Name: 天文学者が史上最大の爆発を発見 (Astronomers Just Discovered the Biggest Explosion Ever)
Uploaded: 2021-01-14T10:28:11.000Z
Duration: 6 min 28 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：

astronomers have been puzzling over a strange feature in the galaxy cluster Ophiuchus

It looked kind of like a crater in the gas surrounding one of the galaxies

astronomers published a paper in The Astrophysical Journal

announcing that it was caused by the largest explosion we've ever detected!

Which kind of seems like something that'd be hard to keep under wraps.

But even though astronomers have been looking at the remnants of this explosion for four

it wasn't always obvious what they were looking at.

a collaboration of astronomers based at Stanford first saw something fishy

when they analyzed data from the Chandra X-Ray Observatory.

The cluster is about 390 million light-years away,

and it has a whole bunch of galaxies surrounded by dust and gas.

toward the center of the cluster with a supermassive black hole in its center.

In their images, they saw a sharp, curved line around that galaxy,

it looked like a lot of the gas had just been scooped out.

Now, a feature like this wasn't totally unheard of.

that they were looking at cavities left over by outbursts from black holes.

So this team thought, maybe this was similar—

to see what it would take to carve out a cavity that size,

they found it would have had to be five times more energetic

than the largest known explosion at the time.

And they didn't think that was too likely.

probably would have destroyed the cool gas surrounding the core of this galaxy,

But they still couldn't figure out what was causing this weird feature.

So a second team of researchers picked up where they left off.

This team, based at the Naval Research Laboratory in Washington, D.C.,

they used X-ray data from ESA's XMM-Newton satellite

they also looked at radio data from the Murchison Widefield Array in Australia

and from the Giant Metrewave Radio Telescope in India.

That radio data revealed loads of electrons inside the cavity

accelerated to near the speed of light—

fast enough to emit their own radio waves.

And electrons don't just take off at relativistic speeds

without something really strong accelerating them.

So, looking at this big ol' hole punched out of the gas,

this team could be pretty sure what they were looking at:

an outburst from a supermassive black hole.

sometimes matter doesn't fall in but instead gets accelerated to relativistic speeds

and shot back into space in a huge burst of energy.

Astronomers have observed bursts like this before,

The explosion they were looking at was truly gigantic—

and five times larger than the previous record-holder!

With lots of these bursts, any cool gas around the core of the galaxy can be destroyed,

which is why the first team had ruled out the possibility of an explosion.

the temperature and density of the gas drops off especially quickly with radius,

which might have made it more resilient to a large burst—

The cool thing about this discovery is not just that it's a huge explosion in space—

though that is also cool - it also illustrates how science builds upon itself.

The second team was only able to make this incredible discovery

because another team had tackled it first.

They used some of the same data and calculations—

just a few years and a few thousand miles apart!

last week we also got an update in cute astronomy news:

scientists think it's been orbiting us for about three years—

we've probably just been missing it because it's so small.

It's only the second time we've ever spotted a natural object

other than the Moon in orbit around the Earth.

But scientists have pointed out that this isn't actually a super-rare phenomenon.

Since everything in the solar system is constantly in motion,

planets capture small objects all the time.

Astronomers estimate that at any given point,

there's probably at least one meter-sized rock orbiting the Earth.

But they can be really hard to detect because they're usually very small,

and they don't tend to stick around for long.