The life cycle of a neutron star - David Lunney

譯者: Lilian Chiu 審譯者: Helen Chang

About once every century,

大約一個世紀會有一次，

a massive star somewhere in our galaxy

我們的銀河某處， 有一個大質量的星體

runs out of fuel.

把燃料用光了。

This happens after millions of years of heat and pressure

會有這種情況，是因為 數百萬年來，高熱和壓力

have fused the star’s hydrogen

將該星體的氫氣融入到 更重的元素當中，

into heavier elements like helium, carbon, and nitrogen— all the way to iron.

如氦、碳、氮，一直到鐵，

No longer able to produce sufficient energy to maintain its structure,

無法再產生出足夠的能量 來維持星體的結構，

it collapses under its own gravitational pressure and explodes in a supernova.

它的引力壓力會讓它自己垮掉， 發生爆炸，成為超級新星。

The star shoots most of its innards into space,

這個星體會把它的 內容物都射入太空，

seeding the galaxy with heavy elements.

在銀河中播下重元素的種子。

But what this cataclysmic eruption leaves behind might be even more remarkable:

但這種劇烈爆發 留下的東西或許更驚人：

a ball of matter so dense that atomic electrons

一個球形物質，密度非常高， 以致於原子的電子

collapse from their quantum orbits into the depths of atomic nuclei.

會從它們的量子軌道 落到原子核的深處。

The death of that star is the birth of a neutron star:

那個星體的死亡， 成了一個中子星的誕生：

one of the densest known objects in the universe,

中子星是全宇宙 最高密度的已知物體之一，

and a laboratory for the strange physics of supercondensed matter.

它也是超級壓縮物質的 奇異物理實驗室。

But what is a neutron star?

但，中子星是什麼？

Think of a compact ball inside of which protons and electrons fuse into neutrons

想像一個緊實的球體，

它裡面的質子和電子融入中子，

and form a frictionless liquid called a superfluid—

形成一種沒有摩擦力的液體， 叫做超流體，

surrounded by a crust.

被外殼包起來。

This material is incredibly dense –

這種材料非常緊密，

the equivalent of the mass of a fully-loaded container ship

等同於將滿載的貨櫃船的質量

squeezed into a human hair,

擠壓到一根人類頭髮中，

or the mass of Mount Everest in a space of a sugar cube.

或是將聖母峰的質量 擠壓到方糖的大小中。

Deeper in the crust, the neutron superfluid forms different phases

在殼的深處， 中子超流體形成不同的相，

that physicists call “nuclear pasta,”

物理學家稱之為「核麵條」，

as it’s squeezed from lasagna to spaghetti-like shapes.

因為它被從扁麵平擠壓成 義大利麵條的形狀。

The massive precursors to neutron stars often spin.

中子星的大質量前身通常會旋轉。

When they collapse,

當它們崩垮時，通常 有數百萬公里寬的星體

stars that are typically millions of kilometers wide

compress down to neutron stars that are only about 25 kilometers across.

會被壓縮到只有 二十五公里寬的中子星。

But the original star’s angular momentum is preserved.

但原始星體的角動量還被保存著。

So for the same reason that a figure skater’s spin accelerates

和花式滑冰選手把手臂收進來 就能加速旋轉是相同的道理，

when they bring in their arms,

the neutron star spins much more rapidly than its parent.

中子星的旋轉速度 會比它的母體更快。

The fastest neutron star on record rotates over 700 times every second,

紀錄中最快的中子星

每秒鐘能轉七百次，

which means that a point on its surface whirls through space

這就表示，它表面上的點 在太空中的轉動速度

at more than a fifth of the speed of light.

比光速的五分之一還要快。

Neutron stars also have the strongest magnetic field of any known object.

中子星的磁場也是目前 所知物體中最強的。

This magnetic concentration forms vortexes

這種磁力的集中，會形成旋渦，

that radiate beams from the magnetic poles.

從磁極放射出光束。

Since the poles aren’t always aligned with the rotational axis of the star,

因為磁極未必一定對齊星體的轉軸，

the beams spin like lighthouse beacons,

光束就會像燈塔指引信號一樣旋轉，

which appear to blink when viewed from Earth.

從地球來看就像是閃爍。

We call those pulsars.

我們稱之為脈衝星。

The detection of one of these tantalizing flashing signals

1967 年，天體物理學家約瑟琳貝爾

by astrophysicist Jocelyn Bell in 1967

偵測到這些誘人的閃爍訊號，

was in fact the way we indirectly discovered neutron stars

事實上，這就是我們一開始

間接發現中子星的方式。

in the first place.

An aging neutron star’s furious rotation slows over a period of billions of years

經過數十億年的時間，

年邁中子星的猛烈轉動會慢下來，

as it radiates away its energy in the form of electromagnetic and gravity waves.

因為它以電磁波 和重力波的形式耗掉能量。

But not all neutron stars disappear so quietly.

但並不是所有的中子星 都會如此安靜地消失。

For example, we’ve observed binary systems

比如，我們曾經觀察到雙星系統，

where a neutron star co-orbits another star.

就是一個中子星 和另一個星體共用軌道。

A neutron star can feed on a lighter companion,

中子星能以這個 比較輕的伙伴為食，

gorging on its more loosely bound atmosphere

吞食它比較沒有緊密結合的大氣，

before eventually collapsing cataclysmically into a black hole.

直到最後劇烈崩垮成為黑洞。

While many stars exist as binary systems,

許多星體以雙星系統的方式存在，

only a small percentage of those end up as neutron-star binaries,

但當中只有一小部分 最後會變成中子星雙星，

where two neutron stars circle each other in a waltz doomed to end as a merger.

也就是兩個雙子星 像跳華爾滋一樣繞著彼此，

最後注定會合併起來。

When they finally collide, they send gravity waves through space-time

當它們終於相撞時， 會透過時空發出重力波，

like ripples from a stone thrown into a calm lake.

就像把一顆石頭丟入 平靜的湖中會產生漣漪。

Einstein’s theory of General Relativity

愛因斯坦的廣義相對論

predicted this phenomenon over 100 years ago, but it wasn't directly verified

在至少一百年前 就預測了這個現象，

但它一直到 2017 年 才被直接驗證，

until 2017,

when gravitational-wave observatories LIGO and VIRGO

那年重力波天文台 LIGO 和 VIRGO

observed a neutron star collision.

觀察到中子星相撞。

Other telescopes picked up a burst of gamma rays and a flash of light,

其他望遠鏡發現 伽瑪射線爆發，還有閃光，

and, later, x-rays and radio signals, all from the same impact.

後來還有 X 光和無線電訊號， 通通來自同一次撞擊。

That became the most studied event in the history of astronomy.

那事件成為天文學史上 最被拿來研究的事件。

It yielded a treasure trove of data

它衍生出了珍貴的資料，

that’s helped pin down the speed of gravity,

協助確定了引力的速度，

bolster important theories in astrophysics,

支持重要的天體物理學理論，

and provide evidence for the origin of heavy elements like gold and platinum.

並為金和鉑這類重元素的 來源提供了證據。

Neutron stars haven’t given up all their secrets yet.

中子星還有未知的秘密。

LIGO and VIRGO are being upgraded to detect more collisions.

LIGO 和 VIRGO 已經被升級， 可以偵測到更多的撞擊。

That’ll help us learn what else

那能夠協助我們了解，這些高密度

the spectacular demise of these dense, pulsating, spinning magnets

閃爍旋轉的磁鐵在壯麗地死亡時，

can tell us about the universe.

還能告訴我們什麼其他 關於這個宇宙的知識。