Soft Matter and Complex Systems Seminar
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2026-06-12 (Friday)
room 1.40, Pasteura 5 at 09:30 
Joanna Piotrowska (California Institute of Technology)What Black Holes Remember: Constraining Their Cosmic Growth with Angular Momentum Measurements
Supermassive black holes are thought to play a central role in shaping the evolution of galaxies, particularly in shutting down star formation in the most massive systems. However, the pathways by which these black holes grow over cosmic time, and how that growth connects to their host galaxies, remain uncertain. A growing body of work combining cosmological simulations and observational surveys indicates that the suppression of star formation is closely linked to black hole activity from the early Universe to the present day. While this connection is now well established, direct constraints on the growth history of supermassive black holes remain limited.
X-ray reflection spectroscopy provides a unique probe of the innermost regions of accretion flows, where strong-gravity effects enable measurements of black hole angular momentum (spin). As a quantity that retains memory of past accretion and merger events, spin offers apowerful observational handle on black hole growth pathways. Recent work has begun to place these measurements in a broader cosmological context by combining spin constraints from X-ray reflection spectroscopy with predictions from galaxy formation models, enabling the first population-level tests of black hole growth scenarios. These efforts move beyond individual objects toward statistical constraints on how supermassive black holes assemble their mass.
The next generation of upcoming X-ray observatories will significantly expand these measurements, enabling a direct link between small-scale accretion physics and the large-scale evolution of galaxies.
X-ray reflection spectroscopy provides a unique probe of the innermost regions of accretion flows, where strong-gravity effects enable measurements of black hole angular momentum (spin). As a quantity that retains memory of past accretion and merger events, spin offers apowerful observational handle on black hole growth pathways. Recent work has begun to place these measurements in a broader cosmological context by combining spin constraints from X-ray reflection spectroscopy with predictions from galaxy formation models, enabling the first population-level tests of black hole growth scenarios. These efforts move beyond individual objects toward statistical constraints on how supermassive black holes assemble their mass.
The next generation of upcoming X-ray observatories will significantly expand these measurements, enabling a direct link between small-scale accretion physics and the large-scale evolution of galaxies.