black hole. That's when the Event Horizon Telescope will be releasing their

黑洞的照片 因為屆時事件視界望遠鏡將會發布

results and I haven't seen them yet but I think they're going to look something

他們的結果 我還沒有見過它們但是我認為他們看起來應該

like this and I can be relatively confident because well it's gonna look a

就像這樣 我可以比較自信地說它看起來有點像是

bit like a fuzzy coffee mug stain. But if you are disappointed by this image I

一團模糊的咖啡漬 但如果你對此覺得失望你很有可能

think that misses the gravity of the situation. From this image we should be

錯失了這個事件的莊重性 從這個圖像中我們應該可以

able to tell whether the general theory of relativity accurately predicts what

由廣義相對論準確地預測出在黑洞周圍

happens in the strong gravity regime that is what happens around a black hole

在強大的重力場中會發生什么

what I want to do here is understand what exactly we are seeing in this image

我想做的是來理解我們到底在這個圖像中看見了什么

so here is my mock black hole of science and this sphere represents the event

所以我準備了一個“黑洞” 這個球體表示

horizon. That is the location from which not even light fired radially away from

事件視界 那是連黑洞所放射出的光都無法

the black hole could be detected by an outside observer. All of the world lines

被外部觀測者探測到的區域 所有的世界線

end up in the center of the black hole in the singularity once you're inside

終結于黑洞中心的奇點 只要你進入其中

here there is no coming back not even for light. The radius of the

就再也不能回來 即便是光也一樣 事件視界

event horizon is known as the Schwarzschild radius. Now if we were just

的半徑以“史瓦西半徑”為人所熟知 現在如果我們

to look at a black hole with nothing around it we would not be able to make

去看一個周圍什么都沒有的黑洞 我們會沒有辦法

an image like this because well it would just absorb all electromagnetic

看到一張像這樣的圖像 因為它會吸收所有落到它上面的

radiation that falls on it but the black hole that they're looking at

電磁波 但是他們(望遠鏡)正在觀測的是

specifically the one in the center of our Milky Way galaxy, Sagittarius A*

我們銀河系中心的“人馬座A*”

has matter around it in an accretion disk. In this accretion disk there is

在它周圍有物質環繞 也就是吸積盤 在吸積盤里面有

dust and gas swirling around here very chaotically it's incredibly hot we're

塵埃于氣體在混亂地旋轉 它非常的熱——

talking to millions of degrees and it's going really fast a significant fraction

有上百萬度 同時又非常的快 是光速的幾分之一

of the speed of light and it's this matter that the black hole feeds off and

這些物質被黑洞吸收

gets bigger and bigger over time but you'll notice that the accretion disk

然后變得越來越大 你可能會注意到吸積盤

does not extend all the way in to the event horizon. Why is that? Well that's

并沒有擴展到事件視界 為什么？

because there is an inner most stable circular orbit and for matter around a

因為有一個最內部穩定圓形軌道 對于一個不旋轉的黑洞

non-spinning black hole that orbit is at three Schwarzschild

周圍的物質來說 軌道的半徑大概是

radii now in all likelihood the black hole at the center of our galaxy will be

三倍史瓦西半徑 我知道我們銀河系中心的黑洞應該

spinning but for simplicity I'm just considering the non spinning case. You

會是旋轉的 但是為了簡單一點 我只考慮不旋轉的情況

can see my video on spinning black holes if you want to find out more about

如果你想了解更多 可以去看我的關于旋轉的黑洞的視頻

that. So this is the innermost orbit for matter going around the black hole if it

再回到這個最內部穩定圓形軌道 對于黑洞周圍的物質來說

goes inside this orbit it very quickly goes into the center of the black hole

如果它進到這個軌道的內部 它將會被以極快的速度吸入黑洞

and we never hear from it again but there is something that can orbit closer

然后我們就再也看不見它了 但是還有一些東西可以有

to the black hole and that is light because light has no mass it can

離黑洞更近一些的軌道 那就是光 因為光沒有質量

actually orbit at 1.5 Schwarzschild radii. Now here i'm representing it with a ring

