导读
-- LOEB:CN --> 太阳的年龄约为46亿年。大约50亿年后，其核心的氢燃料将耗尽，太阳将开始膨胀成一颗红巨星。大约65亿年后，其核心的氦将点燃，太阳将进入持续约1亿年的氦燃烧阶段。
The Sun is ~4.6 billion years old. Within ~5 billion years, the hydrogen fuel in its core will run out, and the Sun will begin expanding into a red giant star. In ~6.5 billion years, the helium in its core will ignite and the Sun will settle into a helium-burning phase lasting ~100 million years. In ~7.5 billion years, the helium will be exhausted, and the Sun will enter the asymptotic giant branch, and its envelope will swell to near Earth’s orbit.
Most of the outer layers of the Sun will be shed off over a few hundred thousand years, so that in ~8 billion years the ejected gas will create an extended planetary nebula. The exposed hot core, a dense carbon-oxygen white dwarf, will carry about 0.55 solar masses. This massive remnant of the Sun will settle to a size comparable to that of the Earth.
As a result of this predictable evolution, the solar system will become a ghostly remnant of its former self once the age of the Universe will exceed 14.6 billion years. Its transformation will follow the following stages.
During the red giant phase, the Sun will engulf and completely incinerate the inner solar system. Mercury and Venus will be swallowed first. Earth will likely be engulfed as well, in which case the Moon will crash on Earth’s. surface as a result of drag on the puffed-up stellar envelope. The mass loss from the Sun will initially weaken the Sun’s gravity and push Earth out to about 1.7 times the current Earth-Sun separation, namely, 1.7 AU. But the bloated Sun will also drag Earth’s orbit inward, and the most detailed models find that Earth will be pulled in and be vaporized. Even if Earth narrowly escapes being swallowed, its oceans will boil, its atmosphere will be ripped away, and its surface will melt into a sea of lava, leaving behind a scorched, lifeless rock.
The white dwarf remnant will start with a surface temperature over 100,000 degrees Kelvin and gradually cool over time. With less gravitational pull from the dead Sun, the surviving planets: Mars, Jupiter, Saturn, Uranus, and Neptune, will drift outward. Their orbits will roughly double in size, shifting Jupiter to ~10 AU and Neptune to ~60 AU. The white dwarf’s luminosity will drop below a thousandth of the current solar luminosity within a few hundred million years. The subsurface oceans of Europa and Enceladus will eventually freeze solid. The Kuiper belt and Oort cloud will expand, and the loosely bound objects in the outer Oort cloud will be lost as interstellar objects. The changing gravity will also disrupt the asteroid belt, sending many space rocks towards interstellar space.
The white dwarf will contain no nuclear fuel and will only glow from leftover trapped heat. As it will cool down over trillions of years, the outer planets and their remaining moons will plunge into a deep freeze, with temperatures dropping down to tens of degrees above absolute zero.
Because of the chaotic shifts in gravity during the Sun’s death throes, millions of comets and asteroids from the Kuiper Belt and the Oort Cloud will fall inward toward the white dwarf. The immense gravitational tidal forces close to the dead Sun will shred these rocky objects into dust, forming a debris ring around the white dwarf that it will slowly consume over time.
Such debris disks are commonly found around old white dwarfs which represent the corpses of billions of ancient suns that died by now in the Milky-Way galaxy. The Sun was born and evolved in the last third of cosmic history. Most stars formed billions of years before the birth of the Sun.
The future solar system will lose its current inner planets, while the outer planets will survive on wider orbits around a cooling ember, and over trillions of years even that arrangement will slowly break apart.
Spectra of about a quarter to a half of white dwarfs show heavy elements in their atmospheres that gravity should have removed in days to centuries, so they must be continually fed by rocky debris. The surviving planets’ gravity, once the stabilizing mass of the star is reduced, scatters asteroids and comets onto orbits that pass close to the white dwarf, where they are shredded by tides into debris disks and accreted. Several white dwarfs show transiting fragments doing exactly this. The Solar System’s white dwarf will likely be polluted by rocky material the same way for billions of years, and its spectrum will carry the chemical signature of the asteroid belt.
With the Sun’s mass halved, the planets’ mutual perturbations are relatively stronger. Long-term simulations find the giant planets usually remain stable for tens of billions of years, but on timescales of trillions of years, passing stars and chaotic interactions will eventually eject planets one by one or send them into the star. Over such long timescales the white dwarf itself will cool dramatically and become a black dwarf, radiating almost nothing after 10 trillion years.
Interestingly, a white dwarf has a habitable zone, close in at a few hundredths of an AU, and it persists for billions of years as the star cools. No planet of the current Solar system will be there, since anything that close will be engulfed. But some white dwarfs have been found with planets that migrated inward or formed after the giant phase. If life could get a foothold on such a world, it would have a far longer stable habitable era than the Sun currently offers.
In this essay, I featured eight amazingly beautiful watercolors from a series created and sent to me by the celebrated artist, Greg Wyatt.
