“The iron in our blood, the calcium in our bones, the oxygen we breathe every time, all these are from the stars long before the earth was born Refined in the furnace.” This article is from WeChat public account: On the Road Gezhi rostrum (ID: SELFtalks) , author: Li Haining, the picture of the title comes from: Visual China
Li Haining: Associate Researcher, National Astronomical Observatory, Chinese Academy of Sciences
Today I tell you the secrets of the distant stars, and the origin of life matter, which the stars in the sky tell us.
Like every mother, when I’m in a bad mood, I just look at my son and I feel that nothing is a problem.
But as a mother who studies astronomy, I can still see a very strange thing in him, that is the universe 13 billion years ago, do you believe it?
His body is made up of many elements like us.
There are six main types, including hydrogen and oxygen in water, carbon in organic matter, calcium in teeth and bones, nitrogen in protein, and phosphorus, which powers our cells.
Don’t think my son is only 2 years old, but thisThese elements have actually traversed tens of billions of years in the time and space of the universe. Do you think I am telling a science fiction novel?
The star produces all the elements
The story begins in the 1940s. At that time, people only knew that the Big Bang produced hydrogen, helium, and lithium. They didn’t know where the other elements came from.
At this time, a British astronomer named Fred Hoyle stood up and said: “It is the stars that produce all the elements.”
He published an article, but it didn’t attract much attention in the academic world.
So he found three very powerful helpers, and these four scientists worked hard for several years.
Finally, in 1957, an important article was published. They gave a complete theory of how stars synthesize elements.
The inside of a star is a high-temperature, high-pressure cosmic melting pot. All the elements we can see on the periodic table are produced here.
Don’t read that this article has no eye-catching title, nor was it published in Nature, but it won the Nobel Prize in Physics.
Although it is a pity that it is not Hoyle who won the prize, his non-mainstream views have indeed refreshed our understanding of the origin of the universe.
So now we know that the cosmic melting pot in the star has been producing various chemical elements since 13 billion years ago.
How did so many elements travel through tens of billions of years and finally come to the solar system and enter our bodies?
Let’s watch a video. About 13.7 billion years ago, with a “bang”, the universe had a big bang.
The explosion of the universe produced a lot of hydrogen, some helium, and extremely small amounts of lithium in about 3 minutes.
This big bang “paste” began to cool down. When it was cooled for about 200 million years, the first generation of stars appeared in the universe, and they began to make new chemical elements.
These stars are very bright and huge, and they ended their short life in an extremely powerful way-supernova.
And the chemical elements they produce are sprayed in all directions and passed on to the next generation of stars.
That’s it, generation after generation of stars can be described as successors, making the types and quantities of chemical elements in our universe continue to increase.
Until one day, when life in the solar system happens to be formed, we will appear.
Because of this, the very classic monologue in “Magical Furnace”: “In order for us to live, billions, tens of billions, or even hundreds of billions of stars have died. strong>
The iron in our blood, the calcium in our bones, the oxygen we breathe every time, all these are refined from the furnace of the stars long before the birth of the earth. “
This is a very familiar periodic table of elements. Does anyone think it’s big heads when they see it?
Astronomers are very humane. They invented a special periodic table. We call all elements heavier than helium metals.
Attention is all the elements heavier than helium, not just the metals in our daily concepts, the sum of these metal elements is called the metal content.
As the universe continues to age, the “snowball” of metal content is getting bigger and bigger. Each generation of newly born stars will have higher metal content in their bodies than their ancestors. One generation is a little bit more.
Until today, These “little flesh” stars, they have inherited the legacy of thousands of generations of stars, so the metal content in their bodies is already 13 billion years ago. 2 million times.
If one day you happen to come across a star with very low metal content, congratulations, you have seen the very early days of the universe.
I want to ask you a question, Do you think we can see the earliest stars?
Due to our current observing ability, the first generation of stars is just like the Yellow Emperor Yao and Shun, just a legend to us.
The oldest stars that we can directly observe are actually their direct descendants. These stars have not had time to accumulate much metal, so we call them metal-poor stars.
Don’t look at the name, but they are not “poor” at all in the meaning of the evolution of the universe.
If the current universe is 100 years old, when these metal-poor stars were born, the universe hadn’t gone to school, so there are many important information about the “infancy” of the universe hidden in their bodies.
This is why astronomers affectionately call them “cosmic fossils.”
