa María in Chile, one of the authors of the study published in the journal Nature Astronomy.

這顆白矮星的質量約為太陽的47%，卻被壓縮在直徑約與地球相同的大小之中。The white dwarf has a mass about 47% that of the sun, jam-packed into a diameter roughly the same as that of Earth.

存活下來的行星體可能是較大型、並遭到嚴重破壞的行星殘餘。其中一個可能約有矮行星冥王星的大小，另一個則比它更小。The surviving planetary bodies may be remnants of larger and heavily disrupted planets. One of them may be around the size of the dwarf planet Pluto, with the other one smaller than that.

拉戈斯-比爾切斯表示，原本那顆恆星在劇烈膨脹成紅巨星之前，可能曾擁有一個行星系統；它吞噬了一些最靠近內側的行星，而軌道較遠的行星則存活下來。Lagos-Vilches said the original star may have hosted a planetary system before it expanded dramatically into a red giant, engulfing some of the innermost planets while ones with more distant orbits survived.

拉戈斯-比爾切斯說：「這個行星系統並未完全消失。一些倖存的岩質天體可能受到重力擾動，被帶入高度橢圓的軌道，使它們接近這顆白矮星。」"The planetary system did not completely disappear. Some surviving rocky bodies may have been gravitationally perturbed onto highly eccentric orbits that brought them close to the white dwarf," Lagos-Vilches said.

拉戈斯-比爾切斯說：「距離足夠近的天體，會被白矮星的重力撕裂。它們的物質散布成含有塵埃與氣體的碎屑盤。不過，兩個相對較大的岩質天體可能在這些碎屑中存活下來。」"Objects that came sufficiently close were disrupted by the white dwarf's gravitational force. Their material was spread into a debris disc containing dust and gas. However, two relatively large rocky bodies may have survived within this debris," Lagos-Vilches said.

拉戈斯-比爾切斯表示，這兩個天體的存在，或許有助於解釋周圍物質為何分布成一對同心氣體環。The presence of the two bodies may help explain the distribution of the surrounding material into a pair of concentric gaseous rings, Lagos-Vilches said.

拉戈斯-比爾切斯說：「外環的鎂含量相較於內環大幅偏低。這暗示它們可能源自不同的母體天體，也可能來自某個岩質天體的不同層；該天體因白矮星強大的重力場而過度接近，進而被撕裂。」"The outer ring is strongly depleted in magnesium compared with the inner ring. This suggests that they may originate from different parent bodies, or possibly from different layers of a rocky body that was disrupted when it went too close to the white dwarf due to its strong gravitational field," Lagos-Vilches said.

一窺未來A GLIMPSE OF THE FUTURE

拉戈斯-比爾切斯表示，大約50億年後，太陽將成為紅巨星。In about 5 billion years, the sun will become a red giant, Lagos-Vilches said.

拉戈斯-比爾切斯說：「太陽最終會失去外層，變成白矮星。內太陽系將受到劇烈影響。水星和金星預料會被膨脹中的太陽吞噬；至於地球是否也會在這個階段被吞噬，目前仍沒有明確共識。外側行星的命運則不同。木星、土星以及更遙遠的天體，應該有大得多的存活機會。」"It will eventually lose its outer layers and become a white dwarf. The inner solar system will be dramatically affected. Mercury and Venus are expected to be engulfed by the expanding sun, while there is still no clear consensus on whether Earth will also be engulfed during this phase. The fate of the outer planets is different. Jupiter, Saturn and the more distant bodies should have a much better chance of surviving," Lagos-Vilches said.

在太陽變成白矮星後，存活下來的行星殘餘、衛星和小行星，可能被拉近到足以遭重力撕裂的距離。After the sun becomes a white dwarf, surviving planetary remnants, moons and asteroids could potentially be drawn close enough to the white dwarf to be torn apart by gravitational forces.

拉戈斯-比爾切斯說：「因此，像J1328−1450周圍這樣的碎屑盤，可能代表我們自身行星系統在極其遙遠未來的一個可能階段。」"A debris disc like the one around J1328−1450 could therefore represent one possible stage in the very distant future of our own planetary system," Lagos-Vilches said.

（華盛頓威爾・鄧納姆報導；丹尼爾・沃利斯編輯）(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)