This is the basic question of somebody who's interested

如何观察那些你看不见的东西？

in finding and studying black holes.

对于那些有兴趣寻找和研究黑洞的人来讲

Because black holes are objects

这是一个很基本的问题

whose pull of gravity is so intense

因为黑洞的引力

that nothing can escape it, not even light,

太大了

so you can't see it directly.

任何物体，甚至光都无法逃脱

So, my story today about black holes

所以你用肉眼根本看不见它。

is about one particular black hole.

我今天所要说的黑洞

I'm interested in finding whether or not

非常特殊。

there is a really massive, what we like to call

我很想知道

"supermassive" black hole at the center of our galaxy.

在我们这个星系是否存在一个巨大的

And the reason this is interesting is that

我们称之为“特大”的黑洞½

it gives us an opportunity to prove

有意思的是

whether or not these exotic objects really exist.

这让我们有机会去证实

And second, it gives us the opportunity

这些奇异的东西是否真正地存在。

to understand how these supermassive black holes

再有这也为我们

interact with their environment,

了解这些特大质量的黑洞

and to understand how they affect the formation and evolution

如何与它们周围环境相互作用

of the galaxies which they reside in.

以及了解它们如何影响

So, to begin with,

它们所处星系的形成和演化提供了很好的机会。

we need to understand what a black hole is

那么，首先

so we can understand the proof of a black hole.

我们需要了解什么是黑洞

So, what is a black hole?

这样，我们才能找出黑洞存在的证据。

Well, in many ways a black hole is an incredibly simple object,

那么，何为黑洞？

because there are only three characteristics that you can describe:

呃，从很多方面上讲，黑洞是一个相当简单的物体

the mass,

因为只需三个特征就可以概括它：™

the spin, and the charge.

质量

And I'm going to only talk about the mass.

旋转和电荷

So, in that sense, it's a very simple object.

今天，我只讲它的质量。

But in another sense, it's an incredibly complicated object

从这个角度上来说，黑洞就简单了。

that we need relatively exotic physics to describe,

但从另外一个角度来讲，它又是相当的复杂

and in some sense represents the breakdown of our physical understanding

复杂到要用很奇特的物理学来描述它，

of the universe.

但这又在某种程度上说明了我们对宇宙的物理认识

But today, the way I want you to understand a black hole,

很是有限。

for the proof of a black hole,

但是，今天，我想让大家这样理解黑洞

is to think of it as an object

因为我们要证明它的存在，

whose mass is confined to zero volume.

我门把它当作某个物体来看，

So, despite the fact that I'm going to talk to you about

但是却没有体积。

an object that's supermassive,

所以现在我向大家介绍的是

and I'm going to get to what that really means in a moment,

质量特别大，

it has no finite size.

但是确切说又像是某个瞬间，

So, this is a little tricky.

因为它没有具体的大小。

But fortunately there is a finite size that you can see,

现在看来些滑稽了。

and that's known as the Schwarzschild radius.

幸运的是，我们还有具体的大小可供参照的，

And that's named after the guy who recognized

那就是施瓦西半径。

why it was such an important radius.

这是以发现

This is a virtual radius, not reality; the black hole has no size.

这个半径的重要性的人来命名的。

So why is it so important?

这并不是黑洞的实际半径，因为黑洞并无大小。

It's important because it tells us

那为什么它如此重要

that any object can become a black hole.

它的重要之处在于告诉我们

That means you, your neighbor, your cellphone,

任何物体都可以变成黑洞。

the auditorium can become a black hole

也就是说你， 你的邻居，还有你的手机，

if you can figure out how to compress it down

甚至这个听众席，都可能变成黑洞，

to the size of the Schwarzschild radius.

只要你能发现把物体压缩到

At that point, what's going to happen?

施瓦西半径的大小。

At that point gravity wins.

如果可以的话，很发生什么呢？

Gravity wins over all other known forces.

此时，引力战胜了一切。

And the object is forced to continue to collapse

引力战胜了我们所知的其他所有的力量。

to an infinitely small object.

而物体本身也必须继续压缩

And then it's a black hole.

