本帖最後由 iheby 於 2017-8-29 01:16 編輯
雙黑洞合併下原初黑洞能成為暗物質理論研究 @香港大學物理系
Seminar of RPg Student:- Could Primordial Black Holes Be Dark Matter Theoretical Study on the Binary Merger Scenario
Although Dark Matter (DM) has been widely accepted as constituting around a quarter of the energy-mass content of the universe, the actual form of DM has not been resolved. While proposed particle DM candidates, such as Weak Interacting Massive Particle (WIMP), have been evading detection, the other candidate, primordial black holes (PBHs), has gained popularity kindled by the recent gravitational wave (GW) detection by the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). Two of the three confirmed detections in 2015 and 2017 feature binary black hole (BH) components of mass around 30 solar mass, which is unexpected for stellar BHs formed from dying stars, which usually have mass on the order of 1 solar mass. PBHs, on the other hand, are formed from collapsed density fluctuations in the infant days of the universe, thus have broader mass range, suggesting itself as the possible source of the GW signals. Then it becomes very intriguing why these heavy PBHs are so frequently detected in GW. One possibility is that PBH might constitute some or all of DM. This research project would try to explore such possibility by investigating the binary BH merger scenario, the specific process that offered us the inspiration.
時間：2017.08.29(二) 13:15
地點：香港大學 莊月明物理樓522室
講者：Yuan GAO (香港大學)
語言：英語
免費會議，歡迎參加
脈衝星的光譜變化研究 @香港大學物理系
Seminar of RPg Student:- Study Spectral Variations of Glitching Pulsars
Pulsars are highly magnetized rotating neutron stars and radiate beams of emission that are observed as pulses when they sweep across the Earth. Their signature pulse shapes are so stable that high-precision studies of their rotation are possible. Often, pulsar timing can be predicted with a very simple model over many years with an accuracy of a few microseconds, or better. This accuracy provides us great chance to detect and measure very small perturbations embedded in the normal rotation of the star, and further extract information about processes inside and outside the pulsar. The differences of predicted arrival times of pulses and actual arrival times are known as pulsar timing residuals. If the timing model is perfect, timing residuals would be dominated by random measurement errors. Most common feature observed in the timing residuals is spin-down irregularities. Glitch as a main type of timing irregularity is characterized by a sudden increase in rotation rate followed by a period of relaxation, and mostly identified in the radio emission. Although glitches are very common in pulsars, a clear interpretation of this phenomenon is still missing. Here we choose several gamma-ray pulsars and analyze their high-energy emission before and after glitches. Through a comparison of flux, spectrum and pulse shape, we try to discuss the possible scenario of glitch.
時間：2017.08.29(二) 14:30
地點：香港大學 莊月明物理樓518室
講者：Jun TIAN (香港大學)
語言：英語
免費會議，歡迎參加
冷遠的火星形成 @香港大學物理系及地球科學系
Seminar:- The Cool and Distant Formation of Mars
Bulk elemental and isotopic data for martian meteorites demonstrate that key aspects of Mars’ composition are markedly different from that of Earth. This suggests that Mars formed outside of the terrestrial feeding zone. It is therefore probable that Mars always remained significantly farther from the Sun than Earth; its growth was stunted early and its mass remained relatively low. Here we show a robust dynamical pathway that forms and keeps Mars outside of Earth’s accretion zone while at the same time accounting for strict age and compositional constraints, and mass differences. This scenario suggests that Mars’ volatile budget is different from Earth’s and predicts that Venus formed close enough to our planet that it is expected to have similar composition, including the oxygen isotopes.
時間：2017.08.29(二) 16:00
地點：香港大學 莊月明物理樓522室
講者：Prof. Ramon Brasser (東京工業大學 地球生命研究所)
語言：英語
免費會議，歡迎參加
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