Gravitational waves have been detected from the mergers of nearly ni nety binary black holes during the first three observing runs of the Advan ced LIGO and Virgo detectors. In this talk\, I will discuss these detectio ns and their implications for understanding fundamental properties of matt er and spacetime \;in two contexts. First\, I will review a nonlinear effect in general relativity called the gravitational-wave memory. The eff ect is characterized by a lasting change in the gravitational-wave strain produced by the energy radiated in gravitational waves. I will describe ho w this effect is related to the infrared properties of gravity\, how the m emory effect can be measured with LIGO and Virgo\, and how new types of me mory effects have been recently predicted. Second\, I will discuss how den se distributions of dark matter around a black hole can influence the insp iral of a second compact object and thus the gravitational waves emitted f rom such a binary. With the planned space-based gravitational-wave detecto r LISA\, the distribution of dark matter on these small scales could be ma pped precisely. This would provide a new method to study dark matter: with gravitational waves.

\n DTSTART:20220121T203000Z LOCATION:Physics Building\, Room 204 SUMMARY:Studying matter and spacetime with gravitational waves END:VEVENT END:VCALENDAR