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Stellar Anatomy and Longevity Help

By — McGraw-Hill Professional
Updated on Sep 17, 2011

Stellar Anatomy—Model Stars

It is safe to say that no human being will ever travel inside a star to find out what the interior is like. Conditions inside stars are too hostile for any kind of direct observation or exploration; space ships would be vaporized on reaching the surface, if not before. The science-fiction story “Icarus and Daedalus,” written by Russian author Henrik Altov, portrays a hypothetical journey through the center of the Sun. However, such stories will always remain fiction.

Model Stars

Astronomers have deduced certain things about the interiors of stars, including the Sun, just as they have been able to gather ideas about the interiors of the planets, including the Earth. Different types of stars have different internal structures. We also know that different types of stars have much different “atmospheres.” The “atmosphere” surrounding a star can extend outward for millions of kilometers and is called the corona .

Computers have been used to construct model stars using programs that simulate events believed to take place in the depths of these fusion furnaces. Known physical laws are applied to denote what happens inside a star with a given mass and material composition. Stars are considered to have concentric layers or “shells,” each with a certain temperature, mass, and combination of elements. The whole star is “constructed” by putting the shells together. This can be done outward from the center toward the surface and then to the corona or inward from the corona to the surface and ultimately to the center. Sometimes, when the two modeling schemes (inside-out versus outside-in) are both applied to objects having the same mass and material composition, the results are different.

In the depths of a large main-sequence star such as a blue supergiant, radiation and convection are believed to be mutually responsible for the transfer of energy from the core of the star into space. Near the surface, radiation predominates. Near the center, convection is thought to play a more important role because the matter deep inside stars is so dense that it is opaque to radiation. This model of a large star is shown in Fig. 13-5 a . In a much less massive main-sequence star, the reverse is believed to be the case. A red-dwarf star apparently has a convective outer region and a more transparent core. Radiation should predominate deep inside such a star. This model of a red dwarf is shown in Fig. 13-5 b .

Stars and Nebulae Stellar Anatomy And
Longevity Model Stars

Figure 13-5. At A , simplified model of the interior of a large main-sequence star such as a blue supergiant. At B , a model of a small main-sequence star such as a red dwarf.

Both these models are largely speculative. Computers can work only with the data that they get, and these data are based on educated guesswork. Nature is not a computer program. We can’t be sure that the models we invent are perfect representations of what really goes on in the Universe. In fact, people ought to know by now, after decades of working with computers, that there are always some differences between the “mind” of nature and the “mind” of a computer program! As observational techniques improve and computers become more enlightened about nature, star modeling should get better and better. We’ll never know for sure, however, what the inside of a star is like unless and until we can send some sort of probe down inside one. The Sun is the logical candidate for a first try, but no one has yet figured out how a navigable space vessel could be designed to survive the extreme temperature and pressure.

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