直至变得无限小。

So, if I were to compress the Earth down to the size of a sugar cube,

这时黑洞就形成了。

it would become a black hole,

所以如果我把地球压缩到方糖般大小

because the size of a sugar cube is its Schwarzschild radius.

它就变成黑洞了，

Now, the key here is to figure out what that Schwarzschild radius is.

因为方糖的大小就是地球的施瓦西半径的大小。

And it turns out that it's actually pretty simple to figure out.

现在，关键就是要解决施瓦西半径到底是多大了。

It depends only on the mass of the object.

其实在也很简单。

Bigger objects have bigger Schwarzschild radii.

该半径取决于物体的质量。

Smaller objects have smaller Schwarzschild radii.

物体大施瓦西半径就大

So, if I were to take the sun

物体小相应地该半径也就小。

and compress it down to the scale of the University of Oxford,

所以，如果我把太阳

it would become a black hole.

压缩到和牛津大学一样大，

So, now we know what a Schwarzschild radius is.

那么太阳就变成黑洞了。

And it's actually quite a useful concept,

现在我们知道施瓦西半径是什么了。

because it tells us not only

了解这个很重要，

when a black hole will form,

它不仅告诉我们

but it also gives us the key elements for the proof of a black hole.

何时形成黑洞，

I only need two things.

同时也告诉我们找寻黑洞存在依据的关键

I need to understand the mass of the object

我只要知道两件事。

I'm claiming is a black hole,

我需要知道物体的质量，

and what its Schwarzschild radius is.

我要把它变为黑洞，

And since the mass determines the Schwarzschild radius,

还有它的施瓦西半径。

there is actually only one thing I really need to know.

因为物体的质量决定了它的施瓦西半径，

So, my job in convincing you

所以实际上我只需要一件事。

that there is a black hole

所以，我要你们相信

is to show that there is some object

黑洞的存在

that's confined to within its Schwarzschild radius.

就只要提供一个

And your job today is to be skeptical.

被压缩到施瓦西半径的物体就可以了。

Okay, so, I'm going to talk about no ordinary black hole;

而你们就今天就先保持自己的怀疑态度吧。

I'm going to talk about supermassive black holes.

好，接下来我要讲的绝不是普通的黑洞；

So, I wanted to say a few words about what an ordinary black hole is,

我将要介绍的是超质量的黑洞

as if there could be such a thing as an ordinary black hole.

在此，我先说说什么是普通的黑洞，

An ordinary black hole is thought to be the end state

我们先假定存在这样的黑洞。

of a really massive star's life.

普通黑洞被认为是

So, if a star starts its life off

大恒星生命的终了状态。

with much more mass than the mass of the Sun,

因此，当一个恒星消亡

it's going to end its life by exploding

而这个恒星的质量又远大于太阳，

and leaving behind these beautiful supernova remnants that we see here.

它将以爆炸结束生命

And inside that supernova remnant

并留下我们见的那些漂亮的超新星残骸

is going to be a little black hole

在这些残骸之中

that has a mass roughly three times the mass of the Sun.

就会有个小黑洞

On an astronomical scale

它的质量大约是太阳质量的三倍。

that's a very small black hole.

从天文学来看

Now, what I want to talk about are the supermassive black holes.

这个黑洞算是小的了。

And the supermassive black holes are thought to reside at the center of galaxies.

下面我要讲的是特大黑洞了。

And this beautiful picture taken with the Hubble Space Telescope

据说这些黑洞存在于星系的中心位置。

shows you that galaxies come in all shapes and sizes.

这张图片是哈勃望远镜拍下的，

There are big ones. There are little ones.

我们可以看到各种形状大小的星系。

Almost every object in that picture there is a galaxy.

有大的，也有小的。

And there is a very nice spiral up in the upper left.

这里面几乎每个可见物体都是星系。

And there are a hundred billion stars in that galaxy,

看在左上角有个螺旋形

just to give you a sense of scale.

在那个星系里有一千亿的星星，

And all the light that we see from a typical galaxy,

让大家有个大小的意识。

which is the kind of galaxies that we're seeing here,

在某个星系我们见的光，

comes from the light from the stars.

