BHI Colloquium


Tuesday, May 18, 2021, 1:30pm to 2:30pm


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Giacomo Fragione (Astronomy) - Northwestern University (CIERA)

Title: Intermediate-mass black holes: love it or list it 

Abstract: Very little is known about the formation, evolution and demographics of the intermediate-mass black hole (IMBH) family. The classical approach to prove the presence of IMBHs has been to use optical and infrared data to look for the dynamical signatures of IMBHs on stars' orbits. However, this technique is limited to nearby systems due to the small angular size of the IMBH sphere of influence, and has led to claims that later have been revealed to be false alarms. Gravitational wave (GW) and time domain (TD) missions, such as LIGO-Virgo, LISA, JWST, and LSST, promise to shed light on black holes of every size up to the distant Universe. IMBHs lurk in star clusters and galactic nuclei and continuously interact with the surrounding environment. Whenever a merger with a star or a compact object takes place, IMBHs would shine and appear in the frequency band of a TD or GW detector. Moreover, the intermediate mass-ratio inspiral of a stellar compact remnant into an IMBH is a potential target for multi-band detection, since LISA measurements will alert astronomers of an incoming merger detectable within the next few years by LIGO/Virgo/Kagra, Einstein Telescope, and Cosmic Explorer. I will discuss how the host environment structural properties affect the IMBH growth and dynamics, and characterize the typical GW and transient signal expected for current and upcoming missions. GW and TD surveys offer for the first time the opportunity to demonstrate the existence of IMBHs beyond any reasonable doubt and to fill the gap in the BH-mass spectrum. The next decade may bring hundreds of events, promising a spectacular range of new science that touches on nearly every astronomical subfield, from stellar evolution to cosmology.

Bio: Giacomo Fragione is currently a CIERA Fellow and Research Assistant Professor at Northwestern University, since 2019. From 2016 to 2019 he was a Fellow of the Israel Academy of Sciences and Humanities - Arskin Fellow at the Hebrew University of Jerusalem. He obtained his Ph.D. at the Sapienza, University of Rome and University of Tor Vergata in 2016.

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See also: Astronomy