Research Highlights and News

  Home/Research/Research Highlights and News

Forming planets by pebble accretion: a metallicity gradient emerges

Following our previous research efforts, we have conducted numerical calculations about the thermal evolution of the envelope of pebble-accreting protoplanets. These protoplanets emerge early, when the protoplanetary gas disk is still present. Due to the accretion of solids, their envelope becomes hot, sublimating the infalling pebbles and transforming mm-sized solid particles (“pebbles”) into a metal vapor (e.g, SiO2). This transformation greatly affects the thermodynamical evolution of the protoplanet. For example, planets end up with a small "core" but may still undergo runaway gas accretion due to the high molecular weight and small pressure scale height of the atmosphere.


History of the Solar Nebula from Paleomagnetism

The solar system formed about 4.6 billion years ago. During that time, left-over materials of gas and dust orbited the proto-Sun and formed a disk known as the “solar nebula”. Through a sequence of growth by coagulation and accretion, dust in the solar nebula eventually grow to form our planetary system. The solar nebula is the counterpart of “protoplanetary disks”, which are commonly found around other young stars in the Milky Way. Magnetic fields are known to play a crucial role in the formation, evolution, and dynamics of protoplanetary disks, and hence the processes of planet formation. Currently, attempts to directly measure or infer magnetic field from protoplanetary disks from astronomical observations have been unsuccessful. On the other hand, ancient meteorites have the potential to record the magnetic field in the solar nebular when they formed, which can be deciphered from techniques in the field known as paleomagnetism.


PolarLight in the Orbit for Two Years

On 29 October 2020, the PolarLight X-ray polarimeter has been working in orbit for 2 years. On 29 October 2018, the CubeSat Tongchuan-1 with the PolarLight detector onboard was launched into a Low-Earth orbit from the Jiuquan satellite launching center. On December 18 of that year, the detector was powered on and detected the "first light" event. In March of 2019, after the commissioning phase of the satellite, PolarLight started scientific operations and has since been observing the Crab nebula, Sco X-1, as well as the in-orbit background. After two years, the detector is still working properly, without any performance degradation.


2020 Zhenyi Scholarship awarded to Dr. Xiaochen Zheng

The 2020 Zhenyi Scholarship was held on Oct. 8th. Ms. Tao Fei, the sponsor of the Zhenyi Scholarship, attended the event together with graduate and undergraduate students, postdocs and faculty members of the DoA. Prof. Feng Hua introduced the purpose of establishing the Zhenyi Scholarship. Ms. Tao presented the prize to Dr. Zheng Xiaochen, the winner of this year's Zhenyi Scholarship, for her work on the dynamics of extrasolar planets and determination to pursue a career in astronomy. Afterwards, all participants shared their experiences, especially their perseverance required for female scholars to pursue a research career in the fundamental sciences. Finally, all female scholars of the DoA took a group photo.


Lyα forest as an emerging window into the epoch of reionization

During cosmic reionization (redshift z~8), the intergalactic medium (IGM) is heated by ultraviolet photons originating from stars and galaxies. This extreme heating leaves an imprint in the IGM by injecting the gas with additional thermal energy. The IGM will eventually relax and dissipate the surplus energy, leading to a simple relation between the temperature and the density of the IGM (see, e.g., McQuinn, 2016).


Department of Astronomy welcomes new graduate students

The opening ceremony unveiled a new chapter for the incoming postgraduates of the Department of Astronomy (DoA) on August 26. The DoA welcomed 11 postgraduates this year, 4 females and 7 males, all wearing a specially-designed DoA T-shirt. The meeting was moderated by Hua Feng, the deputy chair of the Department, and was also attended by faculty members Chris Ormel, Tipei Li, Shude Mao, Yi Mao, Dandan Xu, Sharon Wang, and selected senior students.