Name: 科学者たちが宇宙を横断する1つのニュートリノを追跡した理由 (Why Scientists Tracked One Neutrino Across the Universe)
Uploaded: 2021-01-14T10:38:08.000Z
Duration: 6 min 9 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Last week, two papers published in the journal Science unveiled some huge news in the world of astrophysics,

featuring the tiniest particles in the universe.

More than 1000 authors from nearly 20 research institutions spanning the globe

announced that they've likely identified the very first astrophysical source of high-energy neutrinos.

This is the first evidence toward solving a century-old mystery about the source of certain cosmic rays.

And some are even calling it the dawn of a new era in astronomy…

and they constantly rain down on Earth from a variety of outer space sources.

Most come from the Sun, but a few super high energy ones come from places outside the galaxy.

Until now, though, astronomers haven't had evidence

to show exactly what objects are launching them in our direction.

Hypotheses have included violent events like supernovas, colliding galaxies, or merging black holes,

but it's really hard to identify a source.

That's because cosmic particles are electrically charged,

so they don't travel in straight lines from where they were born to our detectors.

Their trajectories are affected by any kind of magnetic field.

And it's not like the universe has a shortage of magnetic fields.

So instead, researchers have been trying to understand cosmic rays

by looking at another kind of particle called neutrinos.

Specifically, high-energy ones, or those with energy values too high to be produced by any device on Earth.

These neutrinos are created when high-energy cosmic rays interact with things like nearby gas.

And because they don't have an electric charge, they aren't affected by magnetic fields.

So if astronomers could detect some of these neutrinos on Earth,

they could trace them back to their source, and pinpoint what was creating the original cosmic rays.

Then again, detecting these particles isn't exactly easy, either.

They're by far and away the least massive particles known to physics.

Like, every second, trillions of them are passing through your body

and they can stream through entire planets as if there's nothing there.

But back in 2017, researchers struck gold.

On September 22, a single high-energy neutrino interacted with the IceCube Neutrino Observatory down in Antarctica.

One of this detector's main jobs is to track down these kind of particles, and to do it,

it uses over 5000 sensors arranged in a 3-dimensional grid.

It's also buried more than 1.4 kilometers beneath the icy surface to avoid interference.

When high-energy neutrinos collide with the atoms in or near the detector,

they make secondary charged particles, which produce blue light that's detected by IceCube's grid.

Since 2013, the experiment has only detected a few dozen high-energy neutrinos,

and they've appeared to be arriving from random directions.

So astronomers weren't able to pin down any obvious sources.

Astronomers were able to narrow this neutrino's origin in space

to 1 degree in the sky off the left shoulder of the constellation Orion.

It doesn't sound like much, but that's about twice the size of the Moon as seen from Earth.

And in that area of space, teams found 637 objects that might be responsible for the IceCube neutrino.

Still, with enough data matching, and time spent hunting,

follow-up observations were able to narrow all that down to a single source: a flaring blazar about 4 billion light-years from Earth

Because its full name is TXS 0506+056, and no one wants to mess with that.

Blazars are a special kind of quasar, and they're some of the brightest objects in the entire universe.

They're also called blazars, which is great.

Quasars in general are the central cores of certain galaxies,

ones housing a supermassive black hole that's actively gobbling up matter.

As that matter spirals down into the belly of the beast, it emits a lot of radiation,

so much that the core can outshine the light of all the stars in the galaxy a thousand-fold.

Some quasars also have magnetic fields that accelerate particles away at near light-speeds

And blazars are those that have a jet pointed close to straight at us.

Now, it looks like they're also one confirmed source of cosmic rays.

Thanks to work by hundreds of scientists, we were somehow able to track one tiny particle

from a detector in Antarctica all the way across the universe to a specific blazar.

Of course, there is a chance that the neutrino didn't actually come from some blazar'scosmic rays.

But you can make a good case that it did.

When astronomers looked back at older IceCube data,

they did find evidence that other neutrinos came from the same place,

during events when the blazar was 'acting up' so to speak.

Stuff like emitting extra bursts of gamma rays.

A statistical analysis also showed that the chance that the events are unrelated is about 1 in 5000.

Those are pretty great odds, but it's also not impossible that we're wrong.

So this massive team of astronomers has to keep hunting.

So far, though, these results show the possibilities of what the field calls multimessenger astronomy,

using not just light, but neutrinos or even gravitational waves to study the same object.

Because neutrinos basically treat matter like it's nothing,

measurements of them coming from things like blazars and black holes could reveal more about how those objects work.

We could learn things like the actual physics behind these beams of cosmic rays,

even in environments where other research methods won't cut it.

So as we keep making discoveries like this,

we'll be able to probe deeper into mysterious areas of physics than ever before.

And we at SciShow Space are eagerly waiting for what's to come.

And thanks for watching this episode of SciShow Space News!

We could not bring you new information from around the universe every week

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