外刊精读 | “杀死”星系的黑洞|引力|恒星|类星体|galaxies

今天是小芳老师陪你精读外刊的第226天泛读原文（盲听1遍，泛读1遍，对照文本听1遍）When it comes to first impressions, we all want to make a good one. And that’s why we tend to focus on our best traits and qualities. However, we often fall into the trap of thinking that everything about us needs to be perfect. But that’s just unrealistic. We all have imperfections. It’s part of being human. And while it’s easy to believe that our ‘supposed flaws and imperfections’ make us less attractive, here are some that can actually make us seem more appealing to others:The universe looks like a vast empty ocean sprinkled with rare islands of galaxies. But this is an illusion: just a small fraction of all atoms are found in galaxies, while the rest is thought to be drifting in between in the intergalactic medium. Like the roots of some massive tree, gas spreads out from each galaxy, gravity funneling fresh mass into this dense, cosmic forest. Here in the intergalactic medium are the raw materials of creation: hydrogen and helium, woven into sheets and filaments that flow into galaxies where they eventually create stars.But if we look closely, we see who is actually in charge: quasars, the single most powerful objects in existence. As small as a grain of sand compared to the amazon river, they reside in the centers of some galaxies, shining with the power of a trillion stars, blasting out huge jets of matter, completely reshaping the cosmos around them. They are so powerful that they can kill a galaxy. What are they, and how do they mold the structure of the universe at their whim?Everywhere You Look, Weird Things in the SkyIn the 1950s, astronomers noticed mysterious loud radio-waves coming from spots all over the sky. They were named “quasi-stellar radio sources”, or “quasars” because they were dots like stars, but were seen in radio waves rather than visible light. Everything about them was strange. Some flickered, others emitted high energy X-rays in addition to radio waves, but all seemed to be tiny. They also moved extremely fast, as much as over 30% the speed of light. The only explanation was that they must have been so distant that their apparent speed was actually the expansion of the universe moving them away from us. But these enormous distances meant that quasars couldn’t just be stars, but the active cores of galaxies billions of lightyears away! And it gets crazier. To appear so bright and loud, given these vast distances, they are thousands of times brighter than the entire Milky Way – monsters, exploding and screaming into the void with a violence not thought possible before.As we mapped the sky, we discovered over a million quasars. And they all seemed to be very far away. Looking into space, far away means very long ago, because light takes so long to reach us. Quasars were common in the early universe, having peaked in number 10 billion years ago when galaxies, and the universe itself was still very young. Let’s go back in time, just 3 billion years after the Big Bang and see what was going on back then.The Incredible Power of QuasarsHow could an early baby galaxy be so incredibly bright and violent? All that light and radiation couldn’t be stars, as there weren’t nearly enough of them. And since galaxies tend to grow with time by merging, the starlight from small galaxies shouldn’t be far brighter than any galaxy today. There’s only one way to generate the vast amounts of energy a quasar shines with: feeding supermassive black holes. We still don’t know how exactly they formed, but it seems that every galaxy has one in their center. But how can the brightest things in the universe be black holes, which trap anything and everything that crosses their event horizon?Well, the light of a quasar is not coming from inside these black holes. Rather, it comes from the space around them, a massive orbiting disk of gas called an ‘accretion disk.’ Quasars use the same fuel as stars to shine: matter. It is just that black holes are the most efficient engines for converting matter into energy in the universe. The energy released by matter falling into a black hole can be 60 times greater than that released by nuclear fusion in the core of a star because the energy released by a black hole comes from gravity, not from nuclear reactions.Matter falling into a black hole speeds up to almost the speed of light before it crosses the event horizon, buzzing with an incredible amount of kinetic energy. Of course, once inside the black hole, it takes that energy with it. You only get to witness this energy if you drop your matter in the right way. Fall straight down and the outside universe gets nothing. But when you have a lot of matter, it spirals in incredibly fast towards the event horizon forming a disk. Collisions between particles and friction heat it up to hundreds of thousands of degrees.In a space not much bigger than our solar system, the core of a galaxy can release many times more energy than all its stars combined. This is what a quasar is, a super massive black hole having a feast. And these black holes eat a lot. Typical quasars consume one to a hundred Earth masses of gas per minute! Ten billion years ago, the universe was about a third of its current size, so the intergalactic medium was much less spread out, meaning the filaments of gas around quasars could feed them a banquet, making them vomit insane amounts of light and radiation.The brightest quasars power jets, tangling the magnetic field of the matter around them into a narrow cone. Like a particle accelerator, they launch enormous beams of matter out, plowing through the circumgalactic medium, forming plumes of matter that grow to hundreds of thousands of lightyears in size. It’s almost unfathomable in scale – a tiny spot in a galaxy carving out patches of the universe 100,000s of light years long.But quasars can’t eat for long, maybe a few million years, because their feast ultimately kills their galaxy.How Quasars