就是我们现在看的这些星系，

So, we see the galaxy because of the star light.

是来自恒星的光。

Now, there are a few relatively exotic galaxies.

我们之所以能看见星系全是靠这些星星的光。

I like to call these the prima donna of the galaxy world,

在这其中有不少相对来说奇怪的星系。

because they are kind of show offs.

我习惯称它们为歌剧女王，

And we call them active galactic nuclei.

因为它们太能显摆了。

And we call them that because their nucleus,

我们叫它们活跃星系核子。

or their center, are very active.

因为它们的核子活跃异常，

So, at the center there, that's actually where

还有中心位置处。

most of the starlight comes out from.

所以在中间那块

And yet, what we actually see is light

大部分星光都是从那发出的

that can't be explained by the starlight.

但是我们看见的只能说是光

It's way more energetic.

不能说是星光。

In fact, in a few examples it's like the ones that we're seeing here.

因为这比星光更活跃。

There are also jets emanating out from the center.

下面例子中跟我们现在看的这些有些相似。

Again, a source of energy that's very difficult to explain

这些都是从中间发出来的。

if you just think that galaxies are composed of stars.

如果大家把星系认为是由星星组成的，

So, what people have thought is that perhaps

那这股能量就很难解释了。

there are supermassive black holes

人们原来想

which matter is falling on to.

或许是有特大的黑洞

So, you can't see the black hole itself,

物质才被吸引过去的。

but you can convert the gravitational energy of the black hole

我们看不见黑洞本身

into the light we see.

但是我们却可以把它的这种引力

So, there is the thought that maybe supermassive black holes

转换为我们所见的光来思考

exist at the center of galaxies.

所以有这么一种想法就是特大黑洞或许

But it's a kind of indirect argument.

存在于星系的中心处。

Nonetheless, it's given rise to the notion

但这仅是提供了一种间接论据

that maybe it's not just these prima donnas

但是，这却让我们有了这样一种想法

that have these supermassive black holes,

或许不仅是这些歌剧女王

but rather all galaxies might harbor these

有特大黑洞

supermassive black holes at their centers.

可能所有的星系

And if that's the case -- and this is an example of a normal galaxy;

在中心位置处都有特大黑洞

what we see is the star light.

假如这样的话--这就是个普通的星系；

And if there is a supermassive black hole,

我们看见的是星光

what we need to assume is that it's a black hole on a diet.

假设存在这样的特大黑洞

Because that is the way to suppress the energetic phenomena that we see

那么这个黑洞肯定是在节食

in active galactic nuclei.

因为这才能解释为什么在其它活跃星系核子的那股能量

If we're going to look for these stealth black holes

在这却被压制住了。

at the center of galaxies,

如果我们想要在星系中心找寻

the best place to look is in our own galaxy, our Milky Way.

这些隐藏的黑洞

And this is a wide field picture

那么最好的地方就是在我们银河系寻找了。

taken of the center of the Milky Way.

这张图片

And what we see is a line of stars.

是银河系中心的大范围图片

And that is because we live in a galaxy which has

我们可以看到星星排成的列队

a flattened, disk-like structure.

因为我们这个星系

And we live in the middle of it, so when we look towards the center,

结构像扁平的磁盘形状

we see this plane which defines the plane of the galaxy,

我们处在银河系的中心，所以如果我们看它的中心

or line that defines the plane of the galaxy.

我们把这个平面看成是银河的平面

Now, the advantage of studying our own galaxy

或者把这条线看成是银河平面

is it's simply the closest example of the center of a galaxy

研究我们自己星系的好处呢

that we're ever going to have, because the next closest galaxy

就是这是我们能找的星系中心最近的例子了

is 100 times further away.

因为离我们再近点的星系

So, we can see far more detail in our galaxy

是我们离银河系中心100倍的距离之外了

than anyplace else.

因而在我们这个星系我们可以把细节看的更清楚

And as you'll see in a moment, the ability to see detail

在其它地方就不行了

is key to this experiment.

一会大家就知道了，能够观察到细节

So, how do astronomers prove that there is a lot of mass

是实验的关键

inside a small volume?

