经济学人双语版-大爆炸的时刻到了? Time for a Big Bang?

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FlyTitle: Stellar evolution

Betelgeuse, one of the brightest stars in the sky, has been behaving strangely

参宿四是天空中最亮的恒星之一,近来它表现异常

经济学人双语版-大爆炸的时刻到了? Time for a Big Bang?

THE GREAT Collapsing Hrung Disaster of the Year 03758 is shrouded in mystery. All that is known about this event, mentioned in a footnote to “The Hitchhiker’s Guide to the Galaxy”, by Douglas Adams, is that the only survivor was the father of one of the story’s main characters, Ford Prefect—and that it took place on one of the planets orbiting Betelgeuse.

银河系系年03758年的那场异物大坍塌灾难充满了神秘色彩。道格拉斯·亚当斯(Douglas Adams)在《银河系漫游指南》的脚注中提到,关于这一事件,我们只知道唯一的幸存者是故事的主角之一福特·普里弗克特(Ford Prefect)的父亲,以及事件发生在环绕参宿四运行的一颗行星上。

Betelgeuse is a red supergiant star in Orion, a prominent constellation that spans the celestial equator. It is one of the brightest objects in the night sky, easily visible to the naked eye. It has around ten times the mass of the sun, and if it were at the centre of the solar system its outer edge would stretch beyond the orbit of Mars.

参宿四是猎户座的一颗红超巨星,猎户座是横跨天球赤道的一个非常显眼的星座。参宿四是夜空中最亮的星体之一,肉眼很容易看到。它的质量大约是太阳的十倍,如果它位于太阳系的中心,它的外边缘将延伸到火星轨道之外。

Betelgeuse shines more brightly than the sun partly because it is bigger and thus has more fuel, but also because it is burning through that fuel faster. As a result, it will die much sooner. The sun is around halfway through its 10bn-year lifespan. Betelgeuse’s span will be about 10m years, and it is close to the end of that period—perhaps very close. For, in the past few weeks, astronomers have watched it getting precipitously dimmer and that has made them wonder: could this be a signal that Betelgeuse’s time has come?

参宿四比太阳更明亮,部分原因是它体积更大,因此有更多燃料,但也是因为它燃烧这些燃料的速度更快。结果,它走向死亡的速度也会快得多。太阳100亿年的寿命已过了大概一半。参宿四的寿命约为1000万年,它已经接近生命尽头了——可能非常近。因为在过去几周里,天文学家们观察到它突然变暗了,他们不禁怀疑这会不会是参宿四大限将至的信号?

When a star such as Betelgeuse runs out of fuel the nuclear reactions in its core which keep it shining stop—and with them the heat and outward radiation pressure needed to balance the force of gravity trying to pull everything inward. At that point, gravity wins. The core collapses. And the resulting shock wave destroys the star in an explosion called a supernova that is temporarily brighter than the rest of Earth’s home galaxy, the Milky Way, put together.

当参宿四这样的恒星耗尽燃料时,让它持续发光的核心核反应会停止,发热也会停止,向外的辐射压力(需要用它来平衡将一切都向内拉的重力)也会随之停止。那一刻,重力赢了。核心坍塌。由此产生的冲击波会在被称作超新星的爆炸中摧毁这颗恒星。超新星的亮度在一段时间内会比地球的母星系银河系其余部分的总亮度还要高。

Brighter than a billion suns

比10亿个太阳还要亮

From Earth, a mere 600 light-years away, a Betelgeuse supernova would be spectacular. It would be visible in the daytime for weeks, as bright as the full Moon at night, and able to cast shadows. The last supernova thought to have had such brightness occurred a millennium ago. For astronomers, it would be an unprecedented opportunity to use their armoury of observatories—electromagnetic, gravitational and neutrino—to study the final moments of a star, close-up, as it collapses.

距离地球只有600光年的参宿四超新星看起来将会非常壮观。连续数周都能在白天见到它,在晚上明亮如满月,还能投射阴影。最近出现的被认为有如此亮度的超新星还是在一千年前。对天文学家来说,这将是一个前所未有的机会,他们可以用电磁、引力和中微子等各式天文台在恒星崩溃时密切观察它的最后时刻。

So far, the closest supernova seen since the telescope was invented is SN1987A, spotted more than three decades ago in the Large Magellanic Cloud, a galaxy 160,000 light-years from the Milky Way. But astronomers detected SN1987A only after it had already happened. They have never been able to bring modern instruments to bear on a supernova in the Milky Way itself, and never watched a star in the moments before and during its final explosion.

直到目前,自望远镜发明以来观测到的距离最近的超新星是30多年前在大麦哲伦星云中发现的SN1987A,这一星云距银河系16万光年。但天文学家是在SN1987A爆炸之后才发现它的。他们从来没能用现代仪器观测过银河系中的超新星,也从来没有观测过恒星终极爆炸之前和爆炸期间的情况。

Betelgeuse is destined to become a supernova soon, that much is certain. But “soon” in astronomical terms could mean anything from today to 100,000 years’ time. If the recent dip in the star’s brightness is not a signal of imminent catastrophe, it could have a number of other explanations. Because the material inside it is always churning as it is heated, Betelgeuse has hotspots on its surface. Sometimes these hotspots are ejected into space, leaving relatively cooler and dimmer areas behind on the star’s surface, and reducing the magnitude of its output of light.

参宿四会很快变成超新星,这是肯定的。但在天文学意义上,“很快”可能是今天,也可能是今天到未来10万年内的任何时间。如果近来参宿四亮度的下降不是大毁灭即将来临的信号,那么也可能有一些别的解释。因为其内部的物质在加热时总在翻腾,所以参宿四的表面有热点。有时这些热点被喷射到太空,在星体表面留下相对较冷和较暗的区域,并且降低它的光输出强度。

On top of these random events, Betelgeuse is also known to be a semi-regular variable star. This means its brightness changes as it pulses up and down in size. As that happens, its surface area increases or decreases proportionally. Since the brightness per square kilometre of a star tends to remain the same during these pulses, a larger surface area means the star will emit more light overall, and a smaller one, less. Various cycles like this operate within Betelgeuse, with periods ranging from a few hundred Earth days to several thousand.

除了这些随机事件外,我们还知道参宿四是一颗半规则变星。这意味着它的亮度会随大小的变化而变化。当这种情况发生时,它的表面积成比例地增加或减少。由于恒星每平方公里的亮度在这些变化期间趋于保持不变,更大的表面积意味着恒星整体将发出更多的光,而更小的表面积则发出更少的光。参宿四内有着多个这样的周期,时长从几百到几千个地球日不等。

Astronomers will continue watching the star over the coming weeks. Most, realistically, expect it to brighten up again as the internal cycles continue. But even if there is no supernova this time around, that merely postpones the day when Betelgeuse will undergo a real-world equivalent of the Great Collapsing Hrung Disaster.■

天文学家将在未来几周内继续观测这颗星。大多数人都抱着比较现实的预期:随着内部周期的继续,它会再次亮起来。但是,即使这次没有超新星爆发,也只是推迟了参宿四在现实中上演“异物大坍塌”的那一天。

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