Name: 銀河系中的超大品質黑洞 (Supermassive Black Hole in the Milky Way Galaxy)
Uploaded: 2021-01-14T04:41:47.000Z
Duration: 20 min 9 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

From a distance, our galaxy would look something like this.

A flat spiral, some 100,000 light years across, with pockets of gas, clouds of dust, and about

400 billion stars rotating around the galaxy's center.

That center - bulging up and out of the galactic disk - is tightly packed with stars.

Thick dust and blinding starlight have long obscured our vision into the mysterious inner

And yet, the clues have been piling up, that something important...something strange...

The first to take notice was the physicist Karl Jansky back in the 1930s.

He was asked by his employer, Bell Telephone Labs, to investigate sources of static that

might interfere with what it saw as the killer app of its time... radio voice transmissions.

Using this ungainly radio receiver... Jansky methodically scanned the airwaves. He documented

thunderstorms, near and far... and another signal he could not explain.

It sounded like steam - a hiss of radio noise. Jansky narrowed it to a spot in the constellation

of Sagittarius, in the direction of the center of the galaxy.

Located within a larger pattern of radio emissions...  ... Jansky's sighting would become known

The word of Jansky's finding got out. He assured the public that it was not aliens seeking

But that's just about all anyone could say... for over three decades.

Becklin is one of those rare researchers whose curiosity and determination push our understanding

It was the 1960's and astronomy, like society, was in a period of ferment. Startling new

observations were being made... and new interpretations were in the air.

Quasars had just been discovered... extremely bright beacons of light from deep space. Were

they coming from the centers of distant galaxies? And what powerful objects were generating

To study an event at the center of a galaxy, you have locate it. Young Becklin first took

aim at our neighboring galaxy, Andromeda.

In ultraviolet light, you can see a dense glow in the middle. Becklin found the point

where the light reaches peak intensity... and marked it as the Center.

From our orientation in space, all of the Andromeda galaxy is in full view.

But our galaxy is a different story. We live inside it, of course. Becklin had to find

a way to see through all the dust and gas that obscure our line of sight into the center.

...and obtained a device that reads infrared light... whose wavelengths are similar to

the distances between particles in a dust cloud, allowing them to move right through.

Becklin began measuring the brightness of the light as it rose to a peak... marking

Pinpointing this site would now allow astronomers to begin probing for details with a new generation

of powerful telescopes... to peer into the bright lights... the forbidden zones... deep

Becklin wasn't the only astronomer interested in the galactic center.

Reinhardt Genzel, and a team based at the Max Planck Institute for Extraterrestrial

Physics in Germany, began a similar campaign in 1990... from the New Technology Telescope

A few years later, in 1993, high atop Hawaii's Mauna Kea volcano...

Eric Becklin and colleagues, including Andrea Ghez, began using the newly christened Keck

Telescope. The American and German groups shared the same goal... to pinpoint the precise

location of Sagittarius A*, and find out what it is.

Because the object is too small to see... at 26,000 light years away... they would study

it by tracking the orbits of stars around it.

Even seeing them would take the sensitivity of Keck's wide aperture; an instrument powerful

enough to detect a single candle flame at the distance of the moon...

Meanwhile, using a similar technique, astronomers had focused the new Hubble Space Telescope

on a different galaxy... a giant elliptical cloud of nearly a billion stars, lying some

They tracked gas whipping around its center, figuring its speed at three million miles

per hour.... which led them to calculate the mass of whatever occupied M87's center...

Their measurement - first-ever of its kind  - pointed to the presence of a black hole...

of truly supermassive proportions.... But it didn't conclusively prove its existence.

Back on Earth, the German and American teams each hoped that the proximity of the Milky

...look through the curtains of swirling gas clouds...

...to conclusively prove, for the first time, the existence of supermassive black holes.

This search was part of a larger effort to unravel the complex terrain of the galactic

center, in search of clues to the origins and evolution of our galaxy.

Recently, using Hubble, astronomers documented vast arcs of gas heated up by ferocious winds

Capturing infrared light, the Spitzer Space Telescope, picked up the pervasive swirling

The Chandra X-ray space observatory recorded high-energy radiation mostly likely given

off by ultra-dense neutron stars and small black holes.

Based on Chandra data, scientists estimate that a swarm of 20,000 black holes inhabits

the inner three light years of the galactic center.

If there is a supermassive black hole in the center of it all, the teams would have to

show that it's confined to a very small volume... and that it has enough gravity to whip the

The light of these stars travels 26,000 light years to reach us, only to be blurred in the

last few miles as it hits the Earth's atmosphere. So both teams turned to a method designed

The idea is to snap thousands of pictures in a short time. Because the atmosphere is

in motion, a star's apparent position may shift from image to image. To hone in on the

star's true location, a computer averages the positions, and looks for correlations

Here are the stars they began tracking... clustered around the center of the galaxy.

The first few years' data allowed the teams to calculate the speeds of the stars... and

their rough trajectories around the center.

That allowed them to pinpoint the position of their target...

...as well as its gravitational pull. And that gave them its mass: roughly 3 million

Because no other single object is known to weigh that much, it's strong evidence of a

These data, for example, don't rule out a dense concentration of stars packed into the

center... held there by their mutual gravity.

The proof the teams sought would have to wait for an extraordinary event.