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为什么我们还没有黑洞的照片? – 译学馆
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为什么我们还没有黑洞的照片?

Why Don’t We Have a Photo of a Black Hole Yet?

在2017年 科学家正式开始了一项
In 2017, scientists officially began
雄心勃勃的实验 首次拍摄一个黑洞的照片
an ambitious experiment to photograph a black hole for the first time.
贯穿四个不同大陆的无线电天线网络
A network of radio dishes across four different continents
组成了一个巨大的
joined together to form a giant,
行星大小的天文台 被称作
planet-sized observatory, known as
事件视界望远镜(EHT)
Event Horizon Telescope
它的观测目标有两个
It set its sights on two targets:
在我们银河系中心的特大质量黑洞 人马座A*
Sagittarius A star, the supermassive black hole in the heart
以及潜藏在M-87星系的一个更大的黑洞
of our Milky Way, and an even bigger one lurking in Messier 87.
这个地球大小的望远镜
With a globe sized telescope,
EHT应该有足够的分辨率来直接观测
the EHT should have enough resolution to directly observe
黑洞的事件视界的阴影
the shadow of a black hole’s event horizon.
那么一年多了 照片又在哪里呢
It’s been over a year, so where’s thephoto?
为了找到答案 我们来到了麻省理工大学的海斯塔克天文台
To get some answers, we went to MIT Haystack Observatory,
有两个观测枢纽负责处理
one of the two hubs responsible
所有的观测数据 它是其中之一
for processing all of the observing data.
很多人都想知道 为什么到现在你们还没发布照片呢
A lot of people wonder, why haven’t you released an image yet?
原因有三个
There are three reasons for that.
一是数据传输到这里需要花费很长时间
One is that it took a long time for the data to get here.
每台望远镜
At each telescope,
我们每秒要记录64GB的数据
we record 64 gigabits per second of data.
我们要记录一整晚的数据
We record throughoutthe course of a night.
所以我们讨论的是数以“拍字节”的数据
So we’re talking about several petabytes ofdata.
而对于我们谈论到的数据量
For the data volumes we’re talking about,
用网络来传递这些数据是远远不够的
the Internet is insufficient to transport for the data.
没有什么比用飞机运输硬盘更快的了
Nothing beats loading up hard drives onto an airplane and shipping them.
将那些来自于智利和南极的望远镜的硬盘
And shipping hard drives from telescopes in Chile and the South Pole
运到数据处理器 只需几个月的时间
to data correlators just took months.
第二个原因是在校准上我们一直十分严谨
The second reason is because we’re being very careful on the calibration.
在数据运输到海斯塔克后
After the data were shipped to Haystack,
这里的团队就开始关联这些数据
the team here started to correlate the data.
一旦它们被整合在一起
Once the data were correlated,
我们会将它们移交给校准和误差分析团队
we handed them off to the calibration and error analysis team
去寻找条纹
to find fringes.
这是我们第一次
For the first time,
将所有的基准线进行极其灵敏的检测
we had incredibly sensitive detections on all of our baselines.
这意味着我们开始能分辨出
And that means that we could actually start
所有设备本身的细微碰撞
to see all the little bumps and wiggles that
和摇摆 而非信号源产生的信号
were instrumental in nature rather than fromthe source.
我可以举几个例子
I can show some example here:
比如我们其中的一个观测目标 人马座A
one of our target, the Sagittarius A star.
所有的物体都在高速旋转 30分钟转一圈
Everything is rotating around 30 minutes,which is really fast.
事件视界望远镜
The Event Horizon Telescope
被设计成能够在非常小的时间刻度里捕捉到正在发生的事情
is designed to actually catch things happeningon very short timescales.
但它需要要花很长时间来检测发生了什么
It takes a lot of time to check what’s happening.
例如 仪器自身的影响是多少
For example, what’s the instrumentation effect?
实际的轻微影响 或者副作用又是多少
What’s the actual minor effect, or side effect?
第三个原因就是我们格外的谨慎
And the third reason is we’re just being extra careful.
我们时刻都在进行内部数据复查
We have internal reviews all the time.
一个团队先开始处理这些数据
Where one team goes ahead and works with the data.
之后 其他没有参与其中的人
And then people who weren’t involved in that
可以去看他们的结果
can look at the results and say,
问他们“你们想过这些吗?
“Alright, what did you think about this?
你们尝试过这个方案吗?”
Did you try this?”
而且在项目的这个阶段
At this stage of the project,
团队拥有足够可靠的数据集
the team has a solid enough data set
来开始整合这些图像
to start putting together images.
