Black hole rhythms unveiled

We study the compact binary population in star clusters, focusing on binaries containing black holes, using a self-consistent Monte Carlo treatment of dynamics and full stellar evolution. We find that the black holes experience strong mass segregation and become centrally concentrated. In the core the black holes interact strongly with each other and black hole-black hole binaries are formed very efficiently. The strong interactions, however, also destroy or eject the black hole-black hole binaries. We find no black hole-black hole mergers within our simulations but produce many hard escapers that will merge in the galactic field within a Hubble time. We also find several highly eccentric black hole-black hole binaries that are potential LISA sources, suggesting that star clusters are interesting targets for space-based detectors. We conclude that star clusters must be taken into account when predicting compact binary population statistics.

<p><strong>The future of theoretical physics is unclear. Two large areas that fall under the umbrella of theoretical physics are cosmology and quantum gravity. Modern cosmology is relatively a much younger field than quantum gravity, and both of these fields require further developments of general relativity. In this thesis we do not hope to resolve the problems facing modern cosmology or theories of quantum gravity. Rather, we will conduct original research into aspects of general relativity that may be used in the future to aid the development and testing of theories of cosmology and quantum gravity.</strong></p><p>It is our view that the largest problem facing astrophysics and cosmology stem from the existence of the dark sector of the Universe. The implication here being that more than ninety percent of the energy density of the Universe is “missing in action” and seemingly consists of dark energy and dark matter. Furthermore, it is apparent that there exist conceptual flaws in our understanding of observational concepts such as expansion versus motion and observer biases. To this end, we investigate the standard spacetime metric used in cosmology, the Friedmann–Lemaˆıtre-Roberston–Walker (FLRW) metric in a peculiar coordinate system — the Painlev´e–Gullstrand coordinates. In this coordinate system (slicing), space is no longer expanding, rather, the galaxies are receding from each other. We hope this will aid in the understanding of expansion, motion, curvature, and observer bias with future work. We further investigate the possibility of black holes in cosmology being directly coupled to the accelerated expansion of the Universe — in other words, black holes as a source for dark energy. However, we show that this is highly implausible.</p><p>Relatively recently it has been postulated that the near black hole horizon limit may be a regime where quantum gravity effects become relevant i.e., quantum gravity may not be restricted to near the Planck scale. We investigate a curious model of black and white holes that shows how one may transition into the other over a finite period of time. This is research conducted in the near horizon limit of the Schwarzschild black hole. We introduce a time dependent function into the usual Schwarzschild black hole spacetime (leaving this new spacetime not a simple coordinate transformed version of the original). This function allows the black hole to transition into a white hole. Importantly, the action for this transition can be shown to be zero, meaning it can be added to the Feynman path integral at no cost.</p><p>Finally, we move to investigating the black hole memory effect. During the last decade, there has been an interesting connection made between the Bondi– Metzner–Sachs (BMS) group — an infinite dimensional group of symmetries found at null infinity — and the gravitational memory effect. In particular, it was shown that the passage of a gravitational wave that alters a Schwarzschild black hole is seen as a supertranslation of the spacetime at null infinity. We extend these calculations to the Kerr and Kerr–Newman black holes. Hence, showing that there may be a way to verify the abstract mathematical ideas predicated on the BMS group by detection of the memory effect in future observations.</p><p>It is our hope that when future gravitational wave detectors such as the laser-interferometer-space-antenna (LISA) are launched, research conducted in this thesis may shed light on how the memory may relate to black holes in their asymptotic & near horizon limits to aid our understanding of the nature of quantum gravity.</p>

