2018-02-14
202
I. First reading of the “Ancient Stardust in the Laboratory”.
1.Read the text quickly and try to understand what it is about and what information in the field Ancient Stardust is known to you.
2.Write down space terms, known to you, in Russian
3.Write a list of the names of the scientists and laboratories that took part in the research of stardust.
4.Find in the text: a) the sentence about the age of the dust.
b) the sentences about the study of anomalies in meteorites.
II. Scanning Reading
1. Read the text again. Find in the text:
a) the sentence about the most compelling evidence for the AGB origin of most grains.
b) the sentence about the kinds of grain which have not been identified in the presolar grain population.
2.Pick out the galaxy terms you do not know from the text.Refer to a dictionary if necessary.
III. Vocabulary and word study
A Vocabulary
| grains of dust | крупинки пыли |
| decay n | распад |
| treatment n | зд. изучение, исследование |
| body n | зд. комплекс, массив |
| supernova n | сверхновая звезда |
| abundance n | распространённость, изобилие |
| spallation n [spo:lei∫n] | раскалывание, расщепление |
| tenet n [ti:nit] | догмат, принцип, доктрина |
| spherule n ['sferju:l] ['sfiəru:l] | шарик, небольшой шар |
| extinct adj | потухший |
| noble gas | инертный газ |
| to enrich | обогащать |
| host | основа |
| to buttress v | поддерживать |
| a separate n | отдельная часть |
| diamond n | алмаз |
| primitive adj | первозданный, простой, грубый |
| circumsttellar adj | околозвёздный |
| to dredge up v | углублять, драгировать, ловить |
| to reconcile v | примерять, согласовывать |
| to vindicate v | подтверждать, доказать |
| formidable adj | внушительный, значительный, труднопреодолимый |
| to infer v | подразумевать, означать |
| noncommittal adj | уклончивый |
| to blust appart | взрывать, разрушать |
| preaccretionary adj | ранее разросшийся, увеличенный |
| in situ | на своём месте |
| nebula n | галактическая туманность |
| mainstream n | основной поток |
| blob n | капля, сгусток |
| outflow n | отток, истечение |
| to eject | выбрасывать, выталкивать, выносить |
| exotic adj | необычный |
| presolar | досолнечный, т.е. до образования солнца |
| remnant n | след, остаток |
| circumstellar adj [,səkəm'stelə] | околозвёздный |
| outgrowth n | зд. результат, следствие |
| insight n | проницательность, интуиция, понимание |
| to tailor v | приспособить, подогнать |
В Word Study
1. Find the related verbs in the text
Determination indication erosion
Identification orign existence
Integration formation condensation
Measurement prediction ejection
Enrichment estimation provision
2 .Find the related nouns in the text
To explode to vary to enrich
To distribute to include to evolve
To measure to inform to realize
To contribute to develop to conclude
To form to add to compose
To contaminate
3. Find the related adjectives in the text
Chemistry molecule star
Theory composition nucleus
Carbon isotope astronomy
Type symmetry difference
1. Improve your vocabulary. Make the following sentences complete by translating the words and phrases in brackets.
a) How can one identify (пылинку) (в качестве) ancient (звёздной пыли).
в) Indeed, this is probably the only way ancient stardust can be distinguished from (твёрдых тел) that formed within (Солнечной системы).
c) And other (аномалии) could be carried by (остатками) of chemically processed (материал) from (межзвёздных малекулярных облаков).
d) Each species of (крупинок) provides (новую информацию) that must be integrated into the existing body of (астрофизических знаний).
e) With this (открытие), the laboratory study of individual (крупинок звёздной пыли) was born.
f) An interesting out growth of these (исследований) is the (понимание) that the (соединение кислорода) can be used to (определить) the (возраст) of the Galaxy.
e) Presolar (пылинки) provide a new way to (изучать) (различные процессы) in the early (Солнечная система).
