Time：2023/07/28 (Fri.) 12:10
Place：
4F Lecture Hall, Cosmology Hall, NTU
&
Webex online (Meeting number：2558 004 8376 / Password：TG23 (8423 from phones and video systems))

Title：Exploring Extragalactic SETI and the Role of the MeerKAT Telescope
Speaker：Yuri Uno (National Chung Hsing University)
Abstract：
The Search for Extraterrestrial Intelligence (SETI) has been underway since 1959, gaining even more momentum following the groundbreaking discovery of exoplanets. As we enter a new era in SETI research, there is an unprecedented level of excitement surrounding the field. While traditional SETI research has focused on nearby stellar systems, this presentation aims to shift the spotlight towards the extragalactic universe, what we now refer to as extragalactic SETI.  In our recent work, we have made significant strides by statistically constraining the upper limit of radio transmitters associated with KII-type civilizations in galaxies capable of harnessing energy equivalent to that of a star (~10^26W). Our findings are based on observations conducted by the Breakthrough Listen project. In the talk, I will provide an overview of SETI, explain the motivations behind detecting technological signals in other galaxies, and emphasize the invaluable contributions of the MeerKAT telescope to SETI research.

Title：Cosmological Simulations of Two-Component Wave Dark Matter
Speaker：Hsinhao Huang (NTU)
Abstract：
Wave (fuzzy) dark matter (ψDM) consists of ultralight bosons, featuring a solitonic core within a granular halo. Here we extend ψDM to two components, with distinct particle masses m and coupled only through gravity, and investigate the resulting soliton-halo structure via cosmological simulations. Specifically, we assume ψDM contains 75 per cent major component and 25 per cent minor component, fix the major-component particle mass to m_major=1×10^−22 eV, and explore two different minor-component particle masses with m_major:m_minor=3:1 and 1:3, respectively. For m_major:m_minor=3:1, we find that (i) the major- and minor-component solitons coexist, have comparable masses, and are roughly concentric. (ii) The soliton peak density is significantly lower than the single-component counterpart, leading to a smoother soliton-to-halo transition and rotation curve. (iii) The combined soliton mass of both components follows the same single-component core-halo mass relation. In dramatic contrast, for m_major:m_minor=1:3, a minor-component soliton cannot form with the presence of a stable major-component soliton; the total density profile, for both halo and soliton, is thus dominated by the major component and closely follows the single-component case. To support this finding, we propose a toy model illustrating that it is difficult to form a soliton in a hot environment associated with a deep gravitational potential. The work demonstrates the extra flexibility added to the multi-component ψDM model can resolve observational tensions over the single-component model while retaining its key features.