Optics of Interstellar Dust: New Methods and Applications

天文学家主要依靠对电磁辐射（光）的观测来研究从恒星到星系再到类星体的物体。星际空间中的尘埃颗粒吸收并散射了这种光。同样的尘埃颗粒也以长（红外）波长辐射，这种红外辐射是可以观察到的。尘埃颗粒影响着从x射线到亚毫米波长的天体的外观。为了理解我们所看到的，我们必须知道尘埃颗粒的散射和吸收特性是如何取决于它们的组成、大小和形状的。此外，光的吸收和散射会对晶粒产生强大的力和扭矩。例如，来自太阳的光可以排斥接近太阳系的尘埃颗粒。阳光也会使不规则形状的颗粒旋转得足够快，以至于离心应力会破坏颗粒。由于尘埃颗粒形状不规则，计算散射和吸收是一个具有挑战性的数学问题。研究者的目标是改进计算复杂形状颗粒散射和吸收的方法。一个重点将放在与辐射波长（如红外线）相比，颗粒本身很小的重要情况上。第二个重点将是开发和实现更快的方法来计算作用在晶粒上的力和扭矩。这些改进的方法将在研究者开发和支持的公开可用的开源代码DDSCAT的新版本中实现。新版本的DDSCAT将用于计算散射和吸收截面的“库”。这将用于晶粒形状和组成的样品，以及宽范围的波长。该图书馆将对其他研究人员在线开放。该库将包括计算散射和吸收所需的横截面，以及计算作用在颗粒上的力和扭矩所需的数据。横截面库将用于开发和测试星际尘埃种群的模型。一个流行的模型设想典型的星际颗粒是松散的聚集体。该库将用于检验该模型是否与现有观测数据兼容。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Astronomers rely primarily on observations of electromagnetic radiation -- light -- to study objects ranging from stars to galaxies to quasars. Dust grains in interstellar space absorb and scatter this light. The same dust grains also radiate at long (infrared) wavelengths, and this infrared radiation is observable. Dust grains affect the appearance of astronomical objects from X-ray to sub-millimeter wavelengths.To understand what we see, we must know how the scattering and absorption properties of dust grains depend on their composition, size, and shape. In addition, absorption and scattering of light can produce strong forces and torques on grains. For example, light from our Sun can repel dust grains approaching the solar system. Sunlight can also cause grains with irregular shapes to spin fast enough for centrifugal stresses to disrupt the grain.Because dust grains have irregular shapes, calculating scattering and absorption is a challenging mathematical problem. The investigator aims to improve methods for computing scattering and absorption for grains with complicated shapes. One emphasis will be on the important case where the grain itself is small compared to the wavelength of the radiation (as in the infrared). A second emphasis will be on developing and implementing much faster methods for computing the forces and torques acting on the grain.These improved methods will be implemented in new versions of the publicly-available open-source code DDSCAT which the investigator developed and supports. The new version of DDSCAT will be used to compute a "library" of scattering and absorption cross sections. This will be done for a sample of grain shapes and compositions, and for a wide range of wavelengths. The library will be available on-line to other researchers. The library will include cross sections needed to calculate scattering and absorption, as well as data needed to calculate forces and torques acting on grains.The cross-section library will be used to develop and test models for the interstellar dust population. One popular model envisions typical interstellar grains as loose aggregates. The library will be used to see whether this model is compatible with existing observational data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.