How radio telescopes show us unseen galaxies | Natasha Hurley-Walker

Transcriber: Joseph Geni Reviewer: Joanna Pietrulewicz

譯者: Lilian Chiu 審譯者: Wilde Luo

Space, the final frontier.

太空，最後的邊境。

I first heard these words when I was just six years old,

我 6 歲時第一次聽到這句話，

and I was completely inspired.

並因此深受啓發。

I wanted to explore strange new worlds.

我想要去探索新奇的世界。

I wanted to seek out new life.

我要去尋找新的生命。

I wanted to see everything that the universe had to offer.

我想要去見識宇宙的一切。

And those dreams, those words, they took me on a journey,

這些夢想和話語 讓我踏上了這個旅程，

a journey of discovery,

充滿發現的旅程，

through school, through university,

經過中學、經過大學，

to do a PhD and finally to become a professional astronomer.

唸博士、最後成為專業天文學家。

Now, I learned two amazing things,

我學到了兩件很棒的事，

one slightly unfortunate,

第一件稍微有點不幸，

when I was doing my PhD.

當我在唸博士時。

I learned that the reality was

我學到現實是，

I wouldn't be piloting a starship anytime soon.

駕駛太空船不是近期可實現的事。

But I also learned that the universe is strange, wonderful and vast,

但我也學到，宇宙是 奇異、美妙、浩瀚的，

actually too vast to be explored by spaceship.

事實上，它太浩瀚了 太空船也無法探索完。

And so I turned my attention to astronomy, to using telescopes.

因此我把注意力轉向天文學， 轉向使用望遠鏡。

Now, I show you before you an image of the night sky.

我現在呈現在你們眼前的 是夜晚天空的影像。

You might see it anywhere in the world.

你在世界任何地方都可以看到它。

And all of these stars are part of our local galaxy, the Milky Way.

所有這些星星都是 我們這個銀河系的一部份。

Now, if you were to go to a darker part of the sky,

如果你到比較暗的一個地方，

a nice dark site, perhaps in the desert,

一個不錯的黑暗之地， 也許是在沙漠，

you might see the center of our Milky Way galaxy

你也許能看到銀河系的中心，

spread out before you, hundreds of billions of stars.

上千億顆星星在你面前展開。

And it's a very beautiful image.

這是個非常美的畫面。

It's colorful.

非常多彩。

And again, this is just a local corner of our universe.

同樣的，這也只是 我們這個宇宙的一小角。

You can see there's a sort of strange dark dust across it.

你可以看到有種奇怪的、類似 暗色灰塵的東西橫越它。

Now, that is local dust

這是此處的塵埃，

that's obscuring the light of the stars.

它遮蔽了星體的亮光。

But we can do a pretty good job.

但我們可以看得很清楚。

Just with our own eyes, we can explore our little corner of the universe.

只要用我們的雙眼 就可探索宇宙中我們所處的小角落。

It's possible to do better.

還有可能看得更清楚。

You can use wonderful telescopes like the Hubble Space Telescope.

你可以使用很好的望遠鏡， 如哈伯空間望遠鏡。

Now, astronomers have put together this image.

天文學家做出了這張影像。

It's called the Hubble Deep Field,

稱為「哈伯深領域」，

and they've spent hundreds of hours observing just a tiny patch of the sky

他們花了幾百小時觀察 天空的小小一部分，

no larger than your thumbnail held at arm's length.

比你伸直手臂時看到的 指甲蓋的大小差不多。

And in this image

在這張影像中，

you can see thousands of galaxies,

你可以看到數千個銀河系，

and we know that there must be hundreds of millions, billions of galaxies

我們知道在整個宇宙中 必定有數億數兆個

in the entire universe,

銀河系存在，

some like our own and some very different.

有些很像我們的銀河系， 有些則非常不同。

So you think, OK, well, I can continue this journey.

所以你心想，好，我可以繼續這旅程。

This is easy. I can just use a very powerful telescope

這很簡單。 我只要用強大的望遠鏡對準天空，

and just look at the sky, no problem.

然後只要看著天空，沒問題的。

It's actually really missing out if we just do that.