ANCIENT STARDUST IN THE
LABORATORY
Abridged
As it collapsed to form the Solar System, material in the solar nebula was churned up and homogenized. But not everything was lost in the mix…
Thomas J.Bernatowicz and Robert M.Walker
1 Amazingly, individual grains of dust from stars that existed before the Sun was born have made their way to Earth in meteorites. When subjected to a battery of cutting-edge laboratory techniques, these tiny grains provide thrilling new insights into such topics as the dynamics of supernova explosions, the age and chemical evolution of the Galaxy, fundamental nuclear physics and processes in the outer envelopes of stars. The path from dust grain to astrophysical insight is the subject of this article.
2 For the last half century, several key ideas have dominated how we think nuclides were formed and then distributed in nature. In the 1950s, Hans Suess and Harold Urey showed that it is possible to determine the average abundances of elements and isotopes in the Solar System from laboratory measurements of primitive meteorites. These meteoritic abundances turned out to be similar to those measured spectroscopically in the Sun. It was also realized that very few nuclides could have been produced in an initial "big bang" and that most element synthesis is in fact the result of nuclear reactions in stars. And ever since the publication of the two classic papers in 1957 we have known that the abundances of elements and isotopes in the Solar System must reflect contributions from many different types of stars.
3 Until recently, it was believed that the contributions of individual stars to the solar mix could not be determined directly. This belief followed from the fact that closely similar isotopic ratios were measured in a wide variety of terrestrial and extraterrestrial samples, suggesting that all presolar solids had been vaporized when the Solar System formed. Complete isotopic homogenization was the result. We now know this is not quite true. Surprisingly, some individual grains of Stardust survived the formation of the Solar System and can be isolated from primitive meteorites.
4 How can one identify a grain as ancient stardust? Because the solar isotopic compositions are the grand averages of contributions from many individual stars, any grain of surviving stardust should generally have isotopic compositions in one or more elements that are markedly different from the solar values. Indeed, this is probably the only way ancient stardust can be distinguished from solids that formed within the Solar System.
5 Identifying individual stardust grains is just one aspect of the larger study of isotopic anomalies in meteorites (an anomaly being defined as a significant deviation from a well-determined solar isotopic ratio). In themselves, isotopic anomalies do not necessarily imply that their carriers are stardust, for most anomalies are actually quite small and arise from well-understood processes For example, there are anomalies due to nuclear spallation reactions in materials exposed to high-energy cosmic rays in space. And other anomalies could be carried by remnants of chemically processed material from interstellar molecular clouds. However, here we are concerned only with isotopic anomalies that are so huge that they constitute clear evidence that the grains carrying them are samples of ancient stardust—that is, dust that formed around stars other than our Sun before the Solar System was born 4.6 billion years (Ga) ago.
6 The variations in isotopic composition among individual presolar grains demonstrate that many stars of several different types have contributed to the Solar System mix, beautifully confirming the basic tenets of nucleosynthesis, as the theory of element formation is known.
7 Presolar grains identified so far include aluminum oxide (A12O3), graphite spherules, silicon carbide (SiC), silicon nitride and a variety of metal carbides found as small inclusions in larger presolar grains. Each species of grain provides new information that must be integrated into the existing body of astrophysical knowledge. This eclectic process requires the work and insights of astronomers, theoretical astrophysicists and laboratory scientists.
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FIGURE 1. STARDUST IN THE LABORATORY, as evident in electron micrographs, a: A presolar silicon carbide crystal from the Murchison meteorite. The 12C / 13C ratio of this crystal is 39—radically different from the solar value of 89, which tags it as a grain that originated outside the Solar System. This crystal most likely condensed in the expanding atmosphere of a star on the asymptotic giant branch. It measures about 4µ m across. (Photo courtesy of Sachiko Amari.) b: A 70 nm thick section of a presolar graphite spherule. The crystal in the center of the spherule is titanium carbide, a refractory mineral that formed before the graphite and served as a nucleation center for its growth. The dark, radial spokes in the image are an electron diffraction effect; in reality, the graphite layers are concentric.
