Shulou(Shulou.com)11/24 Report--

Why is the sun a third-generation star? where is the remnant of the previous generation of stars (whether it's a neutron star or a black hole)?

The story begins 13.7 billion years ago. At that time, there was almost only hydrogen and a small amount of helium in the universe, and slowly they formed molecular clouds. Under some kind of disturbance, these molecular clouds begin to gather into clusters, and then the matter becomes bigger and bigger like a snowball. When gathered to a certain extent, as the hydrogen in the core begins to fuse, the first stars in the universe are born, also known as "third star stars".

Note: the "third star" does not refer to the third generation of stars, but to the first generation! Instead, the third generation of stars is the "first star family star"!

Although we haven't really seen third-family stars so far, we can speculate on what they look like. For the first stars that lack heavy elements, they may grow fat, many of whom are "fat" with more than a hundred times the mass of the sun. Because of the "malnutrition", the element is relatively simple, so the form of fusion reaction inside the star is also relatively primary, it is difficult to generate enough energy to support the large body. Therefore, the lifespan of these big guys is very short, and they may hastily spend their lives in hundreds of thousands of years.

However, after the "roughing" of these primary stars, a small amount of metal elements have appeared in the universe at this time. Many of these metal elements gather near the nuclear sphere at the center of the galaxy, so a second generation of stars containing a small amount of metal elements are born. Soon the universe, which is less than 100 million years old, is dominated by the second generation of stars.

Note: each generation of stars here is only roughly divided according to the content of metal elements, not the strict first or second batch. Because the collapse of molecular clouds is random, each generation of stars is neither born nor died at the same time, and the number of generations of stars is more like what we call "generations".

And the birth of a star is not the same as having a child, it may have no so-called "immediate family". In addition to the raw materials that make up stars, there may also be materials spilled by other stars, including the primitive interstellar material at the beginning of the Big Bang. By the same token, the so-called third-generation stars (that is, the first family stars) like the sun today all come from this source of material. It's just that compared with the second generation, the metal content of the third generation of stars is higher than that of the second generation.

In fact, from the perspective of time, we can also see that the sun should belong to the third generation of stars. Because the lifespan of the first generation of stars is recorded in "ten thousand years", this is almost an instant for the 13.8 billion-year-old universe. So the second generation of stars appeared at almost the same time as the first stars of the "grandparents" on a cosmic scale. Therefore, if the second-generation star were to live to this day, it would at least be an "old man" of ten billion years old. And our sun is not yet 5 billion years old, only a "middle-aged", it can be seen that its "seniority" also belongs to the "grandchildren".

For the third generation of stars, they are already quite small, but small is good, that is, the life span is super long. Especially those tiny red dwarfs, because the fusion reaction is very slow, their lifespan can usually reach hundreds of billions or even trillions of years. As the saying goes, "the world is yours and ours, but in the final analysis it belongs to these grandchildren."

To sum up, there are two problems in looking for the wreckage of the previous generation of the sun: first, it may not have an "immediate family member" at all; second, after 5 billion years, the universe is already in vicissitudes of life. You know, the solar system revolves around the center of the Milky way almost every 200 million years. In other words, since the birth of the sun, it has turned at least a dozen or twenty times, not to mention that the Milky way has experienced various events such as the annexation of dwarf galaxies. It can be seen that finding relatives for the sun is extremely difficult.

Although "biological parents" are hard to find, we can try to find brothers and sisters born with the sun.

Generally speaking, most stars are born in groups in molecular clouds, and our sun is no exception. The story begins 4.6 billion years ago. Somewhere in the Milky way, there was a huge molecular cloud. This molecular cloud may come from the remnants of the previous generation of stars, or it may contain primitive interstellar matter, where stars, large and small, are piling up one after another. Soon, an open star cluster was born.

Unlike a nursing home for stars like a globular cluster, the open cluster is a complete kindergarten. It's just that a few stars grow very fast (massive stars), and their companions are still in small shifts, but they have reached the age of 80.

One day our sun was playing happily with our buddies when a "big man" suddenly exploded. This explosion does not matter. It not only blows the ecliptic plane of the solar system askew, but also makes the orbits of many small objects inside become outrageous. For example, the asteroid Sedna with extremely high orbital eccentricity now has a difference of more than 800 astronomical units between perihelion and aphelion.

The open cluster is already very loose, but after the explosion of a supernova, coupled with the gravitational pull of other molecular clouds around it, the original cluster began to break up. Only about 100 million years later, with the disintegration of the cluster, a looser structure called "star association" emerged.

The Constellation is a group of young stars that have been unbound by gravity but are still moving in the same direction. Because it comes from the previous open star cluster, it is equivalent to this group of children who have graduated from kindergarten and started school. However, the life of the ivory tower is also short, and in less than hundreds of millions of years, these small stars will enter the big society of the universe one by one and begin to wander alone.

Because these stars come from the same molecular cloud, have common characteristics in some chemical elements, and they also share the same direction in earlier movements, and considering that they are not very different in age, perhaps we can find clues of sibling stars from these aspects.

In a paper published in the Astrophysical Journal in 2014, a team of researchers claimed that they may have found the sun's first sibling star, HD 162826.

This star is located in the constellation Perseus and is currently 110 light-years away. This is a late-stage F-type dwarf star, currently slightly larger than the sun and about the same mass as the sun. HD 162826 is currently the most homologous star to the sun, both in terms of chemical composition and orbital dynamics.

Is there a similar planet around such a star of the same origin as the sun? Unfortunately, we haven't observed any planets near it so far. And astronomers speculate that neither hot Jupiter, which is closer, nor gas giants farther away, are likely to appear here. But it is not impossible to have smaller Earth-like planets. In the face of a "sun" in the late stage of evolution, I wonder how the civilization on that planet will feel.

Although now we have only found one brother of the sun, in fact the sun may have far more brothers and sisters than we thought. It was previously estimated that there were about 500 stars born with the sun, but follow-up studies suggest that the number may be an order of magnitude higher, about 2000 to 20000.

However, there are not many red dwarfs of the same size as the sun, and most of them are red dwarfs with a mass of several times the mass of the sun. At present, there are not many ways to analyze the chemical composition of these low-mass M-type dwarfs, so it is difficult to identify whether they are brothers and sisters of the sun.

The good news is that ESA's Gaia mission will play a key role in finding relatives of the sun, as one of its most important goals is to create a three-dimensional map of the Milky way with 1 billion stars.

Because the Gaia telescope takes pictures at a pace of about half a year, it can record the motion data of stars and speculate their past trajectories, making it easy to find stars that have intersected with our sun at a particular time. After that, if it can be identified from the chemical fingerprint, finding those separated "brothers and sisters" may be just around the corner.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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