但如果我們真的這樣做， 其實會錯過很多。

Now, that's because everything I've talked about so far

那是因為目前我所講的一切，

is just using the visible spectrum, just the thing that your eyes can see,

都只用到可見光譜，也就是 你眼睛可以看到的電磁波範圍，

and that's a tiny slice,

那只是極小的一部分，

a tiny, tiny slice of what the universe has to offer us.

宇宙一切中極小、極小的一部份。

Now, there's also two very important problems with using visible light.

使用可見光，會有兩個重要的問題。

Not only are we missing out on all the other processes

我們不只會錯過其他的景象──

that are emitting other kinds of light,

因為它們發出的是 其他種類的、不可見的光，

but there's two issues.

還有兩個問題。

Now, the first is that dust that I mentioned earlier.

第一我之前提到的灰塵，

The dust stops the visible light from getting to us.

灰塵阻擋，讓可見光無法傳到我們這裡。

So as we look deeper into the universe, we see less light.

所以當我們看向宇宙更深處， 我們看到的光就更少。

The dust stops it getting to us.

灰塵阻擋讓光無法傳到我們這裡。

But there's a really strange problem with using visible light

但當我們試圖使用 可見的光來探索宇宙時，

in order to try and explore the universe.

會有一個非常奇特的問題。

Now take a break for a minute.

現在先休息一下。

Say you're standing on a corner, a busy street corner.

假設你站在一個角落，繁忙的街角。

There's cars going by.

有車子經過。

An ambulance approaches.

有一輛救護車接近，

It has a high-pitched siren.

它有著高音頻的警笛聲。

(Imitates a siren passing by)

（模仿警笛經過）

The siren appeared to change in pitch

警笛朝你而來和遠離你時，

as it moved towards and away from you.

音高明顯有所不同。

The ambulance driver did not change the siren just to mess with you.

救護車司機並沒有改變警笛來玩弄你。

That was a product of your perception.

那是你的感知所造成的。

The sound waves, as the ambulance approached,

當救護車接近時，聲波

were compressed,

會被壓縮，

and they changed higher in pitch.

它們的音高會變更高。

As the ambulance receded, the sound waves were stretched,

隨著救護車離開，聲波被延展，

and they sounded lower in pitch.

警笛聲的音高聽起來就比較低。

The same thing happens with light.

光也有同樣的現象，

Objects moving towards us,

當物體向我們移動，

their light waves are compressed and they appear bluer.

它們的光波被壓縮，因此顯得比較藍。

Objects moving away from us,

遠離我們的物體，

their light waves are stretched, and they appear redder.

它們的光波被延展，因此顯得比較紅。

So we call these effects blueshift and redshift.

我們稱這些效應為藍移和紅移。

Now, our universe is expanding,

現在，我們的宇宙正在擴張，

so everything is moving away from everything else,

所以所有東西都在遠離其他東西，

and that means everything appears to be red.

那就意味著所有東西 看起來都是紅的。

And oddly enough, as you look more deeply into the universe,

奇怪的是，當你看向宇宙更深處，

more distant objects are moving away further and faster,

距離越遠的物體， 也在越快地遠離我們，

so they appear more red.

所以它們看起來變得更紅。

So if I come back to the Hubble Deep Field

如果我回到「哈伯深領域」

and we were to continue to peer deeply into the universe

並且我們持續窺探宇宙深處，

just using the Hubble,

僅僅只使用哈伯，

as we get to a certain distance away,

當我們到達一定距離之後，

everything becomes red,

每樣東西都變成紅色，

and that presents something of a problem.

那就呈現出了一個問題。

Eventually, we get so far away

最終，地方距離我們如此之遠，

everything is shifted into the infrared

一切都轉變成紅外線，

and we can't see anything at all.

我們就完全看不到任何東西。

So there must be a way around this.

那必須要有解決之道。

Otherwise, I'm limited in my journey.

否則，我的旅程將受到限制。

I wanted to explore the whole universe,

我想要探索整個宇宙，

not just whatever I can see, you know, before the redshift kicks in.

不僅僅是肉眼可見的部份， 可現在，「紅移」造成了麻煩。

There is a technique.

有一種技術，

It's called radio astronomy.

叫射電天文學。

Astronomers have been using this for decades.

天文學家已使用這技術數十年了。

It's a fantastic technique.

它是種很棒的技術。

I show you the Parkes Radio Telescope, affectionately known as "The Dish."