There are still many questions about the origin of our human life elements, such as iron in our water and calcium in bones.
When was it first produced in the universe?
The origin of human life elements
Are there similarities between the chemical composition of the early universe and us today? Extracting the chemical composition of these metal-poor stars is the only way we can get the answer.
If you were to extract the chemical composition of a star now, what would you do?
Obviously we can’t move the stars back to the laboratory or office to study, so astronomers use telescopes to observe them.
When it comes to stargazing, astronomers should be excited. Everyone will have a variety of beautiful starry sky in their minds.
But the stars in my eyes are not the same as everyone imagined. This is the star I see. This is actually a two-dimensional spectrum of stars.
The horizontal layers you see are stars of different colors that we can see in our eyes.
These vertical lines are the absorption of hot starlight at specific wavelengths when passing through the cooler outer atmosphere.
In other words, each of these dark lines is a specific message left to us by a certain element in the starlight.
Show you a picture. Is the two-dimensional spectrum somewhat similar to this picture?
This picture is the human genetic map. So it is not an exaggeration to say that the stellar spectrum hides the genes of the stars, but how do we extract these genes?
This will use the more common one-dimensional spectrum in astronomical research.
How do you feel when you see this spectrum?
Very monotonous, even a bit dense and scary.
But I am responsible to tell you that this is the best one-dimensional spectrum I have found.
Don’t underestimate it, it is very useful.
By measuring the intensity of the spectral line inside, we can not only know which elements the star makes, and how much.
By combining the conditions of its outer atmosphere, we can even know the star’s age, weight, and place of birth.
And whether there have been violent conflicts with nearby stars recently. Therefore, the stellar spectrum is a great artifact for us to detect stars and extract planetary DNA.
I still remember the first time I discussed a research topic with my supervisor, he gave me two spectra for me to choose. Are you going to be a young star similar to the sun? Still going to study metal-poor old stars?
I chose Metal Poor Star, and at the time I was very satisfied with my decision.
I am curious how many secrets of the early universe are hidden by these ancient stars.
There is also a very important reason, because I know that the most time-consuming, labor-intensive, and easiest to crash in stellar spectrum analysis is to measure the spectrum.
There are so few lines in the spectrum of metal-poor stars, I can save a lot of time to measure the lines.
But soon I found out that my wishful thinking was wrong, because young stars like the sun are easy to find, but old stars with poor gold metals are very hard to find. How hard is it to find? I will show it to you.
For example, if you swipe around the sun, you can find so many stars.
But all the blue ones are young stars, and only the red ones are the metal-poor stars I am looking for.
Where is red?
There are only these. The first time I knew it, it was also the first time I personally realized what is called “the whole person is bad”!
But I was lucky enough to meet a very capable assistant, the Guo Shoujing telescope designed and built by our country.
It is an out-and-out stargazer. It can capture the spectra of more than 3000 stars with a blink of an eye.
So, it took 5 years to obtain more than 9 million celestial spectra, and of course I took the opportunity to make a big profit.
It was precisely based on this time that the metal-poor star made a fortune, and I got my first metal-poor star surprise.
I found an extremely old super metal-poor star. This star is almost 13 billion years old, and the old one is almost the same as the universe.
In the stellar world at that time, its age has ranked among the top 20 in the world.
But it’s very strange that I actually detected hydrogen, carbon, calcium, and iron in the spectrum of this star. These elements are all very important elements in our human life.
So, I realized once again that these elements in our bodies are far greater than the evolutionary history of our entire human race.History is too old.
Because the metal-poor stars I studied, they are very far away.
Melancholic metal-poor star
If we carefully observe its spectrum, we need to use the largest telescope in the world.
Guess what is the best place for astronomical observation in the northern hemisphere?
Yes, it’s in Hawaii.
When it comes to Hawaii, what do you think of?
The sun, the beach, the waves, the swaying hula dance, I set out with this kind of vision when I first went to observe.
But when I got off the car from base camp, I was stunned!
Did I go to a fake Hawaii?
So I thought I might be a quiet astronomer.
Usually we need to adapt to the base camp at an altitude of 2,800 meters just now for one or two nights, and then we can go to the top of Mauna Kea at 4,200 meters for observation.
There are many high-end, atmospheric and high-end telescopes in the world gathered on this mountain, one of which is my mostThe Pleiades Cluster Telescope often used.
