Magnetic Braking

One solution to this problem invokes magnetic braking. The material of the disk is following orbits defined by Kepler’s laws. Thus it is orbiting the Sun more slowly than the Sun is rotating. The situation is analogous to the interaction of the material in the Io plasma torus with the rapidly spinning magnetic field of Jupiter. The material in the inner part of the disk is ionized. The Sun’s magnetic field encounters resistance from this plasma as the Sun rotates, slowing down the spin.

This idea has several problems. It doesn’t explain why only stars with low masses exhibit slow rotation, since it is well known that some stars with large masses have strong magnetic fields. A solution to this dilemma would be to postulate that only low-mass stars form with disks, but we now know that disks are not uncommon about young stars with masses greater than the Sun’s. Finally, magnetic braking would transfer angular momentum to the disk and hence to the planets. Yet as we have seen, the problem is not that the planets have too much momentum, but only that the Sun has too little.

8. The Solar Wind: Blowing the Problem Away

A second solution involves the solar wind. Recall that the gases in the outer fringes of the solar atmosphere have enough energy to escape into space, flowing steadily outward through the solar system at speeds of about 400 km/s. The amount of matter lost in this way is a tiny fraction of the Sun’s total mass. Observations of very young stars with small masses like the Sun’s indicate that they generate intense stellar winds shortly after they form. While it is difficult to make an accurate estimate of this effect, it appears sufficient to account for the present slow rotation of the Sun.

An especially appealing aspect of this theory of solar wind braking is its natural explanation of the mass-dependence of stellar rotation. It turns out that only stars with masses comparable to or less than that of the Sun have the proper atmospheric structures to produce steady stellar winds. Hence the same strong wind that ultimately clears residual gas and dust from the disk can slow down the rapidly rotating star that generates it. More massive stars will not produce such winds, so they will continue to exhibit rapid rotation.

Tasks

Task 1. Fill in the gaps in the sentences with the appropriate word from the list.

chemical composition, to dazzle, constellation, to postulate, to occur, to reveal, external, conversion(2), to invoke, internal, ejection, to spawn

1. By means of a study of the typography and the ________ of the paper, they ascertained it to be a fraud.

2. The tests detect genetic markers that _________ whether people share a common ancestor or relative.

3. It proved an ____________ combustion engine could power a vehicle and a human being could control it.

4. Mudpuppies are easily distinguishable by their bushy, red _________ gills, which they grow as larva and never lose.

5. Once again, that marvelous package of scientific instrumentation is free _________ our senses and boggle our minds.

6. Some beta-blockers, however, are also useful in reducing the frequency of migraine attacks and their severity when they _________.

7. He built the only truly global _________ of news, sports, and entertainment properties.

8. The number of indigenous fish was falling, since the floods that induce them __________ were becoming rarer.

9. It is useful to examine the impacts of a monolithic energy ________ strategy using various energy __________ technologies.

10. The term jet propulsion refers to the action produced by a reactor to the ________of matter.

11. One way out of that dilemma is __________ a phenomenon known to biologists as group selection.

12. Used and accurately applied their mental model of the world ___________ a physical explanation for findings.

Task 2. Match the definitions with the terms.

the planetary system, the solar system, chemical composition, angular momentum,

solar nebula, nuclear fusion

1. the identities, and relative numbers, of the elements that make up any particular compound.

2. consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago.

3. the process by which two or more atomic nuclei join together, or " fuse", to form a single heavier nucleus.

4. The rotating flattened cloud of gas and dust from which the sun and the rest of the bodies in the solar system formed, about 4.56 × 109 years ago.

5. a vector quantity that can be used to describe the overall state of a physical system. The angular momentum L of a particle with respect to some point of origin.

6. a set of gravitationally bound non-stellar objects in orbit around a star or star system.

Task 3. Translate the sentences that are underlined in the text into Russian.

Task 4. Give full names to the following elements.

1. CH2OH2 –

2. CH2O –

3. HCN –

4. CO2 –

5. OH –

6. H2O –

Task 5. Translate the sentences into English, using the active vocabulary above.

1. Результаты исследования, опубликованные в этом журнале, обнаружили недостатки метода, применяемого ранее.

2. Его возражения только усилили убеждение оппонентов.

3. Внутренние механизмы организма способны как уберечь его от распространения раковых клеток, так и ускорить его.

4. Необходимо избавиться от всего, что способствует размножению плесени, поскольку она негативно повлияет на ход эксперимента.

5. Даже развитые страны еще не готовы к переходу от крупномасштабного использования полезных ископаемых к использованию водорода как основного источника энергии.

6. В неизмененном состоянии эта вакцина не содержит загрязняющих кровь веществ.

7. Культурное и этническое разнообразие ценится выше в демократических странах.

8. Применяя новые материалы при конструировании солнечных батарей, можно утверждать, что они поглощают теперь больше солнечного света и преобразуют его в энергию эффективнее.

9. При современном изобилии информации, ученые сочли возможным сослаться на ранее не изученное явление “групповой селекции”.

10. Последнее время многие ученые придерживаются противоположных взглядов на данную проблему, постоянно подвергая сомнению ее правильность.