我讓你們看看帕克斯射電望遠鏡 也就是所謂的「碟子」（The Dish）。

You may have seen the movie.

你可能看過《不簡單的任務 （The Dish）》這部電影。

And radio is really brilliant.

無線電棒極了。

It allows us to peer much more deeply.

它可以讓我們能窺探得更深入。

It doesn't get stopped by dust,

它不會被灰塵阻擋，

so you can see everything in the universe,

所以你可以看到在宇宙中的任何東西，

and redshift is less of a problem

紅移問題就不算什麼了，

because we can build receivers that receive across a large band.

因為我們可以建造接收器 來接收很廣的波段。

So what does Parkes see when we turn it to the center of the Milky Way?

所以當我們把帕克斯轉向銀河的中央 我們會看到什麼？

We should see something fantastic, right?

我們應該會看到很炫的東西，對吧？

Well, we do see something interesting.

嗯，我們確實看到了有趣的東西。

All that dust has gone.

所有的灰塵都不見了。

As I mentioned, radio goes straight through dust, so not a problem.

如我先前提到的，無線電波可以 直接穿透灰塵，這不是個問題。

But the view is very different.

但看到的景象非常不同。

We can see that the center of the Milky Way is aglow,

我們可以看到銀河的中央在發光，

and this isn't starlight.

這不是星光。

This is a light called synchrotron radiation,

這種光叫做同步加速輻射 （synchrotron radiation），

and it's formed from electrons spiraling around cosmic magnetic fields.

它是由電子繞著宇宙磁場 螺旋轉動所形成，

So the plane is aglow with this light.

是這種光讓這個平面看來在發光。

And we can also see strange tufts coming off of it,

我們可以看到來自它的奇特簇束，

and objects which don't appear to line up

以及一些物體， 它們顯然並不符合

with anything that we can see with our own eyes.

我們肉眼所見的一切。

But it's hard to really interpret this image,

這個影像很難詮釋，

because as you can see, it's very low resolution.

因為如你所見，它的解析度很低。

Radio waves have a wavelength that's long,

無線電波的波長很長，

and that makes their resolution poorer.

這使得它的解析度更差。

This image is also black and white,

這個影像也是黑白的，

so we don't really know what is the color of everything in here.

所以其實我們不知道 那裡的任何東西是什麼顏色。

Well, fast-forward to today.

快轉到現今，

We can build telescopes

我們可以建造出

which can get over these problems.

能解決這些問題的望遠鏡。

Now, I'm showing you here an image of the Murchison Radio Observatory,

現在我要給你們看的是 默奇森電波天文臺的影像，

a fantastic place to build radio telescopes.

那兒是設置射電望遠鏡的絕佳地點。

It's flat, it's dry,

它很平坦，很乾燥，

and most importantly, it's radio quiet:

最重要的是，沒有電波幹擾：

no mobile phones, no Wi-Fi, nothing,

沒有手機，沒有無線網路，都沒有。

just very, very radio quiet,

就是完全無電波幹擾。

so a perfect place to build a radio telescope.

因此是設置電波望遠鏡的完美地點。

Now, the telescope that I've been working on for a few years

我這些年來工作中的望遠鏡

is called the Murchison Widefield Array,

叫「默奇森寬場陣列（MWA）」，

and I'm going to show you a little time lapse of it being built.

我要給各位看一段它建造過程的縮時影片。

This is a group of undergraduate and postgraduate students

這是一群大學和研究生，

located in Perth.

地點在伯斯。

We call them the Student Army,

我們稱他們為「學生軍隊」，

and they volunteered their time to build a radio telescope.

他們是自願協助架設望遠鏡的義工。

There's no course credit for this.

做這工作是沒有學分奬勵的。

And they're putting together these radio dipoles.

他們在裝配無線電的偶極。

They just receive at low frequencies, a bit like your FM radio or your TV.

它們可以收到很低的頻率， 有點像是FM廣播或電視。

And here we are deploying them across the desert.

我們將它們佈署到沙漠中。

The final telescope covers 10 square kilometers

最終望遠鏡含蓋了10平方公里。

of the Western Australian desert.

位在西澳洲的沙漠上。

And the interesting thing is, there's no moving parts.

有趣的是，沒有可活動的部件。

We just deploy these little antennas

我們只是佈署了這些小天線，

essentially on chicken mesh.

