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  • This episode is sponsored by Squarespace.

  • From websites and online stores to marketing tools and analytics,

  • Squarespace is the all-in-one platform to build a beautiful online presence and run your business.

  • [♪ INTRO]

  • For years, scientists have been studying a group of galaxies that shatters records.

  • They're classified as elliptical galaxies,

  • since they're elliptical in shape and don't have any recognizable structure.

  • But unlike the billions of other ellipticals out there, these things are ancient, dense,

  • and more massive than any group of galaxies we've ever seen.

  • They contain up to ten times the number of stars in the Milky Way.

  • And not only are they record-holders, but for a long time,

  • scientists couldn't even figure out how they existed in the first place.

  • They didn't fit into the usual models for how ellipticals form.

  • And it wasn't until researchers uncovered a clue at the edge of the universe

  • that they could finally tell the story of how the most massive galaxies came to be.

  • Normally, elliptical galaxies form when spiral-shaped galaxies

  • like the Milky Way collide and merge together.

  • But studies of some of the most massive ellipticals show that about half of them

  • had already finished forming by three billion years after the Big Bang.

  • And most spiral galaxies didn't exist until later.

  • So it's pretty clear that these things didn't come about through the usual mergers.

  • That wasn't the only strange thing about them, though.

  • The stars in these ancient neighborhoods are also packed incredibly tightly:

  • between ten and a hundred times denser than in other ellipticals.

  • And at first, astronomers couldn't figure out why that would happen, either.

  • This mystery finally began to unravel in the 1990s,

  • when scientists first figured out how to study the universe with submillimeter radiation.

  • Submillimeter wavelengths are longer than visible and infrared waves,

  • but shorter than radio waves.

  • They're often really tricky to observe from Earth

  • because our atmosphere absorbs most of them.

  • But in the late '90s, we finally developed the tools to study them.

  • In 1998, astronomers used a new camera on the James Clerk Maxwell Telescope in Hawai'i

  • to create the first highly detailed picture of our universe at submillimeter wavelengths.

  • And it revealed new, incredibly distant galaxies shining brightly with submillimeter radiation.

  • They were at the very edge of the observable universe,

  • and were some of the oldest galaxies we'd ever seen.

  • No one had discovered them before because these things

  • were almost completely dark at the visible wavelengths.

  • They released a ton of submillimeter radiation, though, because they're incredibly dusty.

  • The visible light coming off their stars gets absorbed by the surrounding dust,

  • and that heats up and re-emits the light at longer wavelengths,

  • mostly in the submillimeter range.

  • These objects came to be called, creatively, submillimeter galaxies.

  • Scientists think they formed when galaxies in the early universe grew massive enough

  • to pull in huge amounts of gas and dust from their surroundings.

  • This discovery turned out to be huge, not just because it was a new type of galaxy,

  • but because it eventually helped us crack the secret of those ridiculously massive ellipticals.

  • See, aside from making them invisible,

  • all of that dust also makes these submillimeter galaxies really active star-forming regions.

  • New stars are being born there thousands of times faster than in the Milky Way,

  • which puts out a measly one or two stars a year.

  • And with so much star formation happening,

  • scientists predicted that these galaxies would quickly burn themselves out.

  • In the end, they'd become compact elliptical galaxies with densely packed stars.

  • If you think that's starting to sound familiar, you're not the only one.

  • Apart from their density, further studies revealed that these

  • submillimeter galaxies are eerily similar to today's most massive elliptical galaxies.

  • Like, a 2014 study even found that their stars have many of the same characteristics.

  • That suggests that these dusty neighborhoods

  • are precursors to the massive elliptical ones.

  • And from there, the rest of the story pretty quickly fell into place.

  • Further modeling showed that the stars in submillimeter galaxies formed super fast,

  • with star formation pretty much done in forty million years; a cosmic blink of the eye.

  • Over the next few billion years, these compact elliptical galaxies wandered the universe,

  • tugged here and there by the faint pull of gravity from other galaxies.

  • Now and then, close enough encounters led to collisions.

  • Galaxies merged, mixing together their stars and creating much larger,

  • but still incredibly dense, elliptical galaxies.

  • And with that, the universe's giant elliptical galaxies were born,

  • with dense cores made from stars several billion years older than the galaxy itself.

  • This appears to finally solve the mystery of where the universe's most massive galaxies came from,

  • and it's a huge step toward understanding the evolution of structure in our universe.

  • It's also a reminder of just how many clues are likely out there, sitting in the dark,

  • waiting for the right leap of technology to expose them.

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  • It offers customizable content layout,

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  • You can also schedule your posts so they go out whenever you're ready.

  • And if you run a small business, Squarespace also

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  • [♪ OUTRO]

This episode is sponsored by Squarespace.

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B2 中上級

最大の銀河はどこから来るのか? (Where Do the Biggest Galaxies Come From?)

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    林宜悉 に公開 2021 年 01 月 14 日
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