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  • Black holes are among the most destructive objects in the universe.

  • Anything that gets too close to the central singularity of a black hole,

  • be it an asteroid, planet, or star,

  • risks being torn apart by its extreme gravitational field.

  • And if the approaching object happens to cross the black hole’s event horizon,

  • itll disappear and never re-emerge,

  • adding to the black hole’s mass and expanding its radius in the process.

  • There is nothing we could throw at a black hole

  • that would do the least bit of damage to it.

  • Even another black hole won’t destroy it

  • the two will simply merge into a larger black hole,

  • releasing a bit of energy as gravitational waves in the process.

  • By some accounts,

  • it’s possible that the universe may eventually consist entirely of black holes

  • in a very distant future.

  • And yet, there may be a way to destroy, orevaporate,” these objects after all.

  • If the theory is true,

  • all we need to do is to wait.

  • In 1974,

  • Stephen Hawking theorized a process

  • that could lead a black hole to gradually lose mass.

  • Hawking radiation, as it came to be known,

  • is based on a well-established phenomenon called quantum fluctuations of the vacuum.

  • According to quantum mechanics,

  • a given point in spacetime fluctuates between multiple possible energy states.

  • These fluctuations are driven by the continuous creation and destruction

  • of virtual particle pairs,

  • which consist of a particle and its oppositely charged antiparticle.

  • Normally, the two collide and annihilate each other shortly after appearing,

  • preserving the total energy.

  • But what happens when they appear just at the edge of a black hole’s event horizon?

  • If theyre positioned just right,

  • one of the particles could escape the black hole’s pull

  • while its counterpart falls in.

  • It would then annihilate another oppositely charged particle

  • within the event horizon of the black hole,

  • reducing the black hole’s mass.

  • Meanwhile, to an outside observer,

  • it would look like the black hole had emitted the escaped particle.

  • Thus, unless a black hole continues to absorb additional matter and energy,

  • itll evaporate particle by particle, at an excruciatingly slow rate.

  • How slow?

  • A branch of physics, called black hole thermodynamics, gives us an answer.

  • When everyday objects or celestial bodies release energy to their environment,

  • we perceive that as heat,

  • and can use their energy emission to measure their temperature.

  • Black hole thermodynamics

  • suggests that we can similarly define thetemperatureof a black hole.

  • It theorizes that the more massive the black hole,

  • the lower its temperature.

  • The universe’s largest black holes

  • would give off temperatures of the order of 10 to the -17th power Kelvin,

  • very close to absolute zero.

  • Meanwhile, one with the mass of the asteroid Vesta

  • would have a temperature close to 200 degrees Celsius,

  • thus releasing a lot of energy in the form of Hawking Radiation

  • to the cold outside environment.

  • The smaller the black hole,

  • the hotter it seems to be burning

  • and the sooner itll burn out completely.

  • Just how soon?

  • Well, don’t hold your breath.

  • First of all, most black holes accrete, or absorb matter and energy,

  • more quickly than they emit Hawking radiation.

  • But even if a black hole with the mass of our Sun stopped accreting,

  • it would take 10 to the 67th power years

  • many many magnitudes longer than the current age of the Universe

  • to fully evaporate.

  • When a black hole reaches about 230 metric tons,

  • itll have only one more second to live.

  • In that final second,

  • its event horizon becomes increasingly tiny,

  • until finally releasing all of its energy back into the universe.

  • And while Hawking radiation has never been directly observed,

  • some scientists believe that certain gamma ray flashes detected in the sky

  • are actually traces of the last moments

  • of small, primordial black holes formed at the dawn of time.

  • Eventually, in an almost inconceivably distant future,

  • the universe may be left as a cold and dark place.

  • But if Stephen Hawking was right,

  • before that happens,

  • the normally terrifying and otherwise impervious black holes

  • will end their existence in a final blaze of glory.

Black holes are among the most destructive objects in the universe.

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ブラックホールは破壊できるのか?- ファビオ・パクッチ (Can a black hole be destroyed? - Fabio Pacucci)

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    林宜悉 に公開 2021 年 01 月 14 日
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