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

Thanks CTOnews.com netizen Hua Ke high achiever's clue delivery! The ancient Greek philosopher Aristotle once believed that time had no beginning and no end, and that our earth was supposed to be infinitely old; ancient Indian scholars believed that the universe had a beginning and an end, but it was repeated over and over again. This round of the earth should have existed for nearly 2 billion years; and some medieval theologians took out the Bible, and after some deliberation, they thought that the age of the earth should only be a few thousand years. Thus it can be seen that without a set of scientific methods, people can not reach a consensus on the age of the earth, let alone study the universe.

Later, scientists began to look for clues from nature and came up with a variety of numerical values. Nowadays, with the continuous improvement of measurement methods, people's estimation of the age of the earth is becoming more and more accurate. According to the measurement of radioactive elements, the age of the earth should now be about 4.54 billion years old.

Assuming that the earth was born with the sun, it can be thought that the sun today should be about the same age. When this age, together with data from the sun, is incorporated into the theory and modeled, we begin to have a preliminary understanding of celestial bodies such as stars. From then on, even when facing a star several light-years away, we can calculate its approximate age based on the theoretical model. Once we know the age of the star, we will know the age of the planets around it, which is how we know the age of exoplanets at present.

Last time we introduced an exoplanet in an ancient globular cluster, which, along with its parent star, was born at dawn 1 billion years after the Big Bang and became the oldest planet ever observed at the age of nearly 12.8 billion. The oldest planet is tens of billions of years old. How young is the youngest planet?

To find the youngest planet, its host star must be young enough. As mentioned before, many of the older stars are located in the "nursing homes" of stars such as globular clusters, and if you want to find young stars, you must have a look in the star's "kindergarten" open cluster.

However, it is too much for the open cluster to say that it is a "kindergarten". In fact, it can only be regarded as the cradle of stars at best. Under the action of internal dynamics and external tidal forces, most of the open clusters will soon be disintegrated. Although the cluster was disintegrated, most of the star babies inside remained in formation, and the structure at this time was called the Star Association. For those associations that are mainly composed of O-type and B-type high-mass stars, they are called "OB associations".

In 2016, through the Kepler telescope, astronomers discovered a young star, K2-33, in the Scorpio-Centaur Association, the closest OB association to Earth. Although it is located in the OB Association, K2-33 is not very massive (only half the sun) and can be regarded as an M-type dwarf star.

For many of the small stars here, their protoplanetary disk has dissipated. The absence of the placenta means that they may have successfully "delivered" their own planetary children. Sure enough, through the transit method, people really found a planet the size of Neptune-K2-33b around K2-33.

In general, the smaller the star, the smaller the placenta, so the child is usually not too large. But this star, although it is not big, the child is not small. It is a giant planet with 3.7 times the mass of Jupiter and 5 times the radius of the Earth.

And the giant planet is still very close to its parent star, with only 0.04 astronomical units, almost 1 / 10 of Mercury to the sun. At this close range, the planet is usually the size of Earth. So this indicates that although the planet has been "born", but a little "baby fat", the follow-up may have to go through a "weight loss" stage. For example, under the action of the stellar wind, its outer atmosphere will be gradually blown away.

According to the standard model of planet formation, if all aspects of such planets are to be "mature", they will not be able to come down in tens of millions of years. According to the model, the age of the planet is only about 9.3 million years old. In the eyes of the 4.5 billion-year-old "old comrade" of the earth, it is no longer a "young man", but a "newborn" before the full moon.

A 9.3 million-year-old "newborn" is somewhat understandable, but in the face of a 2 million-year-old "premature baby", how should scientists deal with it?

Taurus T Star (TTS) is a variable star that has not yet entered the main sequence star stage and is in the process of forming, usually less than 10 million years old. Taurus V830 is such a pre-main sequence star with a history of only 2 million years. The star is about the same mass as the sun, but its radius is twice that of the sun, so it is speculated that it is still in the inward contraction phase. But unlike most Taurus T stars, the Taurus V830 does not seem to have an obvious circumstellar disk. The lack of a protoplanetary disk means that the planets here may have been born before the stars.

Sure enough, in the same year that K2-33b was discovered, through the radial velocity method, astronomers confirmed that Taurus V830b did exist near Taurus V830. Like K2-33b, Taurus V830b is also a large planet very close to the star, 0.057 astronomical units from the star and 0.77 times the mass of Jupiter.

For this kind of planet which is close to the star and is also very large, it is called "hot Jupiter".

Although many hot Jupiter have been found around mature sun-like stars, hot Jupiter around such a young star is rare. One is because the magnetic field of young stars is very strong, which interferes with the signal of radial velocity, making it difficult to observe; the other is that many hot Jupiter were born relatively far away from the star, and they later migrated to the star. this migration usually takes hundreds of millions of years, which is not enough time for newly formed planets. And this kind of migration generally needs the assistance of companion stars or other planets, which may not be feasible by the planets alone.

Can't people just form in front of the stars? This is usually very difficult. Because the temperature near the star is high, it is difficult for matter to remain solid, and the solar wind blows so hard. as one can imagine. And as a planet, the gravity is extremely limited, you can't beat other people's stars for resources, and you don't have that ability, you know. Why are the water, gold, earth and fire of the inner solar system all rocky planets?

In addition, even if you try your best to grab a lot of resources by some means, you have to worry about whether you will fall into the "trap" of the stars, and don't look back and be swallowed by others. After all, "often walk by the river, there are no wet shoes", in such a large source of gravity, the slightest carelessness may be doomed.

So how on earth do these "giant babies" appear in front of stars?

First of all, of course, we do not rule out the possibility of forming directly in the current position. Although it is difficult to obtain resources, the magnetic field of the peristellar disk may play a role in preventing planets from falling into stars. In addition, planets may have other mechanisms that enable them to complete their migration in a short period of time, such as interactions with the original planetary disk that may spontaneously lead to their orbital migration. Of course, these are only preliminary guesses, and research in this area is still in progress.

In short, the study of hot Jupiter, especially around young stars, can not only help improve the theory of planetary formation, but also a key link in our understanding of how the entire planetary system, including the solar system, is formed.

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

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