Science News内容：

题目：MIT astronomers find the smallest asteroids ever detected in the main belt

摘要：Asteroid discoveries are essential for planetary-defense efforts aiming to prevent impacts with Earth, including the more frequent megaton explosions from decameter impactors. While large asteroids (≥100 km) have remained in the main belt since their formation, small asteroids are commonly transported to the near-Earth object (NEO) population. However, due to the lack of direct observational constraints, their size-frequency distribution —which informs our understanding of the NEOs and the delivery of meteorite samples to Earth—varies significantly among models. Here, we report 138 detections of the smallest asteroids (⪆ 10 m) ever observed in the main belt, which were enabled by JWST’s infrared capabilities covering the asteroids’ emission peaks and synthetic tracking techniques. 

报告人：李路子豪（紫台研究生） 

Journal club主报告内容：

题目：Gravitational lensing in the strong field limit

摘要：We provide an analytic method to discriminate among different types of black holes on the grounds of their strong field gravitational lensing properties. We expand the deflection angle of the photon in the neighborhood of complete capture, defining a strong field limit, in opposition to the standard weak field limit. This expansion is worked out for a completely generic spherically symmetric spacetime, without any reference to the field equations and just assuming that the light ray follows the geodesics equation. We prove that the deflection angle always diverges logarithmically when the minimum impact parameter is reached. We apply this general formalism to Schwarzschild, Reissner-Nordstro¨m, and Janis-Newman-Winicour black holes. We then compare the coefficients characterizing these metrics and find that different collapsed objects are characterized by different strong field limits. The strong field limit coefficients are directly connected to the observables, such as the position and the magnification of the relativistic images. As a concrete example, we consider the black hole at the center of our galaxy and estimate the optical resolution needed to investigate its strong field behavior through its relativistic images.

报告人：曹定龙（紫台研究生）

时间：2024年12月24日星期二12:15

地点：紫台3-402