Spontaneously Scalarized Kerr Black Holes in Extended Scalar-Tensor-Gauss-Bonnet Gravity

Area of Science:

• Theoretical astrophysics
• General relativity
• Gravitational physics

Background:

• Scalarized black holes (SBHs) are theoretical objects in extended scalar-tensor-Gauss-Bonnet models.
• These models allow for scalar fields that interact with gravity, potentially modifying black hole properties compared to standard general relativity (Kerr black holes).

Purpose of the Study:

• To construct and analyze asymptotically flat, spinning, regular scalarized black holes (SBHs).
• To investigate the domain of existence and properties of these SBHs, particularly their relationship with Kerr black holes and the impact of spin.

Main Methods:

• Construction of spinning, regular SBHs in extended scalar-tensor-Gauss-Bonnet models.
• Scanning the domain of existence for SBHs across different spin values and masses.
• Analysis of thermodynamical favorability (entropy) and dynamical formation mechanisms (tachyonic instability).

Main Results:

• SBHs exist in a mass interval for each spin value, with non-uniqueness compared to Kerr black holes; SBHs are entropically favored.
• SBHs can store significant spacetime energy and exhibit substantial deviations in geodesic frequency and shadow radius compared to Schwarzschild black holes, especially in the static limit.
• Spin selection effects emerge: non-GR effects are pronounced for low-spin SBHs and diminish for spins j≳0.5.

Conclusions:

• SBHs are dynamically favored and can form from Kerr black holes via spontaneous scalarization.
• Spin plays a crucial role in moderating observable deviations from general relativity, with low-spin black holes offering the most significant signatures.
• The study provides a framework for constraining Gauss-Bonnet coupling scales using observational data, such as the M87 black hole shadow.