The most important task of gravitational-wave astronomy in the next 5-10 years is to simply detect more sources. It is analogous to the development in the field of exoplanets. During the 1990s, when only a couple of hot Jupiters were detected, the scientific questions were focusing on the formation of such system. Now, thousands of exoplanets have been confirmed, in all kinds of sizes and configurations, which have immensely diversified our concept of a planetary system and profoundly revolutionized our view of planet formation and evolution.

We are expecting a similar paradigm shift as the number of gravitational-wave sources increases. This prediction is based on the ongoing efforts of (i) upgrading the Advanced LIGO/Virgo detectors with boosted sensitivity, (ii) constructing a network of ground-based gravitational-wave observatories including the new nodes in Japan and India, (iii) forming an international consortium of Pulsar Timing Array (PTA) to improve the timing accuracy of pulsars, and (iv) in about 20 years launching a gravitational-wave observatory into space, as promised by the mission of the Laser Interferometer Space Antenna (LISA).

Foreseeable breakthroughs include (a) accumulating a critical number of binary neutron stars or binary stellar black holes to reveal their formation and evolution history as a population, (b) pinpointing the sky location of LIGO/Virgo sources with an accuracy of 1 square degree to allow unique identification of the electromagnetic counterparts and do real “multi-messenger” astronomy, (c) detecting gravitational waves from merging monsters, supermassive black holes in the local universe, (d) detecting intermediate or the so-called “seed” black holes at high redshift, even earlier than the time of reionization, and last but not least, some completely unexpected discoveries.

The faculty members of KIAA and the Department of Astronomy at PKU are actively conducting research in the above fields. The topics include testing gravity theories using gravitational waves, inferring the underlying astrophysical processes, and developing hardwares and softwares that can be implemented to detect gravitational waves. These activities have been recognized internationally and will continue to enrich the science cases for future gravitational-wave observations. Moreover, the faculty members have established a variety of collaborations with the international community of gravitational-wave researches, including the International PTA, the LISA consortium, and the LIGO/Virgo Science Collaboration, as well as with the gravitational-wave related programs in China.

These effects have resulted in the gathering of a core group of people with the same interest in gravitational waves at PKU (Pau Amaro-Seoane, Xian Chen, Kohei Inayoshi, Yanfei Jiang, Kejia Lee, Lixin Li, Zhuo Li, Fukun Liu, Lijing Shao, Rainer Spurzem, Renxin Xu, Qingjuan Yu, Bing Zhang). This group is starting to conduct cutting-edge research in gravitational-wave related theories and technologies, to generate new science cases and concepts for future gravitational-wave programs, and to foster the exchange of ideas and expertise between China the international gravitational-wave community.