它可以以1.5倍史瓦西半徑環繞黑洞 這里我把它表現為一個環

but really this could be in any orientation so it's a sphere of photon

但其實它可以是在任何一個方向 所以它是一個光子軌道組成的球體

orbits and if you were standing there of course you could never go there but if

如果你站在那里——當然你不可能去到那里

you could you could look forward and actually see the back of your head

但如果你可以 你將會看到自己的后腦勺

because the photons could go around and complete that orbit. Now the photon

因為光子可以環繞一圈完成一個軌道

sphere is an unstable orbit meaning eventually either the photons have to

光子球體是不穩定的軌道 意味著光子最終將會

spiral into the singularity or spiral out and head off to infinity now the

旋轉飛入奇點 或者進入無限的宇宙

question I want to answer is what does this black quote-unquote shadow in the

現在我想回答一個問題 這個圖像中心的

image correspond to in this picture of what's actually going on around the

黑黑的影子 到底黑洞周圍在發生什么

black hole. Is it the event horizon? Are we simply looking at this? or is it the

這個黑影是事件視界嗎？ 我們就這么看到它了？ 或者它是光子球？

photon sphere? or the inner most stable circular orbit? Well things are

或者是最內部穩定圓形軌道？ 好吧

complicated and the reason is this black hole warps space-time around it which

這東西很復雜 原因是黑洞扭曲了它周圍的時空

changes the path of light rays so they don't just go in straight lines like we

改變了光線的路徑 所以它們不再像是我們平常想象的那樣

normally imagine that they do I mean they are going in straight lines but

直線傳播 我的意思是它們仍然直線傳播但是

space-time is curved so yeah they go in curves so the best way to think of this

時空被彎曲了所以它們也彎曲了 最好的思考它的方式

is maybe to imagine parallel light rays coming in from the observer and striking

也許是想象觀測者發出的平行光線 射入這個圖形 51

this geometry here. Of course if the parallel light rays cross the event

當然 如果平行光線穿過事件視界

horizon we'll never see them again so they're gone that will definitely be a

*我們并沒有真的發送光線 但是這樣可以幫助理解* *因為來和去的路線是一樣的*

dark region but if a light ray comes in just above the event

我們就看不到了 它們消失了 所以這里肯定會有一個

Rison it too will get bent and end up crossing the event horizon it ends up in

黑暗的區域 但是如果光線從稍微高于

the black hole. Even a light ray coming in the same distance away as the photon

事件視界的位置射入 它會被彎曲 最終進入事件視界 消失在黑洞里

sphere will end up getting warped into the black hole and curving across the

即使光線從和光子球體相同的距離射入

event horizon so in order for you to get a parallel ray which does not end up in

一樣會被彎向黑洞 最終進入事件視界

the black hole you actually have to go out 2.6 radii away if a light ray comes

所以為了使平行光線不被黑洞吸入

in 2.6 Schwarzschild radii away it will just graze the photon sphere at its

你得離黑洞2.6倍史瓦西半徑遠 如果一條光線

closest approach and then it will go off to infinity and so the resulting shadow

以2.6倍史瓦西半徑的距離射入 它將會以最近的距離掠過光子球體

that we get looks like this it is 2.6 times bigger than the event horizon. You

然后它就離開 進入無限的宇宙空間 所以產生的影子

say what are we really looking at here? what is this shadow? well in the center

在我們看來就是2.6倍的事件視界

of it is the event horizon. It maps pretty cleanly onto onto the center of

那我們到底在看什么呢？ 這個影子是什么？ 那么在它的中間

this shadow but if you think about it light rays going above or below also end

是事件視界 它完美地落在這片影子的中心

up crossing the event horizon just on the backside. So in fact what we get is

但是你想想 從上方或下方來的光線同樣會

the whole back side of the event horizon mapped onto a ring on this shadow. So

在另一側進入事件視界 所以事實上

looking from our one point in space at the black hole we actually get to see

事件視界的另一側會完整地對應到這個影子中的一個環

the entirety of the black hole's event horizon. I mean maybe it's silly to talk

所以我們從一個點看黑洞 我們其實可以看見

about seeing it because it's completely black but that really is where the

完整的黑洞的事件視界 我知道

points would map to on this shadow. It gets weirder than that

說“看見”聽起來有點傻因為它完全是黑的 但那確實是

because the light can come in and go around the back and say get absorbed in

那些位置對應在影子上 還有更奇怪的

the front you get another image of the entire horizon next to that and another

因為光線可以射入 然后轉一圈 再被吸收

annular ring and then another one after that and another one after that and you

所以你可以在下一個環“看見”又一個完整的事件視界

get basically infinite images of the event horizon as you approach the edge

然后又是一個 之后再一個 還是一個 所以當你

of this shadow. So what is the first light that we can see? It is those light

接近這片影子的邊緣的時候 基本上可以獲得無限多的事件視界的圖像

rays that come in at just such an angle that they graze the photon sphere and

所以我們可以看見的最初的光線是？ 是那些從某個角度射入

then end up at our telescopes. And they produce a shadow which is 2.6 times the

然后掠過光子球體 最終

size of the event horizon. So this is roughly what we'd see if we happen to be

進入我們的望遠鏡 它們產生了比事件視界大2.6倍

looking perpendicular to the accretion disk but more likely we will be looking

的影子 所以這大致上就是當我們從垂直于吸積盤的角度

at some sort of random angle to the accretion disk. We may be even looking edge-on

