Speaker: Lorenzo Sironi, Columbia University
Life on the edge: reconnection-powered emission at the boundaries of black hole jets
Abstract: The boundaries of relativistic black hole jets—at the interface between the jet and the disk wind—lie at the core of our recent understanding of jet-powered phenomena. They harbor intense velocity and magnetic shears, which provide the free energy needed to power a number of observational signatures. We demonstrate that magnetic reconnection—a process by which opposite field lines annihilate, releasing their energy to the plasma—ultimately governs dissipation of the available free energy at jet boundaries. Reconnection resulting from the nonlinear evolution of Kelvin-Helmholtz type vortices can naturally explain the limb-brightened radio emission of AGN jets, such as M87. Also, inverse Compton scattering within the chain of magnetic islands / flux ropes self-consistently created by reconnection at the jet boundaries can power the mysterious hard X-ray “coronal” emission of X-ray binaries. We will also argue that reconnection-driven hadronic acceleration in the coronal regions of NGC 1068 may be the source of the TeV neutrinos recently detected by IceCube.
Bio: Lorenzo Sironi is an associate professor in the Department of Astronomy at Columbia. His research group investigates how fundamental plasma processes, shocks, magnetic reconnection and turbulence can power the non-thermal signatures of a wide variety of astrophysical objects, especially the most powerful and compact sources in our universe: neutron stars and black holes. Most recently, Sironi has become fascinated with the rich and puzzling phenomenology of fast radio bursts and with the hard X-ray “coronal” emission of X-ray binaries and active galactic nuclei. He has a decade-long interest in magnetic dissipation and particle acceleration in relativistic black hole jets, focusing both on their multi-wavelength emission as well as on their potential role as multi-messenger sources (ultra-high-energy cosmic rays and high-energy neutrinos).
By modeling the plasma physics of high-energy astrophysical sources from first principles, Sironi and his group aim to build self-consistent, falsifiable models of their observables. By creating a diverse and inclusive environment that benefits everyone’s scientific efforts, he strives to foster the growth of the next cohort of plasma astrophysicists.
Sironi became passionate about astronomy and plasmas at the University of Pisa before moving to the Department of Astrophysical Sciences at Princeton University for his Ph.D. After working as a NASA Einstein Fellow at Harvard University, he moved to Columbia in 2016. He has been awarded the 2019 Sloan Fellowship in Physics, the 2020 Cottrell Scholar Award and the 2023 Department of Energy Early Career Award.
Event details: In-person seminars are only available to CU ID holders. At this time, Non-Columbia affiliates and the general public are only invited to participate remotely. Contact [email protected] if you would like the Zoom link for this seminar.