望远镜本身
The telescope coverage itself
并没有覆盖整个星球
doesn’t cover all of the planet.
所以实际上当我们想制作图像时
So, when we actually want to make images,
存在着无数种可能的图像
there is an infinite number of possible images
可以匹配观测的数据集
can fit our data set.
我们需要真正找出这些数据源最可能的图像
And we need to actually find what is the most likely images for these sources.
这好比是一份侦探工作
It’s like a detective work.
其实我们有4组不同的团队来制作图像
We actually have four different teams of people making images.
他们都在摸索着工作
And they’re working blindly.
这组做一张图 那组做一张图
So one team makes an image,a second team makes an image.
到最后对比这些图像并看看它们是否一致
And then at the end we compare them and say, are these consistent?
然而这又带出一系列新的阻碍
But that comes with a whole new set of obstacles.
在制作我们银河系的黑洞 人马座A的图像时
For our Milky Way black hole, Sagittarius A star,
我们面临着两个挑战
there are two challenges.
我们想要看到的是它的结构
What we are expecting to see is the structure,
或者说黑洞周围的等离子体流
or the plasma flow around the black hole is
在做动态变化
dynamically changing.
我们本应对这些黑洞进行影像记录
We are supposed to take a movie of these black holes.
但这却给图像重组带来另一些挑战
That pose some challenge for the image reconstruction.
另一个问题是由于人马座A
Another challenge is that because Sagittarius A star is
位于银河的正中心
at the center of our galaxy.
我们是穿过许多银河悬臂对其进行观察
We are looking through the many spiral arms of our galaxy.
这会使得人马座A星的图像略有模糊
That will slightly blur the image of SagittariusA star.
所以同时我们需要减轻那些
So we also need to mitigate a kind of
挡在我们和人马座A之间的星际等离子体
scattering effect from the interstellar plasma
所带来的散射效应
In front of us on the way to Sagittarius A star.
我们再说另外一个星体 M-87
If we move on another source, M-87,
它存在着完全不同的挑战
it also has a completely different challenge.
因为M-87不位于我们的银河系
Because M-87 is not in our galaxy,
所以有一些不确定性
there are someuncertainties.
在解释这些是什么之前
Before we explain what those are,
要知道制作一个黑洞照片时
remember when it comes to imaging a black hole,
科学家们无法直接观测
scientists can’t observe it directly.
他们是在观察黑洞的事件视界附近
They’re looking at the surrounding matter and light
被引力所吸引的周围的物质与光线
that’s being pulled by gravity around the black hole’s event horizon.
你可能以前听说黑洞事件视界这个词
You’ve likely heard that phrase before,
它是一个终极边界 在那之内
It’s the ultimate boundary the place where
任何事物 甚至光都无法逃脱
“Nothing, not even light can escape.”
任何事物甚至光都无法逃脱它们的引力场
“Nothing, not even light can escape theirgravitational pull.”
黑洞是一种质量超大的星体
“The black hole is a star so massive
其引力使得光都无法逃脱
that not even light can escape from it.”
这个经典说法之下存在一个几何参数
Underneath that classic saying is a geometric parameter that underpins
它对EHT在时空中定位黑洞十分重要
how the EHT maps black holes in space time.
这个参数称为史瓦西半径
It’s called the Schwarzschild radius.
1916年 德国天体物理学家卡尔·史瓦西
Back in 1916, German astrophysicistKarl Schwarzschild was inspired
受爱因斯坦相对论的启发
by Einstein’s theory of relativity,
在他作为一名士兵参与一战的闲暇之余
and in his free time fighting as a soldier in World War I,
他得出了计算黑洞半径的公式
he came up with this formula to calculate the radius of a black hole:
其中 M为黑洞质量
Where M is the mass,
G是万有引力常数
G is the universal constant of gravitation,
c则是光速
and c is the speed of light.
史瓦西半径是黑洞中心
The Schwarzschild radius is the distance
到事件视界上的点的距离
from the center of the black hole to the event horizon,
光也无法逃脱到那些点之外
that point where light can’t escape.
这个模型适用于不旋转的黑洞
This model works for non-rotating black holes.
但这个领域在史瓦西之后得到了发展
But the field has advanced since Schwarzschild,
克尔度规将黑洞旋转纳入考量
with the Kerr metric, which takes black hole spin into account.
从根本上说 史瓦西半径是黑洞观测的关键
Ultimately, the Schwarzschild radius is key,
因为它帮助物理学家得出黑洞尺寸
because it helps physicist unlock the size of a black hole,
这在你尝试建立图像时非常重要
which is pretty important if you’re trying tocreate an image.
