How to detect a supernova - Samantha Kuula

210,217 views ・ 2015-06-09

TED-Ed


请双击下面的英文字幕来播放视频。

翻译人员: Haochen Wang 校对人员: Gabriella Hu
00:07
Just now, somewhere in the universe, a star exploded.
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刚刚,在宇宙的某一处,就有一颗恒星爆炸了。
00:12
There goes another one.
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接着,又有一颗爆炸了。
00:14
In fact, a supernova occurs every second or so in the observable universe,
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事实上,每秒种都有超新星。
00:20
and there is one on average every 25 to 50 years
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在巨大的宇宙里,每25至50年就会产生
00:23
in a galaxy the size and age of the Milky Way.
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似银河系大小和年龄的星系。
00:28
Yet we've never actually been able to watch one happen
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然而,我们从没机会目睹
00:31
from its first violent moments.
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爆炸的瞬间。
00:34
Of course, how would we?
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当然,这怎么可能呢?
00:37
There are hundreds of billions of stars close enough
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有上千亿颗恒星
00:39
that we could watch the supernova explosion
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在我们可观察到的范围内
00:42
break through the surface of the star.
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演变超新星爆炸。
00:44
But we'd have to have our best telescopes focused on the right one
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但真正去取得有力的数据 首先需要一台先进望远镜
00:48
at precisely the right time to get meaningful data.
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以及它精准的对焦与时间的拿捏。
00:52
Suffice it to say, the odds of that happening are astronomically low.
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不用多说,这个实践是很困难的。
00:57
But what if we could anticipate a supernova before its light reached us?
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或许,我们可以尝试在光线传达到地球前 预测超新星的发生?
01:01
That may seem impossible.
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这听起来不可能。
01:03
After all, nothing travels faster than the speed of light, right?
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毕竟,没有力量可以超越光速,不是吗?
01:07
As far as we know, yes.
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据我们所知,确实没有。
01:10
But in a race, fast doesn't matter if you take a detour
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不过,在竞赛中,速度不代表一切。
01:13
while someone else beelines it for the finish line.
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相比绕路,走直径才能胜出。
01:17
For exactly that reason,
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同样的道理
01:19
photons don't win the supernova race to Earth.
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最早往地球传达超新星的不是光子
01:22
Neutrinos do.
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而是中微子。
01:25
Here's why.
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这就是原因:
01:26
There are two types of supernova.
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超新星分为两类。
01:29
Type 1 is when a star accumulates so much matter from a neighboring star,
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第一类是当一颗恒星从周围累积足够的物质后
01:34
that a runaway nuclear reaction ignites and causes it to explode.
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失控核反应启动并致其爆炸。
01:40
In type 2, the star runs out of nuclear fuel,
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在第二类中,恒星耗尽核燃料
01:44
so the gravitational forces pulling in
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因此引力的作用
01:47
overwhelm the quantum mechanical forces pushing out,
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压倒量子力
01:51
and the stellar core collapses under its own weight in a hundredth of a second.
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使恒星的内核因自身重量的压力在百分之一秒内崩塌。
01:57
While the outer reaches of the star are unaffected by the collapsed core,
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虽然星系的外围不受内部的影响
02:01
the inner edges accelerate through the void,
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内缘在孔隙巨洞不断加速
02:04
smash into the core, and rebound to launch the explosion.
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直到核心受到重击,而以此爆炸。
02:10
In both of these scenarios,
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在这两类情况下
02:12
the star expels an unparalleled amount of energy,
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恒星将排出前所未有的能量
02:16
as well as a great deal of matter.
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以及大量物质。
02:18
In fact, all atoms heavier than nickel, including elements like gold and silver,
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实际上,所有比镍重的原子,包括金和银
02:24
only form in supernova reactions.
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只能在超新星爆炸中诞生。
02:28
In type 2 supernovae,
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在第二类超新星中,
02:30
about 1% of the energy consists of photons,
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大约1% 的能量是由光子组成的
02:33
which we know of as light,
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也就是我们所说的光。
02:35
while 99% radiates out as neutrinos,
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而其中的99%以中微子放射
02:39
the elementary particles that are known for rarely interacting with anything.
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它们的基本粒子很少交涉。
02:44
Starting from the center of the star,
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从恒星的中央
02:46
the exploding matter takes tens of minutes, or even hours,
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爆炸物需要数分钟,或数小时
02:50
or in rare cases, several days, to reach and break through the surface of the star.
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甚至有些时候花几天时间来抵达和突破恒星的表层。
02:58
However, the neutrinos, thanks to their non-interactivity,
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相比之下,中微子的非交互性质
03:02
take a much more direct route.
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促使它们选择更快的直径线路。
03:04
By the time there is any visible change in the star's suface,
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在恒星表面发生明显变化前
03:08
the neutrinos typically have a several hour head start over the photons.
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中微子就比光子占有时间上的优势。
03:13
That's why astronomers and physicists
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这就是为什么天文学家与物理学家
03:14
have been able to set up a project called SNEWS,
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建立了SNEWS项目,全称
03:18
the Supernova Early Warning System.
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超新星早期预警系统。
03:22
When detectors around the world pick up bursts of neutrinos,
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当探测器检测到微中子的存在时
03:25
they send messages to a central computer in New York.
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这些信息将被传输到位于纽约的中央计算机。
03:29
If multiple detectors receive similar signals within ten seconds,
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如果多个探测器在十秒内同时检测到信号
03:33
SNEWS will trigger an alert warning that a supernova is imminent.
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SNEWS会启动超新星爆炸警报。
03:37
Aided by some distance and direction information from the neutrino detectors,
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从微中子探测器提供的距离、方向等信息里
03:41
the amateur astronomers and scientists alike
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业余的天文学家以及科学家
03:44
will scan the skies and share information
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可通过扫描天空以及分享资料
03:47
to quickly identify the new galactic supernova
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从而识别新的超新星
03:50
and turn the world's major telescopes in that direction.
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并且将世界最高级的望远镜转到那个方向。
03:55
The last supernova that sent detectable neutrinos to Earth was in 1987
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在1987年最新探测到往地球 发送中微子的超新星处于在
04:01
on the edge of the Tarantula Nebula
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蜘蛛星云边缘
04:03
in the large Magellanic Cloud, a nearby galaxy.
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位于临近的大麦哲伦星系中。
04:07
Its neutrinos reached Earth about three hours ahead of the visible light.
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这些中微子比可见光提前三小时抵达地球。
04:12
We're due for another one any day now, and when that happens,
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现在,随时都有可能发生超新星爆炸
04:15
SNEWS should give you the opportunity to be among the first to witness something
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而当它发生的时候,SNEWS将给你一个千载难逢的机遇
04:21
that no human has ever seen before.
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来见证人类从未见过的场景。
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