基本上是放在六角形網格上。

It's fairly cheap.

價格非常便宜。

Cables take the signals

從天線取得的信號

from the antennas

透過覽線

and bring them to central processing units.

被送到中央處理單位。

And it's the size of this telescope,

是因為這望遠鏡的大小，

the fact that we've built it over the entire desert

大到我們得在整個沙漠上建造它，

that gives us a better resolution than Parkes.

因而才有比帕克斯更好的解析度。

Now, eventually all those cables bring them to a unit

最後，所有這些覽線 把數據傳送給一個處理單位，

which sends it off to a supercomputer here in Perth,

處理單位又將資訊 傳到位在伯斯的超級電腦，

and that's where I come in.

這就是我發揮功能的地方了。

(Sighs)

（嘆氣）

Radio data.

無線電波資料。

I have spent the last five years

我花了過去五年

working with very difficult, very interesting data

處理非常困難但非常有趣的資料，

that no one had really looked at before.

都是過去沒人看過的。

I've spent a long time calibrating it,

我花了好多時間校調它，

running millions of CPU hours on supercomputers

花了數百萬中央處理器小時 來用超級電腦做運算，

and really trying to understand that data.

並真正嘗試去瞭解資料。

And with this telescope,

有了這個望遠鏡，

with this data,

有了這些資料，

we've performed a survey of the entire southern sky,

我們針對整個南方天空進行了一項調查，

the GaLactic and Extragalactic All-sky MWA Survey,

稱為「銀河系及銀銀河外星系的 全天空的 MWA 調查」。

or GLEAM, as I call it.

我簡稱它叫 GLEAM 。

And I'm very excited.

我非常興奮。

This survey is just about to be published, but it hasn't been shown yet,

這調查即將要發表， 但目前尚未公開過，

so you are literally the first people

所以你們就是最早

to see this southern survey of the entire sky.

看到這南方天空調查的人。

So I'm delighted to share with you some images from this survey.

我很高興能在此與你們分享 這次調查中的一些影像。

Now, imagine you went to the Murchison,

現在，想像一下你去默奇森，

you camped out underneath the stars

你在星空下野營，

and you looked towards the south.

你向南方看去，

You saw the south's celestial pole,

看到了南天極，

the galaxy rising.

銀河系在上升。

If I fade in the radio light,

如果我逐漸加強無線電的光，

this is what we observe with our survey.

我們的調查中所看到的 畫面就是這樣的。

You can see that the galactic plane is no longer dark with dust.

你可以看到 銀河平面不再因為灰塵而那麼暗了。

It's alight with synchrotron radiation,

同步加速輻射讓它亮起來，

and thousands of dots are in the sky.

天上有著數以千計的點。

Our large Magellanic Cloud, our nearest galactic neighbor,

我們的大麥哲倫雲， 也就是我們最近的銀河鄰居，

is orange instead of its more familiar blue-white.

它是橘色的， 而非我們比較熟悉的藍白色。

So there's a lot going on in this. Let's take a closer look.

所以這裡有很多學問， 我們再近一點看。

If we look back towards the galactic center,

如果我們回頭看銀河中心，

where we originally saw the Parkes image that I showed you earlier,

我先前給大家看的帕克斯影像，

low resolution, black and white,

是低解析度且黑白的，

and we fade to the GLEAM view,

我們漸漸轉換到 GLEAM 的畫面，

you can see the resolution has gone up by a factor of a hundred.

可以看到解析度提升百倍。

We now have a color view of the sky,

我們現在能看到彩色的天空了，

a technicolor view.

特藝彩色的天空。

Now, it's not a false color view.

畫面上的這些顏色並不是假的。

These are real radio colors.

它們是真實的無線電波顏色。

What I've done is I've colored the lowest frequencies red

我做的是將最低頻率設定為紅色，

and the highest frequencies blue,

最高頻率設定為藍色，

and the middle ones green.

中間頻率則是綠色。

And that gives us this rainbow view.

就產生了這個彩虹色影像。

And this isn't just false color.

這不只是假的顏色。

The colors in this image tell us about the physical processes

畫面中的顏色能告訴我們在宇宙中

going on in the universe.

所發生的物理過程。

So for instance, if you look along the plane of the galaxy,

比如，如果你延著銀河系的平面看去，

it's alight with synchrotron,

它因為同步加速輻射而亮著，

which is mostly reddish orange,

大部份是橘紅色，

but if we look very closely, we see little blue dots.

