Research Activities of Toshihiro Kawaguchi


Last modified: April, 2025
[1]--[4]: TBD
[5] Conditions for Jet Launching
Conditions of Jet Launching    Black holes over a wide mass range universally eject jets. Although more than a century has passed, its launching mechanisms are still unclear. We then searched for conditions (or precursors) of such jet events.
   We took a close look at the X-ray and radio data obtained for a binary system (a black hole and a star, orbiting around the common barycenter). By calculating the time derivatives and integrals of the data and various quantities, we eventually found the conditions for the jet launching events. Namely, when the inner radius of the gaseous accretion disk surrounding the black hole (i) shrinks fast enough towards the black hole and (ii) reaches to the innermost stable circular orbit, jet ejections happen (Yamaoka, Kawaguchi et al. 2025; Press release).
   (1) Given that dynamic conditions are necessary for a jet launching, any theoretical models/mechanisms that let jets occur in a static condition need modifications. (2) Now that the precursors for jet ejections are unveiled, the success rate of Target-of-Opportunity observations to catch the jet ejections will be raised. (3) In other words, jet ejections are not expected when the inner radius of the accretion disk stays at the innermost stable circular orbit. It means more time to arrange for additional satellites/observatories aiming at observing the next jet ejection. (4) Jets may have played a key role in shaping galaxies over the cosmic history. Our findings above will contribute to figuring out how the universe has evolved.
* Movies [(c) T.Kawaguchi & K.Yamaoka]:
   Low resolution(8Mb), Middle(41Mb), High(132Mb)