星际介质中的纳米尘埃
发布时间：2018-09-13 15:59
【摘要】：星际尘埃,作为一种在宇宙中普遍存在的重要成分,在天文学研究中起着重要的作用.星际介质中的尘埃其尺寸分布涵盖从几个埃到几个亚微米的范围.对于有这样大的尺寸差异的星际尘埃,尘埃的热辐射机制差别很大.较大的尘埃颗粒,有比较大的吸收和发射截面,因而其吸收光子的速率和发射的速率也比较大,可以从吸收和发射能量的平衡来得出热平衡温度,并用热平衡温度和黑体辐射来计算其光谱.对于大小为纳米尺度或者更小的尘埃,由于其很小的尺寸,这类尘埃的热容量非常小.当这种尘埃吸收一个与其热容量相当或者更大能量光子的时候,尘埃就会经历一个非常明显的温度涨落:尘埃吸收一个紫外光子瞬间,其温度迅速上升,到达顶点后,由于尚没有外来能量的影响(因吸收截面小,吸收光子几率也非常小),尘埃开始通过热辐射降温,直到吸收另一个光子开始新的循环,这就是单光子加热模型(Single-Photon Heating Model).显然,热平衡和单光子加热是两个明显不同的过程.对于单光子加热,由于尘埃颗粒的温度涨落作用,尘埃不会处于一个稳定的平衡温度状态,因而不能用单一温度来描述其热辐射,必须计算出尘埃在温度涨落过程中的温度分布函数,然后计算其辐射谱.本文主要介绍纳米颗粒在星际空间中的存在证据,单光子加热模型,以及处于温度涨落中纳米颗粒的辐射特征.
[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.
【作者单位】： 北京师范大学天文系;密苏里大学物理与天文学系;
【基金】：国家自然科学基金资助项目(批准号:11173019)
【分类号】：P155.2
，
本文编号：2241652
[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.
【作者单位】： 北京师范大学天文系;密苏里大学物理与天文学系;
【基金】：国家自然科学基金资助项目(批准号:11173019)
【分类号】：P155.2
，
本文编号：2241652
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