但如果我們非常近看， 可以看到些小藍點。

Now, if we zoom in,

如果我們把影像放大，

these blue dots are ionized plasma

這些藍點是電離的等離子體，

around very bright stars,

圍繞在非常亮的星體旁邊，

and what happens is that they block the red light,

原因是因為它們阻擋了紅光，

so they appear blue.

所以會顯現藍色。

And these can tell us about these star-forming regions

這些資訊能讓我們瞭解 我們的銀河系中這些由星體

in our galaxy.

形成的區域。

And we just see them immediately.

我們能立即看到它們。

We look at the galaxy, and the color tells us that they're there.

我們看向銀河系， 顏色就能顯示它們的所在。

You can see little soap bubbles,

你們可以看見小小的肥皂泡，

little circular images around the galactic plane,

在銀河系平面周圍的小圓圈，

and these are supernova remnants.

它們是超新星的遺跡。

When a star explodes,

當一顆星星爆炸，

its outer shell is cast off

它的外殼會被脫去，

and it travels outward into space gathering up material,

它會向外移動進入太空 收集物質，

and it produces a little shell.

產生出小的殼。

It's been a long-standing mystery to astronomers

對天文學家而言， 超新星的遺跡在何處

where all the supernova remnants are.

一直是長久以來的謎。

We know that there must be a lot of high-energy electrons in the plane

我們知道在平面中一定 有許多高能量的電子，

to produce the synchrotron radiation that we see,

才能產生我們看見的 同步加速輻射。

and we think they're produced by supernova remnants,

我們認為這些電子是 由超新星遺跡產生的，

but there don't seem to be enough.

但似乎光這些遺跡 還不夠證實猜測。

Fortunately, GLEAM is really, really good at detecting supernova remnants,

幸運的是，GLEAM非常擅長 偵測超新星遺跡，

so we're hoping to have a new paper out on that soon.

所以我們希望很快能 發表這方面的論文。

Now, that's fine.

好了，

We've explored our little local universe,

我們已經探索了我們所處的小宇宙，

but I wanted to go deeper, I wanted to go further.

但我還想要更深入，更進一步，

I wanted to go beyond the Milky Way.

我想要超越到銀河之外。

Well, as it happens, we can see a very interesting object in the top right,

這麼做時，在右上角可以 看到一個很有趣的物體，

and this is a local radio galaxy,

這是一個本地的射電星系

Centaurus A.

半人馬星座A。

If we zoom in on this,

如果我們把它放大，

we can see that there are two huge plumes going out into space.

可看到有兩大塊羽狀物 向外進入太空。

And if you look right in the center between those two plumes,

往兩塊羽狀物的中心看，

you'll see a galaxy just like our own.

你會看到一個星系 就像我們的銀河系一樣。

It's a spiral. It has a dust lane.

它是螺旋形的，有一道灰塵帶。

It's a normal galaxy.

是個正常的星系。

But these jets are only visible in the radio.

但只能透過無線電波 才能看得到這些噴流。

If we looked in the visible, we wouldn't even know they were there,

如果只看肉眼可見的部份， 就完全不會知道它們存在，

and they're thousands of times larger than the host galaxy.

它們比宿主星系還要大數千倍。

What's going on? What's producing these jets?

怎麼回事？這些噴流是如何形成的？

At the center of every galaxy that we know about

在我們所知的每個星系的中心

is a supermassive black hole.

都有個超大質量的黑洞。

Now, black holes are invisible. That's why they're called that.

黑洞是看不見的， 所以才叫黑洞。

All you can see is the deflection of the light around them,

只能看見它們周圍的光線偏折，

and occasionally, when a star or a cloud of gas comes into their orbit,

偶爾，當星體或氣體雲進入它們的軌道，

it is ripped apart by tidal forces,

會被引潮力給撕碎，

forming what we call an accretion disk.

形成我們所謂的吸積盤。

The accretion disk glows brightly in the x-rays,

用X光來看，吸積盤非常亮，

and huge magnetic fields can launch the material into space

強大的磁場能以近光速的速度

at nearly the speed of light.

將物質射入太空中。

So these jets are visible in the radio

所以從無線電波上可看到這些噴流，

and this is what we pick up in our survey.

