domeet webmaster

This article is from WeChat official account:Gezhilun Dao Forum (ID: SELFtalks), author: Shen Jun too (Shanghai Astronomical Observatory, Chinese Academy of galactic dynamics delegations Principal Investigator), head Figure from: vision China

“We all know this poem by Su Dongpo, “I don’t know the true face of Mount Lu, but we are only in this mountain.” Because we live in the galaxy, it is difficult for us to see the entire galaxy.”

Today I want to tell you something about the Milky Way.

This is a photo of a starry sky.

I would like to ask everyone here, who has actually seen the Milky Way?

It seems that there are very few, which is also normal, because the sky in Shanghai is a bit too bright and there is haze, so we can’t see the starry sky clearly.

If we look at the nearby mountains, the starry sky is very beautiful.

The Milky Way is the dark band of light and dark in the picture, and the Milky Way is the galaxy where the sun is.

The sun and other stars are not evenly distributed throughout the universe, but as a collective, and then distributed throughout the universe.

Just like human beings are not evenly distributed on the surface of the earth, we live in cities, and there are very few people in the areas between cities.

We just said that the Milky Way is the dark zone in the picture. Are these stars not in this dark zone belong to the Milky Way?

Actually, these stars are very close to us and belong to the Milky Way.

If we think of the Milky Way as a plate, all the stars that we can see with the naked eye are in this small red circle in the picture.

So we feel that the stars in the Milky Way seem to be distributed in all directions, but in fact they are all in the Milky Way.

This is another very beautiful starry sky. It was taken on a 5,000-meter high mountain in Chile. It is one of the best observation sites in the world.

We can see that there are some other celestial bodies besides the stars in the photo.

After humans learned to use telescopes, we have a deeper understanding of these celestial bodies.

For example, the Andromeda Nebula and the M33 Nebula. There are other celestial bodies, such as globular star clusters, which are very beautiful. It is formed by 10,000 stars gathered in a very small space.

So are these celestial bodies (nebulae and star clusters) in the Milky Way?

I will leave the answer to this question behind.

What is the Milky Way?

We live in the Milky Way, and naturally, we want to know what the entire Milky Way looks like.

We all know that Su Dongpo’s poem “I don’t know the true face of Mount Lu, only because I am in this mountain.” Because we live in the galaxy, it is difficult for us to see the full picture of the galaxy.

Someone may think that if we build a spacecraft and fly out of the entire galaxy, can we not see the whole picture?

The farthest aircraft created by mankind is called Voyager 1, and it currently runs at a speed of 60,000 kilometers per hour.

We know that China’s high-speed rail has a maximum speed of 300~350 km/h. This spacecraft is 200 times faster than our high-speed rail. If we take this spacecraft, it will only take one minute from Beijing to Shanghai!

Then if we fly out of the galaxy on Voyager 1, guess how long it will take?

50 million years!

We human beings have only five thousand years of written history. Obviously, this is a fantasy. It is impossible for us to fly out of the galaxy to see the entire galaxy.

But we can still ask these questions, what does the galaxy really look like? Is the Milky Way unique? Why did the Milky Way evolve into what it is now?

Astronomers have been asking the answers to these questionscase.

About 250 years ago, British astronomer Herschel first outlined the size of the Milky Way.

In this picture, we can see that he believes that the sun is near the center of the Milky Way. The Milky Way is a flat structure with a diameter of 6,400 light-years and a thickness of 1,300 light-years.

More than a hundred years later, the famous American scientist Sharpley studied the spatial distribution of globular star clusters and discovered that the sun is actually not in the center of the Milky Way, overthrowing the 500-year-old heliocentric theory, which is what we humans believe Know a huge leap in the history of the universe.

There are many small circles in this picture. Each small circle represents a globular cluster. Each globular cluster contains 10,000 to 100,000 stars. It is very bright, so we can see it from far away it.

The small yellow star in the picture represents the sun. At that time, Sharpley made a very bold assumption. He assumed that the globular cluster is a child of the Milky Way.System, then the center of the globular cluster should be the center of the Milky Way.

But through measurements, he found that the sun is not in the center of these globular clusters, so he boldly speculated that the sun is not in the center of the Milky Way.

And he believes that the Milky Way is the entire universe, and the beautiful spiral galaxies we saw just now are all within the Milky Way.

Of course, not every scientist agrees with Sharpley’s view.

In 1920, the American Academy of Sciences broke out a great debate on the scale of the universe. One group was represented by Sharpley and the other was represented by Curtis.

Sharpley’s school believes that the Milky Way is very large, it is the entire universe, and the spiral galaxy is the gas cloud in the Milky Way.