The diameter of this telescope is 8 meters, so you may not know how big it is. Please pay attention to the lower left corner. These two things that are not clear are two SUVs.
So you can imagine what kind of behemoth this telescope is.
When we make observations, we usually stay in this place called the “observation room” from 5 pm that day until 7 am the next morning.
We control the telescope here, choose which star to observe, and check the observation data we get.
Don’t look at this room, it doesn’t seem to be very luxurious. Its price is so high that it surprises you-$80,000 per night.
The first time I went, I also found it very novel. I have to get better at such an expensive place.
But I found out that when I wandered the room, an observation assistant kept staring at me. I was puzzled.
After I asked, I found out that there was an American guy the night before, and he was the first time to observe.
He was very excited. In the observation room at an altitude of 4200 meters, he stood up suddenly and vigorously once, which caused him to complete the observations in the middle of the night while lying down.
Here, I met my second metal-poor star surprise.
In one observation, the weather on the next day was not particularly good, and there were no stars in sight, so I had to stop working and start chatting.
At 3 o’clock in the morning, I felt a little bit awkward to chat.
It’s a waste of $80,000 in one night. It’s a shame. Let’s play with the spectral data of the previous day.
During the analysis process, I found that there was a problem with a spectrum.
Everyone pay attention to the 6700 angstroms in the lower left corner. There shouldn’t be any spectral lines.
We conducted repeated investigations and finally proved that this is not a data error, but a real and very strong Li absorption line.
Someone may be asking, isn’t it just a Li is detected? Is it necessary to be so excited?
For our human body, Li element is a trace element, but it is also a very important life power element. It is the only metal element produced in the Big Bang.
Although it is said that Li can be synthesized inside our stars, the life of Li synthesized by stars is very short and can hardly survive for long.
So now, The Li in our mobile phones and the Li in the battery of new energy vehicles, and even the Li in the largest Li mine on earth, all come from the first 3 minutes of the Big Bang.
For stars, Li is also a trace element, so usually we can only see weak Li absorption lines in the spectrum, or not at all.
The classic theory and previous observational data also tell us that the Li content of metal-poor stars is extremely low.
That’s why I was so surprised to see such a strong Li absorption line in the spectrum of a metal-poor star.
In the following year and a half, we found several such strange metal-poor stars one after another.
The Li content of these guys is dozens of times higher than normal, even hundreds of times.
When I discovered this fact, my first reaction was that I could challenge the classical theory.
But a theoretical collaborator told me that you don’t get too proud of it too soon, there are other possibilities to explain where these Lis come from.
For example, there is a neighbor living next to this metal-poor star, it likes to collect Li, when the metal-poor star is close to it.
Went by the way; or there was a small celestial body with a lot of Li, which happened to pass by this metal-poor star and was eaten into the stomach by it.
With a very nervous mood, I turned up all the data I could use, but the result was very good, and there is no evidence to support the process they said.
I am very happy now, because I can finally cause a little trouble for the observer.
Soon, our discovery was reported by Science News, and I was happy for several days.
I always joked that These metal-poor stars are melancholic little stars, because the Li element they lack can not only make batteries, but also suppress depression It is the main ingredient of medicine to relieve symptoms and relieve mood.
Now that these metal-poor stars have suddenly received such a large batch of Li, will their mood be much better?
I don’t know, but I can be sure that the theoristTime to be depressed for a while.
I have been with metal-poor stars for ten years. At the beginning, I set myself a small goal: I can deal with one or two hundred stars.
But in ten years, I processed the data of nearly ten million stars and measured the intensity of hundreds of millions of spectral lines.
I know today that even among the oldest stars, we can detect elements such as hydrogen, helium, carbon, nitrogen, oxygen, calcium, iron, lithium, etc., which are very important for human life.
And phosphorus, which we thought could only be synthesized on the earth, has also been discovered in ancient stars nearly ten billion years old in recent years.
So I’m still curious, When did our universe reach its first chemical maturity and form life?
Why do people always say that a planetary system with life can only be found near young stars like the sun?
Will the earliest life that we don’t know was formed at the very early stage of the universe?
Of course, all these mysteries need more metal-poor stars to help us solve them.
And support me to continue on this path to the universe 13 billion years ago.
Another point is that I have always believed that these seemingly inconspicuous old stars will bring me unexpected new surprises sometime in the future.
This article is from WeChat official account:Gezhi Lundao Forum (ID: SELFtalks) author: SOCIALIST