這是我們的調查中發現的。

Well, very well, so we've seen one radio galaxy. That's nice.

好，我們看過了一個 射電星系，很好。

But if you just look at the top of that image,

但如果你看一下影像的上方，

you'll see another radio galaxy.

會看到另一個射電星系。

It's a little bit smaller, and that's just because it's further away.

它稍微小了一點， 那只是因為它比較遠。

OK. Two radio galaxies.

好，有兩個射電星系。

We can see this. This is fine.

我們能看見這些，沒問題。

Well, what about all the other dots?

那所有其他的光點又是什麼？

Presumably those are just stars.

假設它們都只是星體。

They're not.

但它們不是。

They're all radio galaxies.

它們都是射電星系。

Every single one of the dots in this image

這張影像上的每一個點都是

is a distant galaxy,

一個遙遠的星系，

millions to billions of light-years away

離我們有數百萬甚至數十億光年之遙

with a supermassive black hole at its center

中心有個超大質量的黑洞，

pushing material into space at nearly the speed of light.

將物質以近光速的速度推入太空中。

It is mind-blowing.

這太震撼了。

And this survey is even larger than what I've shown here.

這項調查比我們在這裡 所呈現的部份還要大。

If we zoom out to the full extent of the survey,

如果我們縮小影像來看整個調查，

you can see I found 300,000 of these radio galaxies.

可以看到，我找到了300,000個 像這樣的射電星系。

So it's truly an epic journey.

這真是段壯觀的旅程。

We've discovered all of these galaxies

我們發現了所有這些星系，

right back to the very first supermassive black holes.

追溯到最早先的超大質量黑洞。

I'm very proud of this, and it will be published next week.

我對此感到非常驕傲， 這項調查下週就會發佈。

Now, that's not all.

但還不只如此。

I've explored the furthest reaches of the galaxy with this survey,

這項調查中，我已經探索了 所能觸及的最遠的星系，

but there's something even more in this image.

但在這影像中呈現的還不只如此。

Now, I'll take you right back to the dawn of time.

讓我帶大家回到宇宙初開之時。

When the universe formed, it was a big bang,

當宇宙形成時，是一場大爆炸，

which left the universe as a sea of hydrogen,

讓宇宙變成了氫元素的海洋，

neutral hydrogen.

中性氫。

And when the very first stars and galaxies switched on,

當最早的星體及星系出現，

they ionized that hydrogen.

它們將氫給離子化了。

So the universe went from neutral to ionized.

所以宇宙從中性的變成離子化的。

That imprinted a signal all around us.

這在我們周圍留下了信號。

Everywhere, it pervades us,

無所不在，它滲透了我們，

like the Force.

就像原力一樣。

Now, because that happened so long ago,

因為這發生在非常古早之前，

the signal was redshifted,

這個信號發生了紅移，

so now that signal is at very low frequencies.

現在這個信號的頻率非常非常低。

It's at the same frequency as my survey,

和我的調查中的頻率一樣，

but it's so faint.

但它太微弱。

It's a billionth the size of any of the objects in my survey.

和我的調查中的任何物體相比 它只有十億分之一。

So our telescope may not be quite sensitive enough to pick up this signal.

所以我們的望遠鏡敏感度 不足以接收到這個信號。

However, there's a new radio telescope.

然而，有一個新的電波望遠鏡。

So I can't have a starship,

所以，我無法擁有一艘太空船，

but I can hopefully have

但我有希望能擁有

one of the biggest radio telescopes in the world.

世界上最大的射電望遠鏡之一。

We're building the Square Kilometre Array, a new radio telescope,

我們正在建造一個新的望遠鏡 叫「平方公里陣列」，

and it's going to be a thousand times bigger than the MWA,

它將會比默奇森寬場陣列 還要大上一千倍，

a thousand times more sensitive, and have an even better resolution.

敏感度高上一千倍， 解析度也更高。

So we should find tens of millions of galaxies.

我們應該可以發現上千萬個銀河系。

And perhaps, deep in that signal,

也許，在那信號中，

I will get to look upon the very first stars and galaxies switching on,

我可以找到最初的星體和星系。

the beginning of time itself.

找到時間的起源。

Thank you.

謝謝大家。

(Applause)

（鼓掌）