Black Hole Remnants Research Articles

Extending black-hole remnant surrogate models to extreme mass ratios

Extending black-hole remnant surrogate models to extreme mass ratios

Remnant black hole properties from numerical-relativity-informed perturbation theory and implications for waveform modeling

Remnant black hole properties from numerical-relativity-informed perturbation theory and implications for waveform modeling

A Black Hole Kicked at Birth: MAXI J1305-704

When a compact object is formed in a binary, any mass lost during core collapse will impart a kick on the binary’s center of mass. Asymmetries in this mass loss or neutrino emission would impart an additional natal kick on the remnant black hole or neutron star, whether it was formed in a binary or in isolation. While it is well established that neutron stars receive natal kicks upon formation, it is unclear whether black holes do as well. Here, we consider the low-mass X-ray binary MAXI J1305-704, which has been reported to have a space velocity ≳200 km s−1. In addition to integrating its trajectory to infer its velocity upon formation of its black hole, we account for recent estimates of its period, black hole mass, mass ratio, and donor effective temperature from photometric and spectroscopic observations. We find that if MAXI J1305-704 formed via isolated binary evolution in the thick Galactic disk, then the supernova that formed its black hole imparted a natal kick of at least 70 km s−1 while ejecting less than ≃1 M ⊙ with 95% confidence assuming uninformative priors on mass loss and natal kick velocity.

Gravitational wave hints black hole remnants as dark matter

The end state of Hawking evaporation of a black hole is uncertain. Some candidate quantum gravity theories, such as loop quantum gravity and asymptotic safe gravity, hint towards Planck sized remnants. If so, the Universe might be filled with remnants of tiny primordial black holes, which formed with mass g. A unique scenario is the case of g, where tiny primordial black holes reheat the Universe by Hawking evaporation and their remnants dominate the dark matter (DM). Here, we point out that this scenario leads to a cosmological gravitational wave signal at frequencies ∼100 Hz. Finding such a particular gravitational wave signature with, e.g. the Einstein telescope, would suggest black hole remnants as DM.

Black Hole Solutions with Dark Matter Halos in the Four‐Dimensional Einstein‐Gauss‐Bonnet Gravity

AbstractBlack holes (BHs) convey information about different matter‐energy distributions in their immediate environment, as they bear the imprints of the intrinsic spacetime geometry and exotic surrounding matter. In this regard, exact spherically symmetric regular black hole (BH) solutions supported by two phenomenological distributions of dark matter galactic halos in Eintein‐Gauss‐Bonnet gravity are explored. Analytical solutions for the metric and the corresponding thermodynamic properties, including heat capacity (), Gibbs' free energy (), and Hawking temperature () associated with the BH's horizon radius and quasinormal modes (QNMs) are found. The specific heat is investigated, and it is discovered that a Hawking‐Page phase transition with divergent occurred at a critical radius, . Consequently, the authors have regular BHs with Cauchy and event horizons, and evaporation results in thermodynamically stable double‐horizon BH remnants with zero temperatures. The QNMs of the scalar field perturbations on the regular background of the BHs are then discussed comprehensively.

Thermodynamics and Shadows of quantum-corrected Reissner–Nordström black hole surrounded by quintessence

In this work, we consider the quantum-corrected Reissner–Nordström black hole surrounded by quintessence matter and examine its thermodynamics and shadow. To this end, we handle the quantum-corrected metric of the black hole, which is given by Wu and Lui in 2022, and couple the quintessence matter field effects to the lapse function. Then, we obtain the mass, Hawking temperature, specific heat, and equation of state functions. In all these functions, we discuss two cases in which the quantum corrections are greater or smaller than the quintessence matter effects. We observe that within these two scenarios, the black hole has different characteristic thermal behaviors. Moreover, we find that the quintessence matter plays an important role in leading to a black hole remnant. Furthermore, we observe that black hole behaves like Van der Waals fluid. Finally, we investigate the black hole shadow by Carter’s approach. We find that quintessence matter and quantum corrections modify the shadow of the black hole.