Another point of view is that spiral galaxies are outside the Milky Way, they are star systems, not gas clouds, and each nebula is like the Milky Way, an island universe, and the entire universe is composed of many galaxies. The island universe constitutes.

If the universe is an ocean, then every nebula is like the Milky Way, an island floating on the ocean.

Measure the distance of the nebula

There was no winner in this controversy at that time, mainly because there was no good observation equipment at the time and our scientific knowledge was also very lacking.

So please think about it, how can we best answer this question?

If we have a astrometer, we can accurately measure the distance to the nearest nebula. If this distance is greater than the known scale of the Milky Way, they are outside the Milky Way, otherwise they should be inside the Milky Way.

At that time, everyone had begun to realize that there was a very interesting variable star that could be used as a good ruler.

This kind of variable star is called a Cepheid variable star. A variable star is the periodic change in brightness of the star in the sky.

By measuring the light cycle of a Cepheid variable star, we can deduce its own luminosity. After knowing its own luminosity, we can measure the distance by comparing it with the apparent brightness.

It’s like we know how bright a candle is. If we see it very bright, it means it is very close to us, if we see it very dark, it means it is very far away from us.

Four years later, Hubble found this type of Cepheid variable star in the Andromeda Nebula.

Hubble is a very famous astronomer, and a space telescope flying outside the earth is named after him, the Hubble Space Telescope.

The picture on the left shows Hubble using a telescope for observation. He used the Hooke 2.5-meter telescope, the world’s largest telescope, which was just completed at that time.

With this weapon for observing the sky, Hubble studied the Andromeda Nebula in great detail, and he discovered that there are many Cepheid variable stars in it.

He assumed that these Cepheid variable stars belong to the Andromeda Nebula, and they can beThe distance to launch the Andromeda Nebula is the distance from us.

He concluded that this distance is about 1 million light-years, far greater than the known 300,000 light-years of the Milky Way at the time.

So he proved that the Andromeda Nebula is outside the Milky Way, and the Milky Way is not the entire universe.

After Hubble, we gradually realized that galaxies are the basic components of the universe, and there are countless island universe galaxies like the Milky Way in the universe.

The galaxy can also be subdivided into several categories. The picture on the left is an elliptical galaxy, and the right is a spiral galaxy. The spiral galaxy is like a plate. This is how it looks from the front. It has a beautiful spiral arm structure. .

Spiral galaxies can be subdivided into two types, one is called normal spiral galaxies, and the other is called bar-shaped spiral galaxies.

Then what kind of galaxy does our Milky Way belong to?

In order to answer this question, let’s re-examine the Milky Way we see in the visible light band.

We can see that there are many dark bands in the Milky Way. Why are these dark bands dark?

Because there is a lot of dust in the Milky Way, the dust will block our vision, just like haze, these things behind the dust are blocked by the dust and appear in the skyIt is a dark area.

In order to solve this problem, we can go to the infrared band to take a look. This is the Milky Way seen in the infrared band.

Infrared light has a longer wavelength than visible light, so this light can penetrate dust and let us see the stars behind it, so these dark bands disappear.

What we see is a flat disk structure, so the Milky Way is a spiral galaxy.

In addition, we will notice that there is a very bright object in the center of the Milky Way galaxy. This object is called the nuclear ball. About 1/3 of the stars are located in the nuclear ball, so it is very important.

This is the Milky Way we see from the side, so what does the front view of the Milky Way look like?

As we mentioned earlier, we are within the Milky Way, and it is difficult to see its full picture, so what should we do?

There is a way. I will give you an analogy. If there is no mirror in the world, you don’t know what you look like, but you can take a look at your brothers, sisters, relatives and friends, and calculate what you look like. Look like.

If they have one nose and two eyes, then you may also have one nose and two eyes.

So we can go outside the galaxy to find inspiration.

This is a brother and sister of the Milky Way, called UGC 6093.

It is a spiral galaxy with beautiful spiral arms and a long bar in the center. In addition, it also has a very bright center called the central nuclear ball.

Is the nucleus of this galaxy the same thing as the nucleus of our Milky Way?

Regarding the nucleus, there is a classic theory in the astronomy circle. They believe that the nucleus of spiral galaxies is produced during the merger of galaxies.

If there are two galaxies, one large and one small, the large one will eat the small and form a larger spiral galaxy with a nuclear ball in the center.

Does the classical theory also apply to our galaxy?

Now I want to remind everyone to pay attention to these two points. First, the left side of the nucleus at the center of the Milky Way looks larger than the right; second, this nucleus does not look like the ellipsoidal structure we see from the side.

So when I was a postdoctoral fellow in the United States, I became interested in this issue. After returning to China, I started research on this subject.

We put forward a hypothesis. Perhaps the nucleus of the Milky Way is not produced by the merger of galaxies, but by the spontaneous generation of the silver disk.

