English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We propose a new method for black hole spin measurement. In this method, weconsider a gas blob or ring falling onto a black hole from the marginallystable orbit, keeping its initial orbital angular momentum. We calculate thegas motion and photon trajectories in the Kerr space-time and, assuming thatthe gas blob or ring emits monochromatic radiation, carefully examine how it isobserved by a distant observer. The light curve of the orbiting gas blob iscomposed of many peaks because of periodic enhancement of the flux due to thegravitational lensing and beaming effects. Further, the intensity of each peakfirst gradually increases with time due to the focusing effect around thephoton circular orbit and then rapidly decreases due to the gravitationalredshift, as the gas blob approaches the event horizon. The light curve of thegas ring is equivalent to a superposition of those of the blobs with variousinitial orbital phases, and so it is continuous and with no peaks. The fluxfirst gradually increases and then rapidly decays, as in the blob model. Theflux variation timescale depends on the black hole spin and is independent fromthe inclination angle, while time averaged frequency shift have dependences ofboth effects. We can thus, in principle, determine spin and inclination anglefrom observations. The observational implications and future issues are brieflydiscussed.

New method for black-hole spin measurement based on flux variation from an infalling gas ring