Thermodynamic properties of Schwarzschild black hole in non-commutative gauge theory of gravity

In this paper, we use the non-commutative (NC) gauge theory of gravity to investigate the thermodynamic properties of a deformed Schwarzschild Black Hole (SBH). Our results present a new scenario of black hole evaporation. As a first step, we describe the Arnowitt–Deser–Misner (ADM) mass, the Hawking temperature, and the entropy of NC SBH. The non-commutativity removes the divergent behavior of temperature, and the result shows a difference in the pole-equator temperature. These corrections also reveal a new fundamental length at the Planck scale order, Θ∼10−35m. In the last stage of evaporation, the NC correction exposes a remnant entropy S0Θ of the NC SBH with a minimal mass mˆ0, where the non-commutativity prevents the black hole from evaporating more than this minimal mass. Then, the description of the heat capacity and the Helmholtz free energy of the deformed black hole shows the effect of the NC gauge theory on the thermodynamic stability and the phase transitions. Finally, we investigate the influence of the black hole pressure on the stability and the phase transition of SBH in NC space–time. In the final stage of this scenario, the remnant black hole is thermodynamically stable. In this study, we find that the NC parameter plays a role similar to the thermodynamic variable. The results show a second-order phase transition of NC SBH.

Binary boson stars: Merger dynamics and formation of rotating remnant stars

Scalar boson stars have attracted attention as simple models for exploring the nonlinear dynamics of a large class of ultra compact and black hole mimicking objects. Here, we study the impact of interactions in the scalar matter making up these stars. In particular, we show the pivotal role the scalar phase and vortex structure play during the late inspiral, merger, and post-merger oscillations of a binary boson star, as well as their impact on the properties of the merger remnant. To that end, we construct constraint satisfying binary boson star initial data and numerically evolve the nonlinear set of Einstein-Klein-Gordon equations. We demonstrate that the scalar interactions can significantly affect the inspiral gravitational wave amplitude and phase, and the length of a potential hypermassive phase shortly after merger. If a black hole is formed after merger, we find its spin angular momentum to be consistent with similar binary black hole and binary neutron star merger remnants. Furthermore, we formulate a mapping that approximately predicts the remnant properties of any given binary boson star merger. Guided by this mapping, we use numerical evolutions to explicitly demonstrate, for the first time, that rotating boson stars can form as remnants from the merger of two non-spinning boson stars. We characterize this new formation mechanism and discuss its robustness. Finally, we comment on the implications for rotating Proca stars.

Measuring the ringdown scalar polarization of gravitational waves in Einstein-scalar-Gauss-Bonnet gravity

We model the scalar waves produced during the ringdown stage of binary black hole coalescence in Einstein scalar Gauss-Bonnet (EsGB) gravity, using numerical relativity simulations of the theory in the decoupling limit. Through a conformal coupling of the scalar field to the metric in the matter-field action, we show that the gravitational waves in this theory can have a scalar polarization. We model the scalar quasi-normal modes of the ringdown signal in EsGB gravity, and quantify the extent to which current and future gravitational wave detectors could observe the spectrum of scalar radiation emitted during the ringdown phase of binary black hole coalescence. We find that within the limits of the theory's coupling parameters set by current theoretical and observational constraints, the scalar ringdown signal from black hole remnants in the $10^1 - 10^3 \, M_{\odot}$ mass range is expected to be well below the detectability threshold with the current network of gravitational-wave detectors (LIGO-Virgo-KAGRA), but is potentially measurable with next-generation detectors such as the Einstein Telescope.

Hierarchical triple mergers: testing Hawking’s area theorem with the inspiral signals

ABSTRACT Hawking’s area theorem is one of the fundamental laws of black holes (BHs), which has been tested at a confidence level of $\sim 95~{{\ \rm per\ cent}}$ with gravitational wave (GW) observations by analysing the inspiral and ringdown portions of GW signals, independently. In this work, we propose to carry out the test in a new way with the hierarchical triple merger (i.e. two successive BH mergers occurred sequentially within the observation window of GW detectors), for which the properties of the progenitor BHs and the remnant BH of the first coalescence can be inferred from the inspiral portions of the two mergers. As revealed in our simulations, the BH area law can be well confirmed for some plausible hierarchical triple merger events detectable in LIGO/Virgo/KAGRA/LIGO-India’s O4/O5 runs. Our proposed method provides significant facilitation for testing the area law and complements previous methods.

