【摘要】：星際塵埃,作為一種在宇宙中普遍存在的重要成分,在天文學(xué)研究中起著重要的作用.星際介質(zhì)中的塵埃其尺寸分布涵蓋從幾個(gè)埃到幾個(gè)亞微米的范圍.對(duì)于有這樣大的尺寸差異的星際塵埃,塵埃的熱輻射機(jī)制差別很大.較大的塵埃顆粒,有比較大的吸收和發(fā)射截面,因而其吸收光子的速率和發(fā)射的速率也比較大,可以從吸收和發(fā)射能量的平衡來(lái)得出熱平衡溫度,并用熱平衡溫度和黑體輻射來(lái)計(jì)算其光譜.對(duì)于大小為納米尺度或者更小的塵埃,由于其很小的尺寸,這類塵埃的熱容量非常小.當(dāng)這種塵埃吸收一個(gè)與其熱容量相當(dāng)或者更大能量光子的時(shí)候,塵埃就會(huì)經(jīng)歷一個(gè)非常明顯的溫度漲落:塵埃吸收一個(gè)紫外光子瞬間,其溫度迅速上升,到達(dá)頂點(diǎn)后,由于尚沒有外來(lái)能量的影響(因吸收截面小,吸收光子幾率也非常小),塵埃開始通過熱輻射降溫,直到吸收另一個(gè)光子開始新的循環(huán),這就是單光子加熱模型(Single-Photon Heating Model).顯然,熱平衡和單光子加熱是兩個(gè)明顯不同的過程.對(duì)于單光子加熱,由于塵埃顆粒的溫度漲落作用,塵埃不會(huì)處于一個(gè)穩(wěn)定的平衡溫度狀態(tài),因而不能用單一溫度來(lái)描述其熱輻射,必須計(jì)算出塵埃在溫度漲落過程中的溫度分布函數(shù),然后計(jì)算其輻射譜.本文主要介紹納米顆粒在星際空間中的存在證據(jù),單光子加熱模型,以及處于溫度漲落中納米顆粒的輻射特征.
[Abstract]:Interstellar dust, as an important component in the universe, plays an important role in astronomical research. The size distribution of dust in interstellar media ranges from several E to several sub-microns. For interstellar dust with such large size differences, the thermal radiation mechanism of dust varies greatly. The larger dust particles have relatively large absorption and emission cross sections, so the rate of absorption and emission of photons is also relatively large. The heat equilibrium temperature can be derived from the equilibrium of absorption and emission energy. The spectra are calculated by heat equilibrium temperature and blackbody radiation. For nanoscale or smaller dust, the heat capacity of such dust is very small because of its small size. When the dust absorbs a photon of energy equal to its heat capacity or greater, the dust experiences a very obvious temperature fluctuation: the dust absorbs an ultraviolet photon, and its temperature rises rapidly and reaches its peak. Since there is no influence of external energy (because of the small absorption cross section, the probability of absorbing photons is also very small), dust begins to cool through thermal radiation until another photon is absorbed into a new cycle, which is called the single photon heating model (Single-Photon Heating Model). Obviously, thermal equilibrium and single photon heating are two distinct processes. For single-photon heating, due to the temperature fluctuation of dust particles, the dust will not be in a stable equilibrium temperature state, so it is not possible to describe its thermal radiation by a single temperature. The temperature distribution function of dust in the process of temperature fluctuation must be calculated, and then the radiation spectrum of dust must be calculated. This paper mainly introduces the evidence of the existence of nanoparticles in interstellar space, the single photon heating model, and the radiation characteristics of nanoparticles in temperature fluctuations.
【作者單位】： 北京師范大學(xué)天文系;密蘇里大學(xué)物理與天文學(xué)系;
【基金】：國(guó)家自然科學(xué)基金資助項(xiàng)目(批準(zhǔn)號(hào):11173019)
【分類號(hào)】：P155.2
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本文編號(hào)：2241652