"The sun will leave a diamond the size of the Earth." Astronomer Mikhail Lisakov - about the evolution of stars

There are many myths that astronomers often encounter. For example, many are sure that Jupiter can someday turn into a star. And every star will explode at the end of its life.

Physicist and astronomer Mikhail Lisakov told on the forum "Scientists vs. Myths", which life path each star goes through. He also clarified what will happen to our Sun at the end of evolution, and explained why gold is a cosmic metal. This forum is hosted byANTROPOGENESIS.RU"- posted a video on their YouTube channel. And Lifehacker summarized the lecture.

What celestial body can be considered a star

There is a frivolous formulation: a star is an object from which we see rays.

Actually, this is not really a joke. If we look at photographs of space taken with telescopes, we will see foggy clouds and bright dots. Small specks of fog are galaxies. Luminous points with several rays are stars.

The optical system of a modern telescope is designed in such a way that when light is refracted in a photo, rays actually appear in the stars. But on ancient sky maps, when there were no such telescopes, people depicted stars in the same way.

To understand what the secret is, scientists conducted a small study. They shone into people's eyes with a small but bright source, and took pictures retina. It turned out that all the subjects on the retina produced very similar images. That is, a clear center and a cloud of thin lines intersecting at this point. So that's right: stars are bright celestial bodies that have rays.

And now seriously. To understand how a star differs from other space objectsLet's take a look at its center. There is a core in which a thermonuclear reaction is continuously going on. As a result, light elements turn into heavier ones and energy is released due to this transition. It is transferred to the outer layers of the star. For example, by mixing large masses of matter. This process looks like boiling water in a saucepan. This is how we see the surface of our Sun.

A continuous thermonuclear reaction is the main distinguishing feature of a star.

For such a fusion, it is necessary to bring positively charged particles, protons, very close together. To support this process, very high temperature and pressure are needed. And as a result of the reaction, one helium atom is obtained from two hydrogen atoms or four protons.

But it is known that four protons weigh more than this atom. So, you need to understand where the difference goes.

If three helium atoms are collided, then carbon atom is formed as a result of thermonuclear fusion. But this requires an even higher temperature. However, the process does not stop at carbon either. Then oxygen begins to be synthesized, then magnesium. And so on down to iron. The synthesis of heavier elements in the core of a star is no longer supported spontaneously. It needs additional energy from outside.

There is a myth that Jupiter also had to become a star, as Sun, but something happened to go wrong. This is a myth, because the mass of this planet is not enough to support a constant thermonuclear reaction. The temperature and pressure will not be high enough. Therefore, Jupiter can become a star only under one condition: it will increase its mass by about 15 times. But this is impossible.

What are the stars like?

If you look at the night sky on a clear day, you can see different types of stars:

• Bright or dim. It used to be thought that the less visible stars they are just further away from us. But then astronomers learned to measure distances to space objects. And they found out that the brightness of the luminaries does not depend on their distance, but on their power. For some stars, this parameter is indeed greater than for others.
• Multi-colored - blue, yellow, reddish, white. Different shades of stars are also not an illusion. Each of them has its own radiation temperature.

Scientists have built a graph where the horizontal axis is the temperature of the star, or its color. The vertical axis is brightness, saturation of light. Then we put all the known stars on this graph. And they saw that most of them were located diagonally - from the most powerful and hot blue giants to small red dwarfs. This diagonal was called the Main Sequence.

Massive and bright, hotter stars are located in the blue part of the spectrum. There are very few of them, and they live a relatively short time. But in the left, red region of the spectrum, we see much more stars. Their mass is much smaller, they are colder and shine weakly. But their lifetime is much longer than that of the blue giants. The sun is closer to the middle - in the yellow region of the spectrum.

But there are a few more areas on the chart. Consider those above the Main Sequence. Stars get there, in which, in the process of thermonuclear fusion, all hydrogen has ended, that is, burned out. It turns out a kind of "nursing home" for the stars - a place where the luminaries fall at the sunset of their lives. The fusion reaction is still going on in them and lighter elements continue to turn into heavy ones.