In order to confirm this hypothesis, we first need to derive some formulas, and then put our theory into the computer, and let the computer simulate the motion of each star.

Finally, we can build a model of the Milky Way, and then compare this model with our existing observations to see if the two are consistent.

This is a model of ours. In the beginning, the Milky Way was not a rod. It was a disk. Gradually, it would acquire a rotating rod.

After the rod is formed, look at the side, the Milky Way seems to have a wave-shaped instability. After this instability is saturated, the center becomes very thick.

So we think that the nuclear ball is the rod of the Milky Way seen from the side.

Our model agrees very well with the observations at the time. The picture on the left is a comparison of the morphology of the nucleus, You will see that the nuclear ball on the left is bigger and the nuclear ball on the right is smaller.

Because the direction of the rod is at an angle to the direction of our line of sight, we see the proximal end of the rod on the left and the far end on the right, so the near end appears larger than the far end.

More importantly, our model agrees very well with the kinematics data of the Milky Way, and our model can explain these observed data points very well.

Our work has also promoted the scientific community’s in-depth understanding of the Milky Way. This is a frontal top view of the Milky Way drawn by the artist based on scientific data. In this picture, the lower point is the solar system.

Bar in the Milky Way

If you compare the Milky Way to Shanghai, the center of the Milky Way is Shanghai’s People’s Square, but the sun is not in the center of the Milky Way, and the sun is on the outskirts, which is probably the location of Hongqiao Airport. In the center of the Milky Way, there is a long bar. The English name is Bar.

Bar has another meaning, bar, where is the easiest place to find a bar in the city?

The center of the city.

Our view is that the nucleus of the Milky Way we see is actually the rod of the Milky Way seen from the side.

The picture above is a typical Galaxy bar, with many aliens drinking.

What goes well with wine?

Peanuts.

We actually found a peanut in the center of the Milky Way.

We believe that the original shape of the Milky Way is a peanut-like structure.

The picture on the left is not actually turning the nuclear ball, but our perspective is turning, giving people a three-dimensional feeling.

The nucleus in the Milky Way can also be seen in other galaxies. At the bottom left of the picture on the far right, there is a galaxy containing a peanut-shaped nucleus, which looks very much like a peanut.

In this bar, we also found other very interesting things to eat.

In the peanut sphere, the star has a very unique orbit. The picture on the left is the orbit of the star. The top view is the top view, and the bottom is the side view. From the side, the star’s orbit is very similar banana.

We also found some star orbits like pretzels.

After our research was officially published, it received a lot of attention from the scientific community.

Unexpectedly, our work has also attracted the attention of theological circles.

This is a screenshot of the headline of a Christian website in the United States. The title is “The Milky Way is not an ordinary galaxy”, so the Milky Way must be created by God.

This person is a PhD in Astrophysics from the University of Toronto, but later he devoted himself to finding signs of creationism from scientific discoveries. This is a quotation from our paper.

But in fact, they only saw the abstract of our paper and wrote that headline with excitement. In fact, we clearly wrote in the main body of the paper that our Milky Way is not actually a unique galaxy.

The Milky Way looks like NGC 4565 from the side.

In the scientific world, generally speaking, if our work is cited or evaluated by other people, we will feel very happy and proud, but it is a very embarrassing feeling that our work has been cited by the theological world.

I believe that everyone has a general understanding of scientific research methods through what I have said.

Scientific research always starts with observations or experimental facts, and then proposes hypotheses and models.

First of all, your theory must be able to explain the existing observations, but most importantly, your theory must also give some predictions that we have not observed. Observers will then follow this direction to observe and go. Experiment.

If your prediction is confirmed, congratulations, your theory has passed a new round of tests.

But if these predictions are not confirmed, it means that your model needs to be modified, or even wrong, and a new model needs to be proposed.

It’s like Sharpley overthrew the heliocentric theory, but he was also proved by Hubble that many of his views were wrong.

The work we have done on the Milky Way model may be proven wrong by others in a few years. Our scientific research is always in such a spiraling process.

In the process of studying the galaxy and the universe, I am always moved by the sentence, “The most incomprehensible thing about the universe is that it is actually understandable.”

Our small human beings have only a few thousand years of written history, and the germination of science is only a few hundred years old. We can actually learn so many mysteries about the universe, which in itself is a very surprising thing. thing.

Finally, I would like to use this limerick to thank the SELF forum.

Knowing heaven and breadth by studying things,Geng Geng Yinhe has a road to climb.

This article is from WeChat official account:Gezhilun Dao Forum (ID: SELFtalks), author: Shen Jun too (Shanghai Astronomical Observatory, Chinese Academy of galactic dynamics missions principal investigator)