Russell Boey, along with his coauthors Richard Easther and Yourong Wang, tells us about his simulations of a supermassive black hole traveling through an ultralight dark matter soliton. In particular, he has studied the dynamical friction effect on the black hole within the soliton.

This is especially interesting in the context of the “final parsec” problem, where the orbits of supermassive black hole binary systems stall in their decay as they reach one parsec separation. Maybe a different background, in the form of ULDM instead of WIMP DM, could help?

An ultralight dark matter soliton is much more dense than expectations from “ordinary” WIMP-like dark matter, so it is also expected that the dynamical friction in such a soliton should be large. This is indeed what Russell, Richard and Yourong found (and other coauthor Emily Kendall who isn’t present in the video). However, curiously, they also found a secondary effect where the black hole perturbs the soliton, which in turn causes the soliton to backreact on the black hole and sometimes speed it back up.

There is definitely interesting physics to explore inside galaxies in ultralight dark matter systems, but no verdict just yet on whether the final parsec has been overcome or not.

Russell: profiles.auckland.ac.nz/russell-boey

Richard: profiles.auckland.ac.nz/r-easther

Yourong: fwphys.com

The paper: arXiv 2403.09038

The earlier paper: arXiv 2110.03428