Professional website:
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https://avi-loeb.medium.com/https://www ... sorAviLoeb
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太阳的年龄约为46亿年。大约50亿年后，其核心的氢燃料将耗尽，太阳将开始膨胀成一颗红巨星。大约65亿年后，其核心的氦将点燃，太阳将进入持续约1亿年的氦燃烧阶段。大约75亿年后，氦将完全耗尽，太阳将进入渐近巨星阶段。h，其包层将膨胀到接近地球轨道。
太阳的大部分外层将在几十万年内脱落，大约80亿年后，喷射出的气体将形成一个广阔的行星状星云。裸露的炽热核心，一颗致密的碳氧白矮星，将携带约0.55个太阳质量。这颗巨大的太阳残骸最终会沉降到与……相当的大小。地球。
由于这种可预见的演化，一旦宇宙年龄超过146亿年，太阳系将变成昔日模样的幽灵般的残骸。它的转变将经历以下几个阶段。
在红巨星阶段，太阳将吞噬并彻底焚毁内太阳系。水星和金星将最先被吞噬。地球也可能被吞噬。如果太阳也膨胀，月球就会因为膨胀的恒星包层受到的阻力而撞击地球表面。太阳的质量损失最初会削弱太阳的引力，并将地球推向大约当前地日距离的1.7倍，即1.7天文单位。但膨胀的太阳也会将地球的轨道向内拉，最详细的模型表明，地球将被拉向一个……地球将被汽化。即使地球侥幸逃过被吞噬的命运，它的海洋也会沸腾，大气层会被撕裂，地表会融化成一片熔岩海，只留下一个焦黑死寂的岩石。
这颗白矮星残骸最初的表面温度将超过10万开尔文，并随着时间的推移逐渐冷却。由于来自死亡太阳的引力减弱，幸存的行星……火星、木星、土星、天王星和海王星将向外漂移。它们的轨道直径将大致翻倍，木星将移至约10天文单位，海王星将移至约60天文单位。白矮星的光度将在数亿年内降至当前太阳光度的千分之一以下。木卫二和土卫二的地下海洋最终将完全冻结。柯伊伯带和奥尔特云将膨胀。此外，外奥尔特云中那些松散束缚的天体将沦为星际天体。引力的变化也会扰乱小行星带，将许多太空岩石抛向星际空间。
这颗白矮星不含核燃料，只会因残留的热量而发光。随着它在数万亿年的时间里逐渐冷却，外行星及其剩余的卫星将会坠落。气温骤降至绝对零度以上几十度，进入极寒状态。
由于太阳垂死挣扎期间引力的剧烈变化，来自柯伊伯带和奥尔特云的数百万颗彗星和小行星将向白矮星内部坠落。垂死太阳附近巨大的引力潮汐力会将这些岩石天体撕成尘埃，形成碎片。围绕着白矮星的环状结构，它会随着时间的推移慢慢吞噬它。
这种碎片盘常见于年老的白矮星周围，这些白矮星是银河系中数十亿颗古老恒星的遗骸。太阳诞生于宇宙历史的最后三分之一时期，并在那里演化。大多数恒星的形成时间比太阳早数十亿年。
未来的太阳系将失去其核心内行星将逐渐消亡，而外行星将在围绕冷却的余烬的更宽阔的轨道上生存，经过数万亿年的时间，即使是这种结构也会慢慢瓦解。
大约四分之一到一半的白矮星的光谱显示，它们的大气层中含有重元素，这些重元素本应在几天到几个世纪内被引力清除，因此它们必须不断地从岩石碎片中获取养分。幸存行星的引力一旦恒星的稳定质量减少，它就会将小行星和彗星抛射到靠近白矮星的轨道上，在那里，它们会被潮汐力撕裂成碎片盘并被吸积。一些白矮星的凌日现象就证明了这一点。太阳系中的白矮星很可能在未来数十亿年里都会以同样的方式受到岩石物质的污染，其光谱也将随之发生变化。小行星带的化学特征。
太阳质量减半后，行星间的相互摄动相对增强。长期模拟发现，巨行星通常能稳定存在数百亿年，但在数万亿年的时间尺度上，恒星的掠过和混乱的相互作用最终会将行星逐一抛出或送入恒星内部。如此漫长的时间尺度下，行星的稳定性必然会发生显著变化。规模缩小后，白矮星本身会急剧冷却，变成黑矮星，10 万亿年后几乎不再辐射任何辐射。
有趣的是，白矮星拥有宜居带，其范围仅在几百分之一天文单位之内，并且随着恒星冷却，这个宜居带会持续数十亿年。目前太阳系中的任何行星都不会位于宜居带内，因为任何如此近的物体都会被吞噬。但有些白矮星却拥有宜居带。人们已经在一些行星上发现了向内迁移或在巨星阶段之后形成的行星。如果生命能够在这样的行星上立足，那么它所拥有的稳定宜居时期将比太阳目前所能提供的要长得多。
在这篇文章中，我介绍了著名艺术家格雷格·怀亚特创作并寄给我的一系列精美绝伦的水彩画中的八幅。
专业网站：
https://lweb.cfa.harvard.edu/~loeb/
https://avi-loeb.medium.com/https://www ... sorAviLoeb
https://open.spotify.com/show/1zhndXkvS ... rofAviLoeb
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原文链接：https://avi-loeb.medium.com/will-life-e ... 697e9df936
作者：Avi Loeb（哈佛大学天文系教授）