The dominating mode of two competing massive modes of quadratic gravity

Over the last two decades, motivations for modified gravity have emerged from both theoretical and observational levels. f(R) and Chern-Simons gravity have received more attention as they are the simplest generalization. However, f(R) and Chern-Simons gravity contain only an additional scalar (spin-0) degree of freedom and, as a result, do not include other modes of modified theories of gravity. In contrast, quadratic gravity (also referred to as Stelle gravity) is the most general second-order modification to 4-D general relativity and contains a massive spin-2 mode that is not present in f(R) and Chern-Simons gravity. Using two different physical settings—the gravitational wave energy-flux measured by the detectors and the backreaction of the emitted gravitational radiation on the spacetime of the remnant black hole—we demonstrate that massive spin-2 mode carries more energy than the spin-0 mode. Our analysis shows that the effects are pronounced for intermediate-mass black holes, which are prime targets for LISA.

Black hole mergers as tracers of spinning massive black hole and galaxy populations in the OBELISK simulation

Massive black hole (BH) mergers will be key targets of future gravitational wave and electromagnetic observational facilities. In order to constrain BH evolution with the information extracted from BH mergers, one must take into account the complex relationship between the population of merging BHs and the global BH population. We analysed the high-resolution cosmological radiation-hydrodynamics simulation OBELISK, run to redshift z = 3.5, to study the properties of the merging BH population, and its differences with the underlying global BH population in terms of BH and galaxy properties. In post-processing, we calculated dynamical delays between the merger in the simulation at the resolution limit and the actual coalescence well below the resolution scale. We find that merging BHs are hosted in relatively massive galaxies with stellar mass M* ≳ 109 M⊙. Given that galaxy mass is correlated with other BH and galaxy properties, BH mergers tend to also have a higher total BH mass and higher BH accretion rates than the global population of main BHs. These differences generally disappear if the merger population is compared with a BH population sampled with the same galaxy mass distribution as merger hosts. Galaxy mergers can temporarily boost the BH accretion rate and the host’s star formation rate, which can remain active at the BH merger if sub-resolution delays are not taken into account. When dynamical delays are taken into account, the burst has generally faded by the time the BHs merge. BH spins are followed self-consistently in the simulation under the effect of accretion and BH mergers. We find that merging BHs have higher spins than the global population, but similar or somewhat lower spins compared to a mass-matched sample. For our sample, mergers tend to decrease the spin of the final BH remnant.

Black Hole Spectroscopy by Mode Cleaning.

We formulate a Bayesian framework to analyze ringdown gravitational waves from colliding binary black holes and test the no-hair theorem. The idea hinges on mode cleaning-revealing subdominant oscillation modes by removing dominant ones using newly proposed "rational filters." By incorporating the filter into Bayesian inference, we construct a likelihood function that depends only on the mass and spin of the remnant black hole (no dependence on mode amplitudes and phases) and implement an efficient pipeline to constrain the remnant mass and spin without Markov chain MonteCarlo. We test ringdown models by cleaning combinations of different modes and evaluating the consistency between the residual data and pure noise. The model evidence and Bayes factor are used to demonstrate the presence of a particular mode and to infer the mode starting time. In addition, we design a hybrid approach to estimate the remnant black hole properties exclusively from a single mode using Markov chain MonteCarlo after mode cleaning. We apply the framework to GW150914 and demonstrate more definitive evidence of the first overtone by cleaning the fundamental mode. This new framework provides a powerful tool for black hole spectroscopy in future gravitational-wave events.