黑洞的显示尺寸取决于
Apparent size of the black hole is determined by
我们到M-87的距离 或者黑洞有多远
distance to M-87 and how far the black hole is
以及黑洞的质量大小
and how heavy the black hole is.
由于黑洞的尺寸
Because the size of black hole is proportional to
与黑洞的质量是成比例的
the mass of the black hole.
我们对于距离的测量非常准确
We have a very good measurement for the distance,
但是对于M-87的质量
but still there is a factor of two uncertainties
依然有一个因素存在两点不确定性
for the mass of M-87.
黑洞阴影的大小由黑洞本身质量决定
The size of the shadow is determined by the black hole’s mass.
质量越大 阴影越大
The bigger the mass, the larger the shadow.
但如果质量是个问号
But if the mass is a question mark,
那么就有麻烦了
that could pose a challenge.
如果我们无法得出阴影面积
If we can not get the shadow,
那么可能意味着我们目前测量很多星系中
may be suggesting that the current way to measure the mass of
超大质量黑洞的质量的方法
the supermassive black hole in many galaxies
可能存在某种错误 需要我们进一步校准
could be somewhat wrong and we need to do recalibration.
在团队仍在处理图像时
While the teams are still working on images,
他们对最终的结果会是如何 做出了一些猜想
they have some guesses as to what the finals might look like.
对于人马座A星 预期的图像不同于之前的一些
For Sagittarius A star, the expected image is very different from,
比如 星际穿越中的那副著名图像
for instance, the famous image of”Interstellar.”
我们会看到它是像新月一样的图案
We will see it’s like a crescent image;
一侧更明亮一些 有一片阴影
one side is brighter and there is a shadow and
另一侧则十分昏暗
the other side is very faint.
对于M-87 我们预期
For M-87, we are expected to see
同时观测到落入黑洞的吸积流与
both accretion flow falling into the black hole and also
逃离黑洞的等离子体形成的喷流
the jet, which is the plasma flow escaping from the black hole.
这些图像仍是初步的结果
Those images are still preliminary,
它们还没有被正式发布
and they haven’t been released yet,
但我们预计在今年冬季末或者19年春天
but we expect to have a release of the papers and the images
向外界发布一些论文和图像
in the late winter or early spring of 2019.
黑洞是我们宇宙的基础组成部分
Black holes are basic constituents of our universe,
这些庞然大物几乎是
and these monsters are the anchor points
每个星系的锚定点
in virtually every galaxy.
对它们的形成和动力学的研究
Understanding their formation and dynamics could
会是对爱因斯坦相对论的最终考验
be the ultimate test of Einstein’s theory of relativity,
相对论有两个重要推论:
which makes two key predictions.
首先 黑洞的引力
First that the gravity of a black hole
能够弯曲时空并将一切物质吸向它
curves space time and draws everything towards it.
第二是
And secondly that the shadow
吸积盘投射出的事件视界的阴影
of the event horizon cast by the accretion disk
极可能是圆形的
should be mostly circular.
根据最后得出图像的模样
Depending on what the final image looks like,
我们可能需要修正宇宙法则
we might need to update the law of the cosmos.
每个人都认为有东西
Everyone believes something is
落入黑洞并且有东西逃出来
falling down the black hole and something is escaping black hole,
但我们依旧没有任何图像
but we still don’t have anyimages.
现在我们处于一个激动人心的时刻
We are now in a very exciting moment
我们将能够验证那些人们一百多年前
that we can actually test what people thought about
提出的东西
a hundred years ago.
我认为爱因斯坦可能是正确的
My take is that Einstein was probably right.
每次我们尝试去验证相对论 相对论都通过了考验
Every time we’ve tried to test relativity,relativity passes the test.
黑洞图像可能改变我们对相对论认知
the image of the black hole could change our conception of relativity,
或者证明它是对的
or it could confirm it.
所以你可以设想会看到一个圆形的阴影
So you predict that you will see a circular shadow,
并且阴影的尺寸是可以通过
and the size of that shadow is predictable
黑洞的距离和黑洞的质量预测的
from the distance to the source and the mass of the black hole.
我们也可能不走运 根本无法看到它
We could always get unlucky and not see a shadow at all.
但我认为这些原始数据
But I think that the preliminary data tells us
告诉了我们还是有些东西可以被观测到
us there’s something there to be seen.
想要了解更多的纪录片 请点击这里
For more science documentaries, check outthis one right here.
不要忘了订阅 请到Seeker浏览更多视频
Don’t forget to subscribe, and keep coming back to Seeker for more videos.

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黑洞的观测工作已经开始了一年了,那么现在照片的制作怎么样了呢?

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