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  • See that strip of stars

  • splashed across the night sky?

  • That's our home galaxy, the Milky Way.

  • You can see it from Earth

  • because we live right on the outskirts,

  • far away from all the fun stuff

  • happening in its center.

  • The Milky Way is huge -

  • about 100,000 light-years across.

  • It has four large, spiral arms encircling its center.

  • That makes it a barred spiral galaxy,

  • just like most galaxies in the observable universe.

  • If the Earth packed up its belongings

  • and moved to the heart of the Milky Way,

  • things would be looking pretty bleak

  • for the survival of any kind of life on the planet.

  • But not because of the Milky Way's supermassive black hole...

  • The Earth is located in a quiet neighborhood

  • in one of the smallest spurs of the Milky Way - the Orion Arm.

  • We've got approximately 27,000 light-years

  • between us and the galactic center.

  • It's a comfortable spot to live in.

  • The temperatures on Earth are just right to sustain life.

  • And there aren't too many space hazards that could wipe out our existence.

  • I didn't say it's completely safe, did I?

  • Living anywhere near the center of the Milky Way would be... different.

  • It would depend on what part of that center

  • the Earth had the misfortune to occupy.

  • The closer you get to the heart of the galaxy,

  • the tighter the stars are packed together.

  • Because of this high star density, the Earth would be blasted

  • with a lot more radiation than what the Sun throws at you right now.

  • Under these circumstances, the odds of life

  • ever evolving would be pretty small.

  • But if the Earth moved to the center together with all its inhabitants,

  • you'd find yourself very unlucky.

  • Earth's magnetosphere wouldn't be able to protect you

  • from space radiation blasting from all directions.

  • This could change the Earth's climate,

  • and cause everything on the planet to either mutate or die.

  • If you lived, your biggest concern would be

  • a close encounter with a supernova.

  • A supernova occurs when a massive star collapses

  • releasing radio waves, X-rays, cosmic rays and gamma rays into space.

  • For all we know, one massive stellar body

  • could throw the Earth out of the Sun's orbit.

  • Our planet would be surrounded by foreign stars

  • until one of them exploded in a supernova and wiped us out for good.

  • But it would look spectacular from Earth,

  • if only for a brief moment.

  • There's another big hazard that lies within the Milky Way's center -

  • a supermassive black hole called Sagittarius A*.

  • If getting sucked into a black hole isn't on your to-do list,

  • consider yourself lucky.

  • The Earth might stay far enough from it

  • that we wouldn't get engulfed by this cosmic beast.

  • But we could get close enough to get caught in the black hole's orbit.

  • At a distance of 20 billion km (12 billion mi)

  • from the black hole's event horizon,

  • the Earth could develop a speed of 25 million km/h (15.5 million mph).

  • That's over 230 times faster

  • than the speed our planet is moving at right now.

  • It sure wouldn't be good for you,

  • or anything else on the Earth's surface.

  • The Earth is perfectly designed to be right where it is.

  • It can survive on the outskirts of the galaxy,

  • but you wouldn't want it to be anywhere else.

  • The most dangerous place for a planet to be located

  • is anywhere near the center of a galaxy - any galaxy.

  • If you want a nice view,

  • your best bet might be to teleport the Earth to the middle of a nebula instead.

  • But that's a story for another WHAT IF.

See that strip of stars

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地球が天の川の中心付近にあったら? (What If Earth Was Near the Center of the Milky Way?)

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    林宜悉 に公開 2021 年 01 月 14 日
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