那么天文学家怎样证明

Which is the job that I have to show you today.

体积小质量大的物质呢

And the tool that we use is to watch the way

今天我得给大家展示一下了

stars orbit the black hole.

我们要用的工具就是观察

Stars will orbit the black hole

这些星星是怎样绕黑洞运行的

in the very same way that planets orbit the sun.

星星绕黑洞的运行轨迹

It's the gravitational pull

跟行星绕太阳的轨迹差不多

that makes these things orbit.

是引力

If there were no massive objects these things would go flying off,

使得物体按轨道运行的

or at least go at a much slower rate

如果是没有中间的大物体这些物体肯定就飞脱出去了

because all that determines how they go around

至少是运行速度更慢

is how much mass is inside its orbit.

因为决定它们运行轨迹的是

So, this is great, because remember my job is to show

轨道内含的质量大小

there is a lot of mass inside a small volume.

这下好了，记得吧我的任务就是说明

So, if I know how fast it goes around, I know the mass.

体积小质量大的情况吧

And if I know the scale of the orbit I know the radius.

如果我知道物体的运行速度，我就可以知道它的质量了

So, I want to see the stars

还有如果我知道轨道大小就等于知道了轨道半径

that are as close to the center of the galaxy as possible.

现在我想看看那些

Because I want to show there is a mass inside as small a region as possible.

离星系中心越近越好的星星

So, this means that I want to see a lot of detail.

因为我想在尽小的区域内演示大质量

And that's the reason that for this experiment we've used

也就是说我想尽可能地看清楚些

the world's largest telescope.

这就是为什么这次实验我们要用

This is the Keck observatory. It hosts two telescopes

世界上最大的望远镜了

with a mirror 10 meters, which is roughly

这是凯克实验室，里面有两台望远镜

the diameter of a tennis court.

镜片有10米，这大约相当于

Now, this is wonderful,

一个网球场的宽了

because the campaign promise

这下好极了

of large telescopes is that is that the bigger the telescope,

因为我们说过

the smaller the detail that we can see.

望远镜越大

But it turns out these telescopes, or any telescope on the ground

我们就越能看到细节

has had a little bit of a challenge living up to this campaign promise.

但结果是这些望远镜，或是说所有的望远镜

And that is because of the atmosphere.

要达到我们的要求还是要战胜一点小困难

Atmosphere is great for us; it allows us

这就是我们的大气层了

to survive here on Earth.

大气对我们是有好处的；它使得我们

But it's relatively challenging for astronomers

可以在地球上生存

who want to look through the atmosphere to astronomical sources.

这对天文学家们要想

So, to give you a sense of what this is like,

透过大气层看到观察物是有些挑战性的

it's actually like looking at a pebble

说的更形象一点

at the bottom of a stream.

这就像看水底的

Looking at the pebble on the bottom of the stream,

小鹅卵石

the stream is continuously moving and turbulent,

我们要看河底的鹅卵石

and that makes it very difficult to see the pebble on the bottom of the stream.

可是水流还是在不停地流动翻滚

Very much in the same way, it's very difficult

这要看清水底的鹅卵石就不容易了

to see astronomical sources, because of the

同样情况下

atmosphere that's continuously moving by.

我们要看清观测物

So, I've spent a lot of my career working on ways

可是大气却在不停地动着，这就有难度了

to correct for the atmosphere, to give us a cleaner view.

所以我的大部分工作时间都用在了

And that buys us about a factor of 20.

改造大气层以便可以清晰观察上。

And I think all of you can agree that if you can

这就很难了

figure out how to improve life by a factor of 20,

我想大家都会相信

you've probably improved your lifestyle by a lot,

如果我们可以用®©来改善生活的话

say your salary, you'd notice, or your kids, you'd notice.

估计我们早想出很多其它的方法了

And this animation here shows you one example of

比如您的薪水，或是孩子

the techniques that we use, called adaptive optics.

这个动画实际上是我们

You're seeing an animation that goes between

所用的一种技术，叫做自适应光学

an example of what you would see if you don't use this technique --

从这个动画中我们可以看出

in other words, just a picture that shows the stars --

如果不用这种技术我们能看到的