Using rational filters to uncover the first ringdown overtone in GW150914

There have been debates in the literature about the existence of the first overtone in the ringdown of GW150914. We develop a novel Bayesian framework to reanalyze the data of this event, by incorporating a new technique, the ``rational filter'' that can clean particular modes from the ringdown signal. We examine the existence of the first overtone in GW150914 from multiple novel perspectives. First, we confirm that the estimates of the remnant black hole mass and spin are more consistent with those obtained from the full inspiral-merger-ringdown signal when including the first overtone at an early stage of the ringdown (right after the inferred signal peak); such improvement fades away at later times. Second, we formulate a new way to compare the ringdown models with and without the first overtone by calculating the Bayes factor at different times during the ringdown. We obtain a Bayes factor of 600 at the time when the signal amplitude reaches its peak. The Bayes factor decreases sharply when moving away from the peak time and eventually oscillates around a small value when the overtone signal is expected to have decayed. Third, we clean the fundamental mode from the ringdown of GW150914 and estimate the amplitudes of the modes using the filtered data with Markov chain Monte Carlo (MCMC). The inferred amplitude of the fundamental mode is $\ensuremath{\sim}0$ whereas the amplitude of the first overtone remains almost unchanged, implying that the filtered data is consistent with a first-overtone-only template. Similarly, if we remove the first overtone from the GW150914 data, the filtered data are consistent with a fundamental-mode-only template. Finally, after removing the fundamental mode, we use MCMC to infer the remnant black hole mass and spin from the first overtone alone. We find the posteriors are still informative and consistent with those inferred from the fundamental mode. The conclusions are also verified through simulations in Gaussian noise using a GW150914-like numerical relativity waveform.

Diffuse emission from black hole remnants

At the end of its evaporation, a black hole may leave a remnant where a large amount of information is stored. We argue that the existence of an area gap as predicted by loop quantum gravity removes a main objection to this scenario. Remnants should radiate in the low-frequency spectrum. We model this emission and derive properties of the diffuse radiation emitted by a population of such objects. We show that the frequency and energy density of this radiation, which are measurable in principle, suffice to estimate the mass of the parent holes and the remnant density, if the age of the population is known.

Gravitational Wave Signal for Quark Matter with Realistic Phase Transition.

The cores of neutron stars (NSs) near the maximum mass can realize a transitional change to quark matter (QM). Gravitational waves from binary NS mergers are expected to convey information about the equation of state (EOS) sensitive to the QM transition. Here, we present the first results of gravitational wave simulation with the realistic EOS that is consistent with abinitio approaches of χEFT and pQCD and is assumed to go through smooth crossover. We compare them to results obtained with another EOS with a first-order hadron-quark phase transition. Our results suggest that early collapse to a black hole in the post-merger stage after NS merger robustly signifies softening of the EOS associated with the QM onset in the crossover scenario. The nature of the hadron-quark phase transition can be further constrained by the condition that electromagnetic counterparts should be energized by the material left outside the remnant black hole.

Gravitational recoil from binary black hole mergers in scalar field clouds

In vacuum, the gravitational recoil of the final black hole from the merger of two black holes depends exclusively on the mass ratio and spins of the coalescing black holes, and on the eccentricity of the binary. If matter is present, accretion by the merging black holes may modify significantly their masses and spins, altering both the dynamics of the binary and the gravitational recoil of the remnant black hole. This paper considers such a scenario. We investigate the effects on the kick of the final black hole from immersing the binary in a scalar field cloud. We consider two types of configurations: one with nonspinning and unequal-mass black holes, and a second with equal mass and spinning holes. For both types, we investigate how the gravitational recoil of the final black hole changes as we vary the energy density of the scalar field. We find that the accretion of the scalar field by the merging black holes could have a profound effect. For the nonspinning, unequal-mass binary black holes, the kicks are in general larger than in the vacuum case, with speeds of $\ensuremath{\sim}1,200\text{ }\text{ }\mathrm{km}/\mathrm{s}$ for binaries with mass ratio $2\ensuremath{\mathbin:}1$, 1 order of magnitude larger than in vacuum. For equal mass, binaries with black holes with spins aligned with the orbital angular momentum, kicks larger than in vacuum are also found. For systems with spins in the superkick configuration, the scalar field triggers a similar dependence of the kicks with the entrance angle at merger as in the vacuum case but in this case depending on the strength of the scalar field.

