On the instability of Reissner-Nordstrom black holes in de Sitter backgrounds

Recent numerical investigations have uncovered a surprising result: Reissner-Nordstrom-de Sitter black holes are unstable for spacetime dimensions larger than 6. Here we prove the existence of such instability analytically, and we compute the timescale in the near-extremal limit. We find very good agreement with the previous numerical results. Our results may me helpful in shedding some light on the nature of the instability.Comment: Published in Phys.Rev.

From black holes to flux throats: polarization can resolve the singularity

Supersymmetry-breaking is a key ingredient for string theory models to be phenomenologically viable. We review the strong analogy in the physics and the methods used for describing non-supersymmetric flux vacua and non-supersymmetric black holes in string theory. We also show how the polarized state could be the key to describing a well-behaved back-reaction of anti-branes in flux backgrounds, shedding a new light on a recent debate in the literature.Comment: 5 pages, slightly extended contribution to the proceedings of the 21st European String Workshop: "The String Theory Universe" in Leuven, 7-11 Sept 201

Detecting the Birth of Supermassive Black Holes Formed from Heavy Seeds

In this white paper we explore the capabilities required to identify and study supermassive black holes formed from heavy seeds ($\mathrm{M_{\bullet}} \sim 10^4 - 10^6 \, \mathrm{M_{\odot}}$) in the early Universe. To obtain an unequivocal detection of heavy seeds we need to probe mass scales of $\sim 10^{5-6} \, \mathrm{M_{\odot}}$ at redshift $z \gtrsim 10$. From this theoretical perspective, we review the observational requirements and how they compare with planned/proposed instruments, in the infrared, X-ray and gravitational waves realms. In conclusion, detecting heavy black hole seeds at $z \gtrsim 10$ in the next decade will be challenging but, according to current theoretical models, feasible with upcoming/proposed facilities. Their detection will be fundamental to understand the early history of the Universe, as well as its evolution until now. Shedding light on the dawn of black holes will certainly be one of the key tasks that the astronomical community will focus on in the next decade.Comment: White paper submitted to the Astro2020 US decadal surve

On Epistemic Black Holes. How Self-Sealing Belief Systems Develop and Evolve

Many pseudosciences, conspiracy theories and other unfounded belief systems have a self-sealing nature, being equipped with defence mechanisms and immunizing strategies that protect them against counterevidence and criticism. In this paper we discuss the existence of ‘epistemic black holes’, belief systems which posit intelligent agents that are deliberately evading detection and thus sabotaging any investigation into their existence. These belief systems have the remarkable feature that they predict an absence of evidence in their favour, and even the discovery of counterevidence. The most obvious instances of such epistemic black holes are unfounded conspiracy theories, but examples crop up in other domains as well. We outline the development and cultural evolution of epistemic black holes, drawing from a number of case studies. Most importantly, because of their self-sealing character and resilience to counterevidence, epistemic black holes suffer from a recurring problem of arbitrariness and proliferating alternatives. Shedding light on how epistemic black holes function can help to inoculate people against their enduring allure

Formation and Growth of the First Supermassive Black Holes in MOG

The emergence of supermassive black holes (SMBHs) in the early universe remains a topic of profound interest and debate. In this paper, we investigate the formation and growth of the first SMBHs within the framework of Modified Gravity (MOG), where gravity exhibits increased strength. We explore how MOG, as an alternative to the standard model, may offer novel insights into the emergence of SMBHs and potentially reconcile the discrepancies observed in the accretion and growth processes. We examine the dynamics of gas and matter in this modified gravitational framework, shedding light on the unique interplay between gravity and the formation of SMBHs

On Epistemic Black Holes. How Self-Sealing Belief Systems Develop and Evolve

Some belief systems postulate intelligent agents that are deliberately evading detection and thus sabotaging any possible investigation into their existence. These belief systems have the remarkable feature that they predict an absence of evidence in their favor, and even the discovery of counterevidence. Such ‘epistemic black holes’, as we call them, crop up in different guises and in different domains: history, psychology, religion. Because of their radical underdetermination by evidence and their extreme resilience to counterevidence, they develop and evolve in certain predictable ways. Shedding light on how epistemic black holes function can protect us against their allure

Relativistic Collapse of Rotating Supermassive Stars to Supermassive Black Holes

There is compelling evidence that supermassive black holes (SMBHs) exist. Yet the origin of these objects, or their seeds, is still unknown. We are performing general relativistic simulations of gravitational collapse to black holes in different scenarios to help reveal how SMBH seeds might arise in the universe. SMBHs with ~ 10^9 solar masses must have formed by z > 6, or within 10^9 yrs after the Big Bang, to power quasars. It may be difficult for gas accretion to build up such a SMBH by this time unless the initial seed black hole already has a substantial mass. One plausible progenitor of a massive seed black hole is a supermassive star (SMS). We have followed the collapse of a SMS to a SMBH by means of 3D hydrodynamic simulations in post-Newtonian gravity and axisymmetric simulations in full general relativity. The initial SMS of arbitrary mass M in these simulations rotates uniformly at the mass--shedding limit and is marginally unstable to radial collapse. The final black hole mass and spin are determined to be M_h/M ~ 0.9 and J_h/M_h^2 ~ 0.75. The remaining mass goes into a disk of mass M_{disk}/M ~ 0.1. This disk arises even though the total spin of the progenitor star, J/M^2 = 0.97, is safely below the Kerr limit. The collapse generates a mild burst of gravitational radiation. Nonaxisymmetric bars or one-armed spirals may arise during the quasi-stationary evolution of a SMS, during its collapse, or in the ambient disk about the hole, and are potential sources of quasi-periodic waves, detectable by LISA.Comment: 11 pages, to appear in "The Astrophysics of Gravitational Wave Sources", Proceedings of a Workshop held at the University of Maryland in April 2003, ed. J. Centrella, AIP, in pres