Ep. 3: Early Chemical Evolution Ep. 3: Prima evoluzione chimica Ep. 3: Evolução química inicial Эп. 3: Ранняя химическая эволюция 第三集：早期化学进化 ep。 3：早期化學演化

Have you ever wondered how all the chemical elements are made? Then join me ||曾经|想过|||||元素||||| Вы когда-нибудь задумывались, как образуются все химические элементы? Тогда присоединяйся ко мне

as we are lifting all the star dust secrets to understand the cosmic origin of the |||提升|||||||理解||宇宙的|起源|| пока мы раскрываем все секреты звездной пыли, чтобы понять космическое происхождение

chemical element. Let's look at the early chemical evolution. Some 14 billion years 化学||||||||演化||十亿|

ago, everything started with a Big Bang. ||||||大爆炸 назад все началось с Большого Взрыва.

And it left behind the universe level made from just hydrogen and helium |||||宇宙|级别||||氢||氦 И он оставил позади уровень Вселенной, состоящий только из водорода и гелия.

gas. I mentioned before there's a tiny tiny little trace of lithium but we're not ||提到||有一个|||||微量||锂||| газ. Я упоминал ранее, что есть крошечный след лития, но мы не

going to worry about it. So we had a universe but they were no stars yet. |||||||||宇宙|||||| буду беспокоиться об этом. Итак, у нас была вселенная, но они еще не были звездами.

It was actually dark, and some people call that the cosmic Dark Ages. But ||实际上||||||||宇宙的||黑暗时代| На самом деле было темно, и некоторые люди называют это космическим Средневековьем. Но

structure began to form and gas began to clump, and so eventually, in a gas cloud 结构|||||气体|||团块||||||| структура начала формироваться, и газ начал слипаться, и, в конце концов, в газовое облако

the very first stars formed. Here are two of the first stars. And they were made |||星星|形成|||||||星星|||| образовались самые первые звезды. Вот две первые звезды. И они были сделаны

just from hydrogen and helium because the gas was just hydrogen and helium but for ||氢||氦气||||||氢||氦气|| только из водорода и гелия, потому что газ был просто водородом и гелием, но для

energy generation purposes, these stars needed to have nuclear fusion go on in 能量|能量生成|目的|||需要|||核|||| В целях производства энергии этим звездам нужно было, чтобы ядерный синтез шел в

their cores to produce energy. The first elements heavier than hydrogen |核心||产生|能量||||更重的||氢 их ядра для производства энергии. Первые элементы тяжелее водорода

helium were created inside of these stars, and later when they exploded as 氦气||创造的|内部||||||||爆炸| внутри этих звезд образовался гелий, а позже, когда они взорвались как

supernovae, they were expelled into this gas cloud. So we had the first elements 超新星|||被喷出||||||||||元素 сверхновых, они были выброшены в это газовое облако. Итак, у нас появились первые элементы

here, and of course they also gave the first light -- they lit up the universe for |||课程|||||||||||| здесь, и, конечно, они же дали первый свет -- они осветили вселенную для

the first time and changed it in a number of ways not just by bringing in в первый раз и изменил его несколькими способами, не только привнеся

light but also by producing the first heavier elements. That set in motion легкий, но и путем производства первых более тяжелых элементов. Это привело в движение

the chemical evolution of the elements. That's an ongoing process until today. Химическая эволюция элементов. Это непрерывный процесс до сегодняшнего дня.