Kill GalaxiesOkay, maybe “killing” is a bit of an exaggeration. A galaxy is still there after its quasar turns off. But it will never be the same again. Quasars, being among the hottest and brightest things in the universe, break their galaxies by heating them up too much and stopping star formation. Stars are gas that collapsed in on itself and then got really hot. But in a cloud of gas that is already hot, atoms are moving quickly. When they collide, they hit hard, exerting pressure that resists gravity’s squeeze – so hot gas can’t form stars. Instead, the best gas for forming stars is already cold, and won’t put up a fight when it’s time to collapse into a star.On top of that, quasars push gas out of their galaxies. Not only does this starve the quasar, but its galaxy loses the raw materials for new stars. As sad as this sounds, it might be a good thing for life. The alternative can be far more dangerous: too many stars.New stars forming is usually followed by massive stars exploding in supernovae, so planets would be burned sterile. But of course, it’s more complicated. Like the intricacies of our own planet’s biosphere, every piece of the galaxy is dependent on and influencing every other part of the galactic environment. While hot things, like quasars and supernovae, tend to push gas out of the galaxy, shockwaves and quasar jets can also compress gas, making new stars at least for a short time. But in general, we can say that without things becoming a bit more chill, we would not exist today, which brings us to our final question:Did the Milky Way Have a Quasar in the Past?It’s unclear if every galaxy went through a quasar phase, but understanding distant quasars may provide clues to the history of the Milky Way. Galaxies don’t do a good job of preserving their history. Like sand on a beach, the endless churning mixes away the clues to their past. It’s possible the Milky Way was once a quasar, which may have allowed our supermassive black hole Sagittarius A star to have grown to 4 million times the mass of the sun. And as dormant as it is now, Sagittarius A star could turn into a quasar in the future. In a few billion years, the Milky Way will merge with Andromeda. We’ve seen over a hundred ‘double quasars’ in galaxies smashing together, where fresh gas is provided for the central black holes.But it won’t last for long. When galaxies merge, so do their super massive black holes, sinking into the center of their new galaxy, kicking up dust and stars in every direction. We don’t know whether this will happen, but it would truly be an incredible sight. Maybe some beings in the far future are going to witness it and be in awe of what they see.精读原文When it comes to first impressions, we all want to make a good one. And that’s why we tend to focus on our best traits and qualities. However, we often fall into the trap of thinking that everything about us needs to be perfect. But that’s just unrealistic. We all have imperfections. It’s part of being human. And while it’s easy to believe that our ‘supposed flaws and imperfections’ make us less attractive, here are some that can actually make us seem more appealing to others:重点词汇：1. Universe - 宇宙2. Galaxies - 星系3. Intergalactic - 星系间的4. Quasars - 类星体5. Raw materials - 原材料6. Hydrogen - 氢7. Helium - 氦8. Black holes - 黑洞9. Expansion - 膨胀10. Supernovae - 超新星例句与翻译：1. The universe is vast and full of mysteries. (宇宙广阔而充满奥秘。)2. Galaxies are large systems of stars, gas, and dust held together by gravity. (星系是由恒星、气体和尘土通过引力相互牵引在一起的巨大系统。)3. The intergalactic medium is the space between galaxies where atoms are thought to be drifting. (星系间介质是一无所有的星体之间的空间，其中的原子被认为是漂浮其间。)4. Quasars are extremely powerful objects found in the centers of galaxies. (类星体是在星系中心发现的极为强大的物体。)5. Hydrogen and helium are the primary raw materials for creating stars. (氢和氦是创造恒星的主要原材料。)6. Black holes are regions in space where gravity is so strong that nothing, not even light, can escape. (黑洞是空间中引力如此强大以至于什么都逃不出的区域，即使是光也不能。)7. The universe is constantly expanding, with galaxies moving away from each other. (宇宙在不断膨胀，星系彼此相隔越来越远。)8. Supernovae are powerful explosions that occur at the end of a star's life. (超新星是恒星生命周期末期发生的强大爆炸。)长难句解析：1. But these enormous distances meant that quasars couldn’t just be stars, but the active cores of galaxies billions of lightyears away!(但是这些巨大的距离意味着，类星体不能仅仅是恒星，而是位于数十亿光年远的星系的活动核心！)- 这是一个复合句，主句为"But these enormous distances meant that quasars couldn’t just be stars"，从句是"but the active cores of galaxies billions of lightyears away"。- 从句中，"the active cores of galaxies"为主语，"billions of lightyears away"为定语。- 主句和从句通过连词"but"连接，表示对比关系。2. The energy released by matter falling into a black hole can be 60 times greater than that released by nuclear fusion in the core of a star because the energy released by a black hole comes from gravity, not from nuclear reactions.(物质落入黑洞时释放的能量可以比恒星核心的核聚变释放的能量大60倍，因为黑洞释放的能量来自于重力，而不是核反应。)- 这是一个复合句，主句为"The energy released by matter falling into a black hole can be 60 times greater than that released by nuclear fusion"，从句为"because the energy released by a black hole comes from gravity, not from nuclear reactions"。- 主句中的"that released by nuclear fusion in the core of a star"是对前面句子中的能量进行具体解释。- 从句中的"because"表示原因关系，解释黑洞能量释放的原因。多项选择阅读理解题目：1. What is the intergalactic medium made of?A. GalaxiesB. Hydrogen and heliumC. QuasarsD. Supernovae2. What are quasars?A. Small stars found in galaxiesB. Massive supernovae explosionsC. Powerful objects in the centers of galaxiesD. Gas and dust held together by gravity3. How do quasars affect their galaxies?A. They heat up the galaxies and stop star formation.B. They push gas out of the galaxies, preventing the formation of new stars.C. They create shockwaves and jets that compress gas and form new stars.D. They merge with other galaxies and cause the formation of double quasars.滑动查看答案答案BCA【特别声明】以上内容由小芳老师原创整理，转载请注明来源，本平台采用的音视频资源均出于传递信息和英语学习之目的，并没有任何商业目的。本公号尊重知识产权，如无意中侵犯了您的权益，请及时联系后台，本公号将及时删除。