Modern models predict that galaxies do not evolve in isolation, but exist in haloes of dark matter and gas, embedded in the large-scale cosmic web. To build a self-consistent model for how galaxies form and evolve, it is vital to understand how galaxies regulate their formation through interaction with the circumgalactic medium that surrounds them, and at present the nature and impact of these interactions is poorly-constrained by both theory and observations. This thesis presents new insights into how galaxies affect their surroundings through feedback processes, the impact of the properties of the CGM on galaxy evolution, and how the properties of galaxy-CGM ecosystems are fundamentally connected to the assembly histories of their dark matter haloes. I begin by examining the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day ~L* central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy's black hole (BH), but correlates strongly and negatively with the BH's mass, implicating differences in the expulsion of gas by active galactic nucleus (AGN) feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit elevated star formation rates (SFRs). Diversity in the mass of central BHs stems primarily from diversity in the dark matter halo binding energy, as these quantities are strongly and positively correlated at fixed halo mass, such that ~L* galaxies hosted by haloes that are more (less) tightly-bound develop central BHs that are more (less) massive than is typical for their halo mass. Variations in the halo gas fraction at fixed halo mass are reflected in both the soft X-ray luminosity and thermal Sunyaev-Zel'dovich flux, suggesting that the prediction of a strong coupling between the properties of galaxies and their halo gas fractions can be tested with measurements of these diagnostics for galaxies with diverse SFRs but similar halo masses. I then examine the connection between the properties of the CGM and the quenching and morphological evolution of central galaxies in both the EAGLE and IllustrisTNG simulations. The simulations yield very different median CGM mass fractions as a function of halo mass, with low-mass haloes being significantly more gas-rich in IllustrisTNG than in EAGLE. Nonetheless, in both cases the scatter in the CGM mass fraction at fixed halo mass is strongly correlated with the specific star formation rate and the kinematic morphology of central galaxies. This feedback elevates the CGM cooling time, preventing gas from accreting onto the galaxy to fuel star formation, and thus establishing a preference for quenched, spheroidal galaxies to be hosted by haloes with low CGM mass fractions for their mass. In both simulations, the CGM mass fraction correlates negatively with the host halo's intrinsic concentration, and hence with its binding energy and formation redshift, primarily because early halo formation fosters the rapid early growth of the central black hole (BH). This leads to a lower CGM mass fraction at fixed halo mass in EAGLE because the BH reaches high accretion rates sooner, whilst in IllustrisTNG it occurs because the central BH reaches the mass threshold at which AGN feedback is assumed to switch from thermal to kinetic injection earlier. Despite these differences, there is consensus from these state-of-the-art simulations that the expulsion of efficiently-cooling gas from the CGM is a crucial step in the quenching and morphological evolution of central galaxies. The above results suggest a connection between the assembly histories of dark matter haloes and the properties of their galaxy-CGM ecosystems. I clearly demonstrate this connection by performing a controlled and systematic experiment in which I adjust the assembly history of a single EAGLE halo hosting a moderately star-forming Milky Way-like galaxy by ``genetically modifying its initial conditions, keeping all other variables fixed. Shifting the halo assembly history to earlier times increases the integrated feedback injected by the AGN, ejecting a greater fraction of the CGM baryons and leading to the quenching and morphological transformation of the central galaxy. These effects can only have originated from differences in the assembly history of the halo, providing compelling evidence for this novel picture of the self-regulation of galaxy formation.

In this paper, we study a proposal put forward recently by Bodendorfer, Mele and Münch and García-Quismondo and Marugán, in which the two polymerization parameters of spherically symmetric black hole spacetimes are the Dirac observables of the four-dimensional Ashtekar’s variables. In this model, black and white hole horizons in general exist and naturally divide the spacetime into the external and internal regions. In the external region, the spacetime can be made asymptotically flat by properly choosing the dependence of the two polymerization parameters on the Ashtekar variables. Then, we find that the asymptotical behavior of the spacetime is universal, and, to the leading order, the curvature invariants are independent of the mass parameter m. For example, the Kretschmann scalar approaches zero as K≃A0r−4 asymptotically, where A0 is generally a non-zero constant and independent of m, and r the geometric radius of the two-spheres. In the internal region, all the physical quantities are finite, and the Schwarzschild black hole singularity is replaced by a transition surface whose radius is always finite and non-zero. The quantum gravitational effects are negligible near the black hole horizon for very massive black holes. However, the behavior of the spacetime across the transition surface is significantly different from all loop quantum black holes studied so far. In particular, the location of the maximum amplitude of the curvature scalars is displaced from the transition surface and depends on m; so does the maximum amplitude. In addition, the radius of the white hole is much smaller than that of the black hole, and its exact value sensitively depends on m, too.

We discuss the macroscopic quantum tunneling from the black hole to the white hole of the same mass. Previous calculations in [G. E. Volovik, Universe 6, 133 (2020)] demonstrated that the probability of the tunneling is [Formula: see text], where [Formula: see text] is the entropy of the Schwarzschild black hole. This in particular suggests that the entropy of the white hole is with minus sign the entropy of the black hole, [Formula: see text]. Here, we use a different way of calculations. We consider three different types of the hole objects: black hole, white hole and the fully static intermediate state. The probability of tunneling transitions between these three states is found using singularities in the coordinate transformations between these objects. The black and white holes are described by the Painleve–Gullstrand coordinates with opposite shift vectors, while the intermediate state is described by the static Schwarzschild coordinates. The singularities in the coordinate transformations lead to the imaginary part in the action, which determines the tunneling exponent. For the white hole the same negative entropy is obtained, while the intermediate state — the fully static hole — has zero entropy. This procedure is extended to the Reissner–Nordström black hole and to its white and static partners, and also to the entropy and temperature of the de Sitter Universe.

