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The extended inner shadow of Kerr-Taub-NUT black hole with thin disk flows

Yu-Yan Wang, Meng-Die Zhao, Xin-Yu Wang, Guo-Ping Li

Abstract

In this paper, we apply numerical backward ray-tracing to study the observational appearance of Kerr-Taub-NUT (KTN) black holes illuminated by thin accretion disk flows. We obtained the inner shadow, redshift characteristics, and intensity distribution of thin-disk images of the KTN black hole, as observed by a common observer located at different positions. The results show that increasing the spin parameter progressively deforms the critical curve into a "D" shape while simultaneously shrinking and distorting the inner shadow. More importantly, for n = 0.3 at theta_o = 80 degrees, the inner shadow develops a novel "duck-cap-like" morphology with a sharply protruding lower-right edge beyond the critical curve. We term this feature the "extended inner shadow", a structure distinct from the Kerr case. Unlike the standard inner shadow, it consists partly of photons absorbed by the horizon and partly of photons that avoid both absorption and crossing the disk plane, thus receiving no emission. Such deviations from Kerr predictions could be tested by future high-precision astronomical observations, potentially offering new evidence for the existence of NUT charge (or the gravitomagnetic monopole) in black holes.

The extended inner shadow of Kerr-Taub-NUT black hole with thin disk flows

Abstract

In this paper, we apply numerical backward ray-tracing to study the observational appearance of Kerr-Taub-NUT (KTN) black holes illuminated by thin accretion disk flows. We obtained the inner shadow, redshift characteristics, and intensity distribution of thin-disk images of the KTN black hole, as observed by a common observer located at different positions. The results show that increasing the spin parameter progressively deforms the critical curve into a "D" shape while simultaneously shrinking and distorting the inner shadow. More importantly, for n = 0.3 at theta_o = 80 degrees, the inner shadow develops a novel "duck-cap-like" morphology with a sharply protruding lower-right edge beyond the critical curve. We term this feature the "extended inner shadow", a structure distinct from the Kerr case. Unlike the standard inner shadow, it consists partly of photons absorbed by the horizon and partly of photons that avoid both absorption and crossing the disk plane, thus receiving no emission. Such deviations from Kerr predictions could be tested by future high-precision astronomical observations, potentially offering new evidence for the existence of NUT charge (or the gravitomagnetic monopole) in black holes.

Paper Structure

This paper contains 7 sections, 24 equations, 10 figures, 1 table.

Table of Contents

  1. Introduction
  2. Kerr-Taub-NUT black hole and null geodesics
  3. Imaging method and the thin disk model
  4. Imaging method for rotating black hole
  5. Thin disk model around black hole
  6. Images of KTN black hole under the thin disk
  7. Conclusion

Figures (10)

  • Figure 1: Images of KTN black hole with the upper and lower rows correspond to $\theta_o = 80^\circ$ and $\theta_o = 163^\circ$, respectively.
  • Figure 2: The redshift factors of the direct (the first row) and Lensed (the second row)images from the KTN black hole's accretion disk, where red and blue colors represent redshift and blueshift, respectively.
  • Figure 3: The intensity distribution along the x-axis on the screen.
  • Figure 4: The intensity distribution along the y-axis on the screen.
  • Figure 5: The images of a KTN black hole illuminated by a retrograde accretion flow, corresponding to $\theta_o = 80^\circ$.
  • ...and 5 more figures