跟读练习: The Black Hole That Kills Galaxies - Quasars - 通过视频学习英语口语
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The universe looks like a vast empty ocean sprinkled with the rare islands of galaxies..
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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.
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Like the roots of some massive tree, gas spreads out from each galaxy, gravity funneling fresh mass into this dense, cosmic forest.
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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.
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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.
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What are they, and how do they mold the structure of the universe at their whim?
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Everywhere You Look, Weird Things in the Sky In 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.
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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.
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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.
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Monsters, exploding and screaming into the void with a violence not thought possible before.
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As we mapped the sky, we discovered over a million quasars. And they all seemed to be very far away.
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Looking into space, far away means very long ago, because their 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.
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Let’s go back in time, just 3 billion years after the big bang and see what was going on back then.
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The Incredible Power of Quasars How could an early baby galaxy be so incredibly bright and violent?
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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.
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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.
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But how can the brightest things in the universe be black holes, which trap anything and everything that crosses their event horizon?
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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.
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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.
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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.
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Collisions between particles and friction heat it up to hundreds of thousands of degrees.
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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.
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This is what a quasar is, a super massive black hole having a feast.
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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.
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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.
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But quasars can’t eat for long, maybe a few million years, because their feast ultimately kills their galaxy.
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How Quasars Kill Galaxies Okay, 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.
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Hot gas cannot form stars. This sounds odd, because 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.
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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.
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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.
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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. And gas that leaves will mix with gas coming back in and recycle it back into the galaxy. 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?
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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.
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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. But sadly we don’t know its ancient history.
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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.
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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.
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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.
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But you don’t have to wait that long. There are already plenty of fascinating things to explore right here on this planet, right now – if you have the knowledge to understand them.
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To help you with that, we’ve created a series of lessons to take your scientific knowledge to the next level. Made in collaboration with our friends at Brilliant.org, these lessons give you a deeper understanding of the topics from our most popular videos, from rabies and mammalian metabolism, to climate science. There's also a lesson on black holes, where you can delve into the fundamental principles behind their formation and behavior. A deeper understanding will also help you appreciate their role in powering the quasars we talked about in this video.
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Brilliant is an interactive learning tool that makes math, science, and computer science accessible with a hands-on approach. Because we know that to really learn something, you’ve got to do it. Think of each lesson as a one-on-one tutoring version of a Kurzgesagt video.
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We love seeing how the gears interlock with our research – Brilliant gives you the tools to understand how everything fits together.
为什么要用这个视频进行口语练习？
观看关于“吞噬银河系的黑洞：类星体”的视频，不仅可以让你领略宇宙的奥秘，还可以在这个过程中提高你的英语口语能力。通过模仿视频中的讲话者，一方面你可以提升自己的语言表达能力，另一方面也能提高英语发音。运用“shadow speech”技巧，即边听边说，有助于加深你对复杂科学概念的理解，同时培养流利的英语口语。这种方法使你更容易掌握音调、节奏和语调，从而提高英语口语练习的效果。
语法与表达的语境分析
在这个视频中，讲解者使用了多种重要的表达和语法结构，这些都非常适合用在我们的英语口语练习中。以下是几处关键点：
- 被动语态：如“黑洞被认为是…” 这种结构有助于突出事件的重要性，适用于讨论科学现象。
- 条件句：诸如“如果…那么…”的句型常用于假设情境，能够帮助你在对话中更灵活地表达观点。
- 现在分词与动名词：视频中提到“…的能量释放…”等表达，通过这种结构，能有效地连接不同的信息，使句子更加丰富。
- 对比和转折：例如“虽然…但是…”的用法，可以让你的口语更显专业，增加表达的层次感。
常见的发音陷阱
在学习英语口语时，掌握发音是至关重要的。在这个视频中，有些词汇和短语可能会给学习者带来挑战：
- Quasar（类星体）：这个词的重音可能会让人感到困惑，正确的读音应为 /ˈkweɪ.zɑːr/。
- Gravity（重力）：许多非母语者在发音时可能会忽略/p/的声音，正确读作 /ˈɡræv.ɪ.ti/。
- Cosmos（宇宙）：常见的发音错误包括元音的拖音，正确方法是将其读作 /ˈkɒz.mɒs/。
在练习这些发音时，可以运用“提高英语发音”的方法，通过反复模仿讲解者的语调和节奏，以达到在实际对话中更自然流畅的效果。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。