Now these stars, here, because they formed from just hydrogen and helium gas were Теперь эти звезды, потому что они образовались только из газообразного водорода и гелия, были

very massive: rather large, maybe something like a hundred solar очень массивный: довольно большой, может быть, что-то вроде сотни солнечных

masses, so we use the unit of solar mass (this is a symbol for the Sun here) as a масс, поэтому мы используем единицу солнечной массы (здесь это символ Солнца) в качестве

unit. So 100 times as heavy as a Sun. The reason for that Ед. изм. То есть в 100 раз тяжелее Солнца. Причина этого

is that hydrogen and helium gas has trouble getting really cold что газообразный водород и гелий плохо охлаждаются

making small stars. The important thing with massive stars is that they have a изготовление маленьких звездочек. Что важно для массивных звезд, так это то, что они имеют

really short lifetime. They have a short lifetime of maybe a few действительно короткая жизнь. У них короткая жизнь, может быть, несколько

million years only. A few million years is not much for on a cosmic time scale только миллион лет. Несколько миллионов лет — это немного для космических масштабов времени.

which means they exploded pretty quickly as gigantic supernovae, and as already а это значит, что они взорвались довольно быстро, как гигантские сверхновые, и, как уже

indicated what happened at a later time these stars were gone but they left behind указывало на то, что произошло в более позднее время, когда эти звезды исчезли, но они оставили

all the heavy elements that they had created, and I should be specific here, все тяжелые элементы, которые они создали, и здесь я должен быть точным,

these heavier elements were all the elements made in fusion processes up to

(and including) iron. So we have fusion elements in the gas. With the onset of these (и включая) железо. Таким образом, мы имеем термоядерные элементы в газе. С появлением этих

little other elements being in the gas, now the gas could clump much

better and actually make small stars. So the next generation of stars, this was

the first generation, and, here, now we have the formation of

second-generation stars, here is a second-generation star, here's a

second-generation star -- so small stars similar to the Sun and perhaps a little

bit less massive than the Sun actually -- but of course you're not going to make

just small stars you're also going to make big stars. So we have a few big stars

here, again, a few intermediate ones and the big ones, the massive ones, will

again explode on a pretty fast timescale and make more elements. But these little

guys, and that's the interesting part for us here now,

so the low-mass second generation stars,

they have very long lifetimes, of something like 15 to

20 billion years because they had masses (at least some of them)

between 0.6 and 0.8 solar

masses, so less massive than our Sun. As a good rule of thumb, I can write this

here, the Sun has by definition one solar mass, and that has a lifetime, or

the Sun has a lifetime, of 10 billion years. So everything that has less mass

will have a longer lifetime and everything that is more massive than one

solar mass will have a much shorter lifetime. Now, what does this

imply? Having a long lifetime? It means that these stars are still around. They

are around today, we can observe them today, we can see them today, and that

means that we can use them to study the composition of this early gas here

because that's when they're formed. They have incorporated in all their layers,

throughout, the composition of this gas cloud that was enriched by

these very first stars. So we have means to study the first stars and what came out

of their supernova explosions, and what happened at this very early phase here of

star formation, galaxy formation, and the formation of all the chemical elements.

If you then wind the clock forward, many things happened after, well, of course

more stars formed, many many more stars, more supernovae,

and with every generation of supernovae, more of all the elements was provided

(more of all the elements) because as we will see later, in some of these very

early processes (nuclear physics processes) all the elements from the

periodic table were created already at the earliest times.

Then with time, more and more of all of them were created. It's not like that the

universe (because it was just hydrogen and helium in the beginning) then took

time to build up all the elements and marched through the periodic table with

time -- that is not the case. Everything was produced from early on, and then just

more and more off it. And so, well, we have more stars and more chemical

enrichment but also the formation of the first bigger structures

including the Milky Way.

Because this all happened in small gravitationally bound systems and they

were then gobbled up later by slightly bigger neighbors and then those were maybe

gobbled up by the proto-Milky Way, and eventually the Milky Way formed, and

formed from the remnants of all these little systems. All

of this here happened as time went on until today. Today we have a universe

that's full of structure and and full of all the elements, well, a whole 2%

but I think we can consider this "full" at least, you know, if you're an

astronomy. And chemical evolution is an ongoing process. So in

the following, we're going to look in more detail at chemical enrichment and

chemical evolution and also stellar archaeology which is the way how you

all stars to trace these different early stages of chemical evolution.