The Unusual Active Galaxy H1821+643 and the Elusive Nature of FRI Quasars

David Garofalo, Chandra B. Singh

Research output: Contribution to journalArticlepeer-review


The moderate spin estimate for the black hole at the center of the cool core cluster H1821+643 motivates the completion of a story about this object’s origin and evolution that was in the making since the work by Blundell & Rawlings over two decades ago as the first example of a massive black hole accreting at near-Eddington rates with an FRI jet. This elusive combination of properties was explained in our 2010 model where we showed it to be part of a small parameter space that includes X-shaped radio galaxies. As an accreting black hole that never experienced a counterrotating phase, H1821+643 is constrained by theory to produce a jet for spin values a satisfying 0.1 < a < ∼ 0.7 and an FRI jet for a slightly smaller range. The feedback from such a black hole is not subject to a tilted jet and is why star formation rates remain high in this cluster environment. The prediction is that H1821+643 is within millions of years of becoming jetless.

Original languageEnglish
Article number094102
JournalPublications of the Astronomical Society of the Pacific
Issue number1039
StatePublished - 1 Sep 2022
Externally publishedYes


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