Delve into the fascinating world of ultralight boson clouds surrounding black holes in this second lecture by Nils Siemonsen from Princeton University. Explore advanced concepts in gravitational-wave astronomy as part of the Summer School on Gravitational-Wave Astronomy organized by the International Centre for Theoretical Sciences. Learn about exotic sources of gravitational waves and their potential detection in upcoming observing runs of LIGO, Virgo, and KAGRA. Gain insights into the cutting-edge research on continuous gravitational waves from sources like rapidly spinning neutron stars and axion clouds around black holes. Expand your understanding of astrophysics, gravitational wave detection methods, and the latest developments in this exciting field of study.