But there is another fairly noticeable area of ​​​​star clusters - below the Main Sequence. Astronomers call it the "graveyard."

How does stellar evolution happen?

Now let's talk in more detail about what events occur in a long stellar life.

Astronomers call all changes in the state of the stars stellar evolution. She has almost nothing in common with biological evolution. The only coincidence is that both processes continue for millions and billions of years.

Stellar evolution is a complete life cycle of each luminary. During this time, the star changes beyond recognition. But what kind of changes await her depends on the mass. It is possible to conditionally divide space objects into three groups.

1. Stars with low mass

For example, Proxima Centauri. They are born in a gas-dust cloud and become red dwarfs. And then they live for a very long time in an unchanged state, until they run out of hydrogen. Such a fate awaits a star if its mass is about 10 times less than the sun.

2. Stars comparable in size to the Sun

These are heavier and more interesting objects. Their mass is enough for the next stage, the synthesis of carbon from helium, to begin in the core after the combustion of hydrogen. As a result, they swell to the size of a red giant. For example, the Sun, as a result of this process, will increase so that it will swallow Mercury and Venus. And then it will grow almost to the orbit of the Earth. This will happen in about five billion years. It will be great if people find a way by then. be away from our light.

Then such a star sheds a shell, which turns into a planetary nebula. In the center remains a shining point - the former core. And the luminary conditionally moves to the cemetery.

3. massive stars

Their mass is more than 10 times greater than the sun. They live quickly, and in the end turn into either black holeor into a neutron star. We will talk in more detail about how the evolution of huge luminaries occurs.

How do neutron stars and black holes appear?

In very heavy stars, the temperature and pressure allow the thermonuclear reaction to continue up to the stage of iron formation. Therefore, in their structure, the nuclei of giants resemble onions. In the very center they have iron, then a layer of silicon, oxygen, neon, and so on.

When all matter turns to iron, the fusion engine is turned off. It is already energetically unprofitable for him to work further. Therefore, the radiation of the star stops. But gravity remains.

And then gravity forces all the outer layers to collapse and fly towards the center.

Then the star explodes like a supernova. But there are two options here:

1. Quantum forces will stop the collapse process. The density of the stellar matter left after the explosion will become so high that the electrons will be pressed into the protons and as a result form neutral particles - neutrons. Due to quantum effects, neutrons will not allow gravity to continue the process of compression. As a result, a neutron star is formed - an object with an extremely high density of matter.
2. Gravity is stronger than quantum forces. Then the process of collapse continues until the object turns into a black hole.

There is a myth that black holes will gradually absorb all the matter Universe. But it's not.

It happens that stars are born and live in pairs. Imagine that one turned into a black hole, and the other became a red giant. Then the first will slowly pull the substance from the second. A disk of hot particles forms around a black hole. If there are too many such particles, we will observe the reverse process.

Where did gold and other heavy metals come from in the universe?

We found out that iron and lighter elements are synthesized in the process of a thermonuclear reaction inside a star. Let's see how elements heavier than iron are formed.

This requires additional neutrons, and in large quantities. Under certain conditions, they can be “pushed” into the nucleus of an atom of a lighter element. As a result, neutrons can lose electrons in the process of beta decay. Then the neutral particles will turn into protons and the charge of the atom will increase. This means that there will be an increase in the serial number - the element will turn into a heavier one.

The question arises: where to get so many free neutrons. Previously, it was believed that a huge number of them appear after supernova explosions. But in 2017, scientists were able to observe another process - the merger of two neutron stars. The result is one object and a lot of debris. As a result, a “tsunami” arises from these fragments, which consists of pure neutrons. The density of such a flow is quite large - it is comparable to the density water.

A lot of neutrons are “pushed” into any atom that meets on the path of this stream. Then they decay into protons and electrons, and as a result, heavier elements are obtained. For example, gold.

Today, scientists know that most of the heavy metals in our universe were formed in this way.