Ho-Yun YuChih

I. INTRODUCTION

I work on rotating black holes and what surrounds them. My master's research asked when magnetic reconnection near a Kerr black hole can extract its rotational energy, and found that in a Lorentz-violating bumblebee spacetime this kind of process cannot distinguish the violation from spin. That points me toward gravitational waves: how black-hole environments imprint on them, and whether those imprints can be separated from spin or from departures from general relativity. I am applying for PhD positions starting in 2027.

II. RESEARCH

My master's work is a series on energy extraction from rotating black holes by magnetic reconnection [1]–[4]. Each paper relaxes one assumption the earlier literature fixed for convenience, then measures how much the conclusion depended on it.

A. The plunging bulk plasma and orientation angle

Plasma plunging inside the ISCO favours plasmoids ejected at a positive angle to the flow, which widens the region where the local energy condition holds. [1]

Allowed regions for energy extraction in the ejection-angle versus radius plane at spins 0.9 and 0.998, for plunging and circular plasma — FIG. 1. Allowed regions in the (ξ_B, r₀) plane at a = 0.9 and 0.998. Red: plunging plasma. Blue: circular plasma. Shades run over σ₀ = 1–100.

B. Parameters in reconnection models

Letting the reconnection-model parameters vary shows that the Sweet–Parker limit overestimates how often an accretion flow can extract energy. [2]

Heat maps of the covering factor over black-hole spin and geometric index — FIG. 2. Covering factor χ over spin a and geometric index g, for σ₀ = 4 (top) and 50 (bottom); plunging (left) and circular (right) plasma.

C. Bumblebee gravity

In a rotating Einstein–bumblebee spacetime, the Lorentz-violating parameter enters every stationary equatorial quantity only through the effective spin ã = a√(1+l). [3]

Covering factor over the Lorentz-violation and charge parameters, with curves along fixed lines and along a contour of irreducible mass — FIG. 3. Covering factor over the (l, b) plane at a = 0.998. Along a contour of fixed irreducible mass it peaks where the horizon is about to vanish, at (l, b) ≈ (−0.52, 0.62).

D. Destinies of plasmoids from reconnection in the ergoregion

Requiring the energetic plasmoid to actually escape sets a spin floor of a ≈ 0.80: below it, reconnection cannot extract energy at any magnetization. [4]

Grid of maps showing whether the ejected plasmoid escapes, stays bound, or falls into the hole, for three spins and three magnetizations — FIG. 4. Fate of the energetic plasmoid in the (ξ_B, r₀) plane for a = 0.8, 0.9, 0.998 and σ₀ = 2, 10, 100: escape, bound, or captured. Outlined: where its partner carries negative energy.

ACKNOWLEDGMENTS

The author co-founded, and serves as Vice Chairman of, the Taiwan Youth Science Development Association, and writes popular-science articles in Chinese on black holes, symmetry, superradiance and dark matter. A talk at the Taiwan Youth Science Development Forum is scheduled for December 2026.

Y. Shen,* H.-Y. YuChih,* and B. Chen, Energy extraction from a rotating black hole via magnetic reconnection: The plunging bulk plasma and orientation angle, Phys. Rev. D 110, 123010 (2024).
Y. Shen* and H.-Y. YuChih,* Energy extraction from a rotating black hole via magnetic reconnection: Parameters in reconnection models, Phys. Rev. D 111, 023003 (2025).
H.-Y. YuChih and Y. Shen, Energy extraction from a rotating black hole via magnetic reconnection: Bumblebee gravity, Phys. Rev. D (2025).
H.-Y. YuChih and Y. Shen, Destinies of plasmoids formed from the magnetic reconnection occurring within the ergo region of a rotating black hole, accepted (2026).

*These authors contributed equally.

Ho-Yun YuChih received the B.S. degree in materials science (physics track) from Duke Kunshan University in 2022 and the M.S. degree in theoretical physics from Peking University in 2026.