Influence of torsion charge on shadow and observation signature of black hole surrounded by various profiles of accretions

In this paper, we carefully study the shadow and observational signature of the black hole with torsion charge for a distant observer, and further compare the results with that gotten in Schwarzschild spacetime. For thin disk accretion cases, the result shows that there are not only dark areas in the observed image of black hole, but also photon rings and lensing rings, which are closely associated with the torsion charge. The change of torsion charge will directly affect the range of photon ring and lens ring, and the contribution proportion of these rings to the observed intensity. In addition, the total flux of observed intensity is mainly provided by direct emission, and the lensing ring and photon ring contribute only a small part. By further considering the static and infalling cases of spherically symmetric accretion, one can find that the observed image is much darker for the falling accretion matters, but the shadow radius does not change. However, both the observed intensity and shadow size are significantly different when the torsion charge changes. That is, the size of the observed shadow is related to the spacetime geometry. In addition, based on the shadow of M87, we also constraint the torsion charge of black hole by using the diameter of shadow approximately. Finally, by comparing our results and that in Schwarzschild spacetime, it shows that black hole shadow can provide a feasible method for distinguishing those two spacetime.

Automated summary

In this paper, the authors study the shadow and observational signature of a black hole with torsion charge and compare the results with those obtained in Schwarzschild spacetime. The study shows that for thin disk accretion cases, the observed image of the black hole exhibits dark areas, photon rings, and lensing rings, which are closely related to the torsion charge. The change of torsion charge affects the range of photon and lens rings as well as their contribution to the observed intensity. Additionally, the observed intensity is mainly provided by direct emission, while the lensing and photon rings contribute only a small part. The authors also find that the observed image is darker for falling accretion matters, but the shadow radius remains unchanged. However, both the observed intensity and shadow size significantly differ when the torsion charge changes. Based on the shadow of M87, the authors also constrain the torsion charge of the black hole. Comparing the results with those in Schwarzschild spacetime, it is evident that the black hole shadow can serve as a feasible method for distinguishing different spacetimes.