觀察黑洞時將會看到的 但是更有可能的是我們將會

And in that case do we see this shadow of the black hole? you might think

以一個隨機的角度觀測 我們甚至可能看著吸積盤的側邊

that we wouldn't but the truth is because of the way the black hole warps

在那種情況下我們可以看見黑洞的影子嗎？ 你也許認為不行

space-time and bends light rays, we actually see the back of the accretion

但事實是由于黑洞扭曲時空

disk the way it works is light rays coming off the accretion disk bend over

并且彎曲光線 實際上我們可以看見吸積盤的后面

the top and end up coming to our telescopes so what we end up seeing is

這事情發生的方式是從吸積盤發出的光線

something that looks like that. Similarly light from the bottom of the

被彎曲穿過頂部 然后進入我們的望遠鏡 所以我們最終可以看見的是

accretion disk comes underneath gets bent underneath the black hole and comes

看起來像這樣的東西 類似的 吸積盤底部的光線也會

towards us like that and this is where we get an image that looks something

從下方穿過 在黑洞下方被彎曲

like the interstellar black hole.

然后朝我們飛來 這樣我們就會得到一張圖像 看起來就像

it gets even crazier than this because light

《星際穿越》里的黑洞

that comes off the top of the accretion disk here can go around the back of the

甚至還要更瘋狂一些 因為

black hole graze the photon sphere and come at the bottom right here producing

從吸積盤頂部發出的光可以從黑洞的背面

a very thin ring underneath the shadow. Similarly light from underneath the

繞過來 掠過光子球體 然后來到底部 就在這里

accretion disk in the front can go underneath and around the back and come

在影子的下方產生一個非常細的環 類似的 從吸積盤下方來的光線

out over the top which is why we see this ring of light here. This is what we

可以從下方繞過黑洞然后

could see if we were very close to the black hole, something that looks truly

從上方出來 這就是為什么這里有個光環 這是

spectacular. One other really important effect to consider is that the matter in

如果我們非常靠近黑洞 我們可以看見的 看起來非常壯觀的場面

this accretion disk is going very fast, close to the speed of light and so if

還有一個要考慮的重要的效應就是吸積盤里的物質

it's coming towards us it's gonna look much brighter than if

運動得非常快 接近光速

it's going away. That's called relativistic beaming or Doppler beaming

所以如果它朝我們的方向運動 它將會比遠離我們的方向看起來亮得多

and so one side of this accretion disk is going to look much brighter than the

這叫做相對性光束或多普勒光束

other and that's why we're gonna see a bright spot in our image. So hopefully

所以吸積盤的一邊將會看起來比另一邊亮得多

this gives you an idea of what we're really looking at when we look at an

所以我們就會在圖像上看見一個亮點

image of a black hole if you have any questions about any of this please leave

希望當你看著一張黑洞的圖像的時候 這個視頻會給你一點關于

them in the comments below and I will likely be making a video for the launch

你在看什么的頭緒 如果你有關于這個的任何疑問

of the first ever image of a black hole so I'll try to answer them then. Until

請在下方留言 我應該會為第一張黑洞照片的發展

then I hope you get as much enjoyment out of this as I have

做一個視頻 到時候我將會解答你們的問題

because this has truly been my obsession for like the last week.

我希望你們和我一樣感受到如此多的樂趣

I guess what

因為這在過去的一周里真的讓我著迷

would be exciting is to watch it over time how it changes, right? there's a lot of

我猜會令人興奮的事情是看著它隨時間變化 對吧？

hope that there are blobs moving around and you know if you see a blob going

很有可能會有一些團塊動來動去然后你可以看見一個團塊

round the front and then it goes around the back but you see it in the back

從前面繞過去 繞到后面 但是你還是可以在

image etc then that's gonna be kind of cool

圖像上看見它 這是很棒的事