The protoplanetary disk is the dense gas surrounding the newly formed young stars (such as Taurus T), because the gas will fall from the inside of the diskfixed starSurface, so it can be regarded as aAccretion disk。However, this process cannot be confused with accretion during star formation.
Protoplanetary disk Proplyd or Protoplanetary DiscTaurus T Star）The dense gas surrounding the outside can be regarded as an accretion disk because it will fall from the inside of the disk to the surface of the star.However, this process cannot be confused with accretion during star formation.
Many newly formed stars are surrounded by a structure called "protoplanetary disk", which contains all the materials that will form the future star system.The temperature and size of the protoplanetary disk surrounding Taurus T are different from those around the binary star.The radius of the original planetary disk can reach 1000Astronomical unit, but the temperature is not high, and the temperature at their innermost side is only 1000K, and oftenJetWith.
Typical protoplanetary disks come from mainly hydrogen moleculesMolecular cloud。When the molecular cloud reaches the critical mass or density, it will collapse due to its own gravity.When the cloud begins to collapse, it can be calledSolar nebulaThe density will become higher, and the molecules originally moving randomly in the cloud will also show the average net angular momentum movement direction of the nebula. The conservation of angular momentum will cause the nebula to shrink while the rotation speed will also increase.This rotation also causes the nebula to flatten, forming a disk like an Italian pancake.About 100000 years after the collapse, when the temperature of the star's surface is the same as that of a star of the same mass in the main sequence belt, the star will become visible, just like Taurus T.The gas in the accretion disk will continue to fall into the stars in the next ten million years before the disk disappears.The disk surface may beStellar windBlow off, or just because after accretion, simply stop radiation and end.The oldest protoplanetary disk discovered has existed for 25 million years.
solar systemThe nebula hypothesis describes how the protoplanetary disk developed intoPlanetary system。The dust particles and particles on the disk that are interacted by static electricity and gravity make them becomeStar Child。This process involves competing stellar winds that blow gas away, accumulating gas and pulling matter into the center of Taurus T.
In our Milky Way, protoplanetary disks around some young stars have been observed.The first is the painting frame β discovered in 1984, and the latest isHubble Space TelescopeFound onOrion nebula The original astrolabe being formed inside.
Astronomers are already in the constellation Lyra, a star not far from the sunVega, North CoronaAlphecca , and Southern FishBeiluo SchoolThe discovery of a large number of protoplanetary materials may already be protoplanetary itself.
Including Zhinu and Beiluo SchoolBeihe IICommon moving star clusters are identified.Using the Hibaku satellite data, it is estimated that the age of the Beihe 2 star cluster is about 200 million years (with an error of about 100 million years), which shows that the remnants of Vega and Beiluoshimen observed in infrared light may have become planetesimals, not just protoplanetary disks.Hubble Space TelescopeWe have successfully observed the protoplanetary chart of Fomalhaut and confirmed the conjecture.
The "protoplanetary disk" can form potential planets, asteroids and other celestial bodies. However, how this transformation takes place has been a mystery for scientists until they mastered the "turbulent" motion of the matter in it."Turbulence" motion is regarded by some people as the last great problem in classical physics.
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By understanding the turbulence in the "protoplanetary disk", the research team of American scientists has established a more accurate model to simulate the evolution of star systems.
The first challenge for scientists is to establish a correct model for computer simulation. Jake Simon, a scientist at the University of Colorado, said: "Our numerical simulation usually uses a very special model, that is, the density and temperature change with the distance from the star.In addition, we must also consider the structure and strength of the magnetic field in the protoplanetary disk, as well as the ionization structure in it. For example, we must find out where there is enough temperature, or where there is a strong radiation source that can knock off the electrons in molecules and atoms to produce positively charged ions.ionizationThe structure is particularly important because the turbulence in the ionized protoplanetary disk will be more vigorous.
The second challenge is how to deal with the technical details of computer simulation.Jake Simon said: "In some regions, the electrons and magnetic fields are firmly combined, while the ions are not, which will lead to a phenomenon called‘Hall effect’Our numerical simulation cannot accurately capture this effect. "[1]
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The protoplanetary disk is a gas disk surrounded by young stars and composed of relatively high density gas and dust.The protoplanetary disk forms simultaneously with young stars during the collapse of the molecular cloud and rotates around the stars.The radius of the protoplanetary disk can reach 1000 AU (astronomical unit), which isPlanetary systemThe birthplace of.The protoplanetary disk is mainly composed of gas and contains a small amount of dust.Although the mass ratio of dust in the protoplanetary disk is very low, it is the main role of radiation transfer in the protoplanetary disk and plays a vital role in the evolution of the protoplanetary disk.
HL Tau is a young star 140 pc away from the Earth. Because there is a protoplanetary disk around it, the HL Tau system has always been a hot spot in millimeter wave astronomical observation.In 2014, ALMA released the scientific test observation results (figure) for the HL Tau system, indicating that there are multiple light and dark bands in the protoplanetary disk of the system.This observation result is one of the major discoveries of the international astronomical community in 2014, and has aroused widespread public concern.This is the first time that astronomers have obtained a high-resolution image of a protoplanetary disk (with a resolution of~3.5 AU). The structural characteristics given by it are of great significance for studying the formation and evolution of planetary systems, because the planetary system of our solar system was born in a protoplanetary disk similar to the HL Tau system.More importantly, the light dark interlaced bands in the HL Tau system and theJupiter like planet(Jupiter, for example) The gap opened in the gas disk matches.What are these observed light and dark bands, and how do they form?
The explanation of the origin of the bright and dark rings in the HL Tau protoplanetary disk can be mainly divided into two categories: the first category attempts to start from the physical environment in the protoplanetary disk, such as Rossby wave ability, zonal flow, condensation of different substances at different temperatures and other mechanisms.The second type of explanation is caused by the interaction of planets with gas disks and dust disks, that is, the observed dark stripes are the observational evidence of the empty belts opened by giant planets in the disk in the theory of planetary formation.
In this study, the researchers first carried out dozens of numerical simulation calculations based on the model of the interaction between planets, gas and dust in the protoplanetary disk, and calculated the observation images corresponding to different model parameters in consideration of the radiation transfer process, and finally gave a group of results of the best fitting ALMA observation data (figure).This work shows that three planets at 13.1, 33.0 and 68.6 AU with masses of 0.35, 0.17 and 0.26 Jupiter can obtain millimeter wave images that are very consistent with the ALMA observation results.According to the observation results of ALMA, researchers have limited the spectral index and dust size in the HL Tau protoplanetary disk.It is shown that the dark streaks observed belong to real optical thin empty bands, and these empty bands exist simultaneously in the gas disk and the dust disk.The research results reveal that the interaction between planets and protoplanetary disks is the cause of these light dark interlaced ring features.This work is not only helpful for people to understand the evolution of protoplanetary disks and the process of planet formation in the HL Tau system, but also has important scientific significance for understanding the origin and evolution of our solar system[2]。