Black-hole ringdown as a probe of higher-curvature gravity theories

Detecting gravitational waves from coalescing compact binaries allows us to explore the dynamical, nonlinear regime of general relativity and constrain modifications to it. Some of the gravitational-wave events observed by the LIGO-Virgo Collaboration have sufficiently high signal-to-noise ratio in the merger, allowing us to probe the relaxation of the remnant black hole to its final, stationary state---the so-called black-hole ringdown, which is characterized by a set of quasinormal modes. Can we use the ringdown to constrain deviations from general relativity, as predicted by several of its contenders? Here, we address this question by using an inspiral-merger-ringdown waveform model in the effective-one-body formalism, augmented with a parametrization of the ringdown based on an expansion in the final black hole's spin. We give a prescription on how to include in this waveform model, the quasinormal mode frequencies calculated on a theory-by-theory basis. In particular, we focus on theories that modify general relativity by higher-order curvature corrections, namely, Einstein-dilaton-Gauss-Bonnet, dynamical Chern-Simons theories, and cubic- and quartic-order effective-field-theories of general relativity. We use this parametrized waveform model to measure the ringdown properties of the two loudest ringdown signals observed so far, GW150914 and GW200129. We find that while the Einstein-dilaton-Gauss-Bonnet theory cannot be constrained with these events, we can place upper bounds on the fundamental lengthscale of cubic- (${\ensuremath{\ell}}_{\text{cEFT}}\ensuremath{\le}38.2\text{ }\text{ }\mathrm{km}$) and quartic-order (${\ensuremath{\ell}}_{\text{qEFT}}\ensuremath{\le}51.3\text{ }\text{ }\mathrm{km}$) effective-field-theories of general relativity, and of dynamical Chern-Simons gravity (${\ensuremath{\ell}}_{\text{dCS}}\ensuremath{\le}38.7\text{ }\text{ }\mathrm{km}$). The latter result is a concrete example of a theory presently unconstrained by inspiral-only analyses which, however, can be constrained by merger-ringdown studies with current gravitational-wave data.

Black hole remnants are not too fast to be dark matter

We comment on recent claims that recoil in the final stages of Hawking evaporation gives black hole remnants large velocities, rendering them inviable as a dark matter candidate. We point out that due to cosmic expansion, such large velocities at the final stages of evaporation are not in tension with the cold dark matter paradigm so long as they are attained at sufficiently early times. In particular, the predicted recoil velocities are robustly compatible with observations if the remnants form before the epoch of big bang nucleosynthesis, a requirement which is already imposed by the physics of nucleosynthesis itself.

Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy

Observations have found black holes spanning 10 orders of magnitude in mass across most of cosmic history. The Kerr black hole solution is, however, provisional as its behavior at infinity is incompatible with an expanding universe. Black hole models with realistic behavior at infinity predict that the gravitating mass of a black hole can increase with the expansion of the universe independently of accretion or mergers, in a manner that depends on the black hole’s interior solution. We test this prediction by considering the growth of supermassive black holes in elliptical galaxies over 0 < z ≲ 2.5. We find evidence for cosmologically coupled mass growth among these black holes, with zero cosmological coupling excluded at 99.98% confidence. The redshift dependence of the mass growth implies that, at z ≲ 7, black holes contribute an effectively constant cosmological energy density to Friedmann’s equations. The continuity equation then requires that black holes contribute cosmologically as vacuum energy. We further show that black hole production from the cosmic star formation history gives the value of ΩΛ measured by Planck while being consistent with constraints from massive compact halo objects. We thus propose that stellar remnant black holes are the astrophysical origin of dark energy, explaining the onset of accelerating expansion at z ∼ 0.7.