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Astronomers witness star devouring a planet: Possible preview of the ultimate fate of Earth
By studying countless stars at various stages of their evolution, astronomers have been able to piece together an understanding of the life cycle of stars and how they interact with their surrounding planetary systems as they age. This research confirms that when a sun-like star nears the end of its life, it expands anywhere from 100 to 1,000 times its original size, eventually engulfing the system's inner planets. Such events are estimated to occur only a few times each year across the entire Milky Way. Though past observations have confirmed the aftermath of planetary engulfments, astronomers have never caught one in the act, until now.
With the power of the Gemini South Adaptive Optics Imager (GSAOI) on Gemini South, one half of the International Gemini Observatory, operated by NSF's NOIRLab, astronomers have observed the first direct evidence of a dying star expanding to engulf one of its planets. Evidence for this event was found in a telltale "long and low-energy" outburst from a star in the Milky Way about 13,000 light-years from Earth. This event, the devouring of a planet by an engorged star, likely presages the ultimate fate of Mercury, Venus, and Earth when our sun begins its death throes in about five billion years.
"These observations provide a new perspective on finding and studying the billions of stars in our Milky Way that have already consumed their planets," says Ryan Lau, NOIRLab astronomer and co-author on this study, which is published in the journal Nature.
For most of its life, a sun-like star fuses hydrogen into helium in its hot, dense core, which allows the star to push back against the crushing weight of its outer layers. When hydrogen in the core runs out, the star begins fusing helium into carbon, and hydrogen fusion migrates to the star's outer layers, causing them to expand, and changing the sun-like star into a red giant.
Such a transformation, however, is bad news for any inner-system planets. When the star's surface eventually expands to engulf one of its planets, their interaction would trigger a spectacular outburst of energy and material. This process would also put the brakes on the planet's orbital velocity, causing it to plunge into the star.
The first hints of this event were uncovered by optical images from the Zwicky Transient Facility. Archival infrared coverage from NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which is able to peer into dusty environments in search of outbursts and other transient events, then confirmed the engulfment event, named ZTF SLRN-2020. "Our team's custom reanalysis of all-sky infrared maps from NEOWISE exemplifies the vast discovery potential of archival survey data sets," said NOIRLab astronomer Aaron Meisner, another co-author on the paper.
注释：
engulf: v
表示"吞没；席卷；吞噬"，means "flow over or cover completely"，如：The waves engulfed the boat.大浪吞没了小舟。
engulfment: n
表示"吞没；席卷；吞噬"， engulf的名词形式。
telltale：n; adj
1. n表示" 告密者；迹象；"，means "someone who gossips indiscreetly"，如：The teacher did not notice that I was cheating until that rotten telltale told her.在那个该死的告密者告诉老师之前，老师并没有注意到我作弊。
2. adj表示"无法掩饰的"，means "disclosing unintentionally"，如：I could see from the telltale look in her eyes that she loved him. 我从她那无法掩饰的眼神里可以看出她爱他。
engorge: v
表示"狼吞虎咽；使充血"，means "overeat or eat immodestly; make a pig of oneself"，如：So the fox fasted for three days, and got very slim so it could came into the garden and engorged. 于是它一狠心绝食三日，减肥之后，终于钻进葡萄园内饱餐一顿。His eyes were engorged with blood.他双目充血。
presage: n
表示"预示；预言"，means "indicate by signs"，如：Suddenly he had a presage about the near danger. 他突然对即将到来的危险有了一种预感。
throe: n
表示" 剧痛；阵痛"，means "severe spasm of pain"，如：Transport is taught by throe. 剧痛孕育了狂喜。
fuse: n
表示" 保险丝;导火线"，means "short piece of wire that melts and breaks the circuit if the current exceeds a safe level"，如：Changing a fuse is one of those fiddly jobs I hate.我最不愿意干换保险丝这类活儿了。
helium: n
表示"氦"，如：Helium and neon are inert gases. 氦和氖为惰性气体。
plunge: v
表示" 投入；跳入"，means " an act of plunging, especially head first into water"，如：I waved my dog to plunge into the water. 我挥手示意我的狗跳入水中
exemplify: v
表示" 例证；示范"，means " be a typical example of sth"，如：I will exemplify my point with a story.我会用一个故事举例说明我的观点。
中文简要说明：
预习一下地球最终的命运，通过研究各种演化阶段的无数恒星，天文学家们已经能够拼凑出对于恒星的生命周期以及它们晚期的变化。当类似太阳的恒星接近它的生命终点时，它的大小会膨胀100到1000倍，最终吞噬行星系统的内部行星。这样的事件在整个银河系中每年仅发生几次。尽管过去的观察已经确认了行星吞噬事件的结果，但天文学家从未在行动中捕捉到过，如今已经发表在国际知名期刊上。经测量，被吞噬的行星质量约为木星的1-10倍左右，
据综合科学物理网站phys.org以及双子星天文台报导，由美国国家光学红外线天文研究实验室（NOIRLab）运营的国际双子星（Gemini South）南方天文台的天文学家们观察到了第一个直接证据，显示一颗垂死的恒星正在膨胀并且吞噬它的一颗行星。这次事件发生在距离地球约13000光年的银河中一颗「长而低能量」爆发的恒星上。这种事件，即一颗膨胀的恒星吞噬行星，预示着水星、金星和地球等行星在50亿年后，当太阳迈向死亡阶段时的最终命运。
天文学家在智利使用双子座南方天文台观察到第一个令人信服的证据，表明一颗垂死的类太阳恒星正在吞噬一颗行星。（International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani）
这项发表在《自然》期刊上的研究的共同作者，NOIRLab的天文学家雷恩（Ryan Lau）表示：「这些观测为寻找和研究已经消耗了行星的我们的银河系中数十亿颗恒星提供了一个新的视角。」大多数时候，类似太阳的恒星在大部分的生命周期中，将氢融合成氦，并将能量释放在炙热而密集的核心中，这使得恒星能够抵抗外层的重力。当核心中的氢耗尽时，恒星开始将氦融合成碳，并且氢融合移居到恒星的外层，导致外层膨胀，并将类似太阳的恒星变成红巨星（Red Giant）。
然而，这样的变化对于内部系统的行星而言并不是好消息。当恒星的表面最终膨胀以吞噬其中的一颗行星时，它们的相互作用会引发壮观的能量和物质爆发。这个过程也会减缓行星的轨道速度，导致它坠入恒星。
这起称作为ZTF SLRN-2020的大事件，也获得了美国NASA确认了了这次的吞噬事件。双子座南方天文台提供了必要数据，当天文学家们将该天文台的自适应光学图像与NASA的NEOWISE的红外图像结合起来时，才证实了天文学家们的猜想，并首次鉴定了行星吞噬事件。研究的主要作者基沙雷德（Kishalay De）说：「这证明了我们作为行星几乎可以确定的未来的命运。」
从吞噬中爆发的特征，以及所排放物质的组成，让天文学家们了解了恒星的质量和其所吞噬行星的质量。从分析中，团队估计该原始恒星的质量约为太阳的0.8-1.5倍，而被吞噬的行星质量则为木星质量的1-10倍。经过约100天的吞噬事件，以及行星被吞噬的方式等。
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