The study of black holes has captivated the scientific community for decades, fueling countless research endeavors to unravel their enigmatic nature. Recently, researchers at the University of California–Santa Barbara, University of Warsaw, and University of Cambridge conducted a theoretical study specifically focusing on extremal Kerr black holes. Their research, published in Physical Review Letters, reveals that these unique black holes could serve as potent amplifiers of new and unknown physics. Let’s delve deeper into this intriguing study, exploring the potential implications and significance of their findings.
Initially, the researchers’ investigation originated from a previous project, where they examined cold extremal black holes in the presence of a cosmological constant. Surprisingly, their research showed that these black holes, under infinite tidal forces, would crush any living beings before reaching the center. However, when the cosmological constant is assumed to be zero, as often observed in astrophysical scenarios, this effect vanishes. These findings challenged previous beliefs and prompted the researchers to explore further.
During a discussion at UC Santa Barbara’s Gravity Lunch seminar, Grant Remmen shared an intriguing idea with Gary Horowitz, involving higher-derivative terms in a gravitational effective field theory (EFT). They hypothesized that these terms, quantum corrections to the Einstein equations, might lead to singularities on the horizons of extremal black holes. Curious about the potential implications, they initiated a collaboration with Maciej Kolanowski and Jorge Santos to test this idea through a series of calculations.
Extremal black holes possess the highest possible rotation rate, causing their horizons to approach the speed of light. The researchers’ calculations unveiled that the higher-derivative EFT corrections transform the horizons of extremal black holes into singularities with infinite tidal forces. In normal black holes, tidal forces only become infinite at the center. However, in extremal black holes, the EFT corrections cause the singularity to extend all the way to the horizon, defying conventional expectations. Moreover, the researchers observed that the strength of the tidal divergence and the occurrence of tidal singularities were heavily influenced by the EFT coefficients.
The implications of these findings suggest that the spacetime geometry near the horizon of extremal black holes is sensitive to new physics at higher energies. Remarkably, the unexpected singularity manifests itself even with the EFT coefficients from the Standard Model of particle physics. This surprising result challenges the notion of decoupling between different distance scales and implies that the low-energy description of physics can break down at the horizon of rapidly spinning black holes.
The calculations conducted by this team of researchers shed light on the potential of extremal Kerr black holes as tools for probing new physical phenomena. While it was not anticipated that the horizon of these black holes would possess infinite tidal forces in the EFT, their results clearly demonstrate otherwise. Moving forward, the researchers aim to investigate whether these singularities can be resolved by exploring ultraviolet physics. They ponder whether the horizon’s sensitivity to new physics persists all the way to the Planck scale or if it smooths out at the short-distance scale associated with the EFT.
The groundbreaking research on extremal Kerr black holes highlights their capacity to amplify and uncover new physics. By exploring the effects of quantum corrections and higher-derivative terms, the researchers uncovered unexpected singularities on the horizons of extremal black holes, challenging previous understanding. These findings demonstrate the crucial role that extremal Kerr black holes could play in expanding our knowledge of the universe and the fundamental laws of physics. The future holds exciting possibilities as scientists continue to delve into the mysteries of these cosmic marvels.