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BHI Colloquium

Monday, February 26, 2024
11:00 AM – 12:00 PM

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Send Me News from BHI

BHI Colloquium

Sibasish Laha


Title: Activities at the centers of Active Galactic Nuclei

Abstract: Active galactic nuclei (AGNs) are the power houses at the center of galaxies hosting an actively accreting supermassive black hole (SMBH). The accretion disk radiates a large amount of accretion power and produces outflows in the form of winds and/or relativistic jets, and also sustains an X-ray emitting corona.  Much has been theorized and observed in this topic in the last several decades, but a few fundamental questions still elude us: For example, What is the exact geometry of the central engine?  How does matter at larger distances (>1 pc) lose angular momentum, fall and feed the accretion disk?  How powerful outflows are generated from the heart of these massive black holes? How is the AGN corona formed and energetically sustained near the SMBH? In this talk I will highlight some of the recent observational advancements towards understanding these questions. Extensive  studies on highly energetic outflows have shed some light on the global properties of this phenomenon which apparently connects the SMBH with the host galaxy (cosmic coevolution).  Similarly, short and long term X-ray obscuration variability has given us hints about the nature of the cold/neutral matter (torus) possibly feeding the SMBH. The most recent time-domain phenomenon of changing look AGN has opened up the flood-gates for our understanding of the accretion process itself, and the behavior and nature of the AGN X-ray coronal emission.

Bio: Dr. Sibasish  Laha has completed his Ph.D. in astrophysics from the Inter-University Center for Astronomy and Astrophysics in India in 2014. Following which he was a post-doc at Queen’s University of Belfast, UK and then a post-doc at University of California San Diego, USA. Sibasish joined NASA Goddard Space Flight Center in 2019 to serve as one of the lead team members of the Swift satellite mission, supporting the BAT telescope. He is currently the Swift-BAT mission support scientist and Swift Science community outreach Lead. He has extensively worked on AGN X-ray astrophysics and have written an invited review on AGN outflows in Nature Astronomy, published in 2021. Sibasish’s work on an intriguing changing look AGN 1ES 1927+654 showed a possible magnetic pole inversion as the cause for vanishing Coronal emission, which resulted in a NASA press release in 2022. He was subsequently awarded: NASA Goddard Exceptional achievement for Science in 2022, and then NASA Exceptional Scientific achievement Medal 2022 for his achievements. He continues to be a passionate researcher on the interesting phenomenon of AGN.


Monday, February 26, 2024 11:00 AM - 12:00 PM


BHI Publication

Expanding Sgr A* dynamical imaging capabilities with an African extension to the Event Horizon Telescope

April 1, 2023
Kantzas, D.; Markoff, S.; Lucchini, M.; Ceccobello, C.; Chatterjee, K.
Astrophysical jets are relativistic outflows that remain collimated for remarkably many orders of magnitude. Despite decades of research, the…
Read The BHI Publication