シャドーイング練習: The Black Hole That Kills Galaxies - Quasars - 動画で英語スピーキングを学ぶ
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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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We love seeing how the gears interlock with our research – Brilliant gives you the tools to understand how everything fits together.
文脈と背景
この動画は、「銀河を殺すブラックホール - クエーサー」というテーマで、宇宙における非常に強力な天体であるクエーサーについて説明しています。クエーサーは、非常に遠くに位置し、強力な重力を持つ超巨大ブラックホールが中心にある銀河の活発なコアであり、これにより周囲の宇宙を形作る役割を果たしています。この動画は私たちに宇宙におけるクエーサーの重要性や、彼らがどのように銀河の形成に影響を及ぼすのかを理解する手助けをします。
日常コミュニケーションのためのトップ5フレーズ
- クエーサーは銀河の中心にあります。
- 彼らは非常に明るく、数兆個の星の力で輝いています。
- クエーサーは銀河を破壊することができます。
- 彼らは非常に遠くにあり、膨張する宇宙の影響を受けています。
- クエーサーは超巨大ブラックホールの餌になっています。
段階的なシャドーイングガイド
この動画を使った英語スピーキング練習は、特にshadowspeakやshadow speakを活用する際に効果的です。以下のステップに従って、動画内容をスムーズに理解し、発音やイントネーションを改善しましょう：
- まず、動画を全体的に観て内容を把握します。始めに動画のテーマを理解することで、文脈がわかります。
- 次に、重要なフレーズをリストアップします。上記の「トップ5フレーズ」を参考に自分でメモを取りながら聴きましょう。
- その後、英語シャドーイングにチャレンジします。動画のフレーズを少しずつ繰り返すことで、自分の発音を改善できます。
- 何度も聴き直し、声に出して話す練習をしましょう。このプロセスを通じて、YouTubeで英語学習がより効果的になります。
- 最後に、フレーズを使ったダイアログを作成し、自分の言葉で表現してみましょう。これにより、実際の会話でも使えるスキルが身につきます。
この方法を繰り返し行うことで、あなたの英語スピーキング練習が楽になり、流暢さが増すでしょう。興味を持って楽しみながら学んでください！
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。