Bridging the gap between the approximately ten solar mass 'stellar mass' black holes and the 'supermassive' black holes of millions to billions of solar masses are the elusive 'intermediate-mass' black holes. Their discovery is key to understanding whether supermassive black holes can grow from stellar-mass black holes or whether a more exotic process accelerated their growth soon after the Big Bang. Currently, tentative evidence suggests that the progenitors of supermassive black holes were formed as ∼10(4)-10(5) M(⊙) black holes via the direct collapse of gas. Ongoing searches for intermediate-mass black holes at galaxy centres will help shed light on this formation mechanism.

In a space with fixed positive cosmological constant Λ, we consider a system with a black hole surrounded by a heat reservoir at radius R and fixed temperature T, i.e., we analyze the Schwarzschild–de Sitter black hole space in a cavity. We use results from the Euclidean path integral approach to quantum gravity to study, in a semiclassical approximation, the corresponding canonical ensemble and its thermodynamics. We give the action for the Schwarzschild–de Sitter black hole space and calculate expressions for the thermodynamic energy, entropy, temperature, and heat capacity. The reservoir radius R gauges the other scales. Thus, the temperature T, the cosmological constant Λ, the black hole horizon radius r+, and the cosmological horizon radius rc, are gauged to RT, ΛR2, r+R, and rcR. The whole extension of ΛR2, 0≤ΛR2≤3, can be split into three ranges. The first range, 0≤ΛR2<1, includes York’s pure Schwarzschild black holes. The other values of ΛR2 within this range also have black holes. The second range, ΛR2=1, opens up a folder containing Nariai universes, rather than black holes. The third range, 1<ΛR2≤3, is unusual. One striking feature here is that it interchanges the cosmological horizon with the black hole horizon. The end of this range, ΛR2=3, only existing for infinite temperature, represents a cavity filled with de Sitter space inside, except for a black hole with zero radius, i.e., a singularity, and with the cosmological horizon coinciding with the reservoir radius. For the three ranges, for sufficiently low temperatures, which for quantum systems involving gravitational fields can be very high when compared to normal scales, there are no black hole solutions and no Nariai universes, and the space inside the reservoir is hot de Sitter. The limiting value RT that divides the nonexistence from existence of black holes or Nariai universes, depends on the value of ΛR2. For each ΛR2 different from one, for sufficiently high temperatures there are two black holes, one small and thermodynamically unstable, and one large and stable. For ΛR2=1, for any sufficiently high temperature there is the small unstable black hole, and the neutrally stable hot Nariai universe. Phase transitions can be analyzed, the dominant phase has the least action. The transitions are between Schwarzschild-de Sitter black hole and hot de Sitter phases and between Nariai and hot de Sitter. For small cosmological constant, the action for the stable black hole equals the pure de Sitter action at a certain black hole radius and temperature, and so the phases coexist equally. For 0<ΛR2<1 the equal action black hole radius is smaller than the Buchdahl radius, the radius for total collapse, and the corresponding Buchdahl temperature is greater than the equal action temperature. So above the Buchdahl temperature, the system collapses and the phase is constituted by a black hole. For ΛR2≥1 a phase analysis is also made. Published by the American Physical Society 2024

Aims. It is speculated that a merger of two massive stellar-origin black holes in a dense stellar environment may lead to the formation of a massive black hole in the pair-instability mass gap (∼50−135 M⊙). Such a merger-formed black hole is expected to typically have a high spin (a ∼ 0.7). If such a massive black hole acquires another black hole it may lead to another merger detectable by LIGO/Virgo in gravitational waves. Acquiring a companion may be hindered by gravitational-wave kick/recoil, which accompanies the first merger and may quickly remove the massive black hole from its parent globular or nuclear cluster. We test whether it is possible for a massive merger-formed black hole in the pair-instability gap to be retained in its parent cluster and have low spin. Such a black hole would be indistinguishable from a primordial black hole. Methods. We employed results from numerical relativity calculations of black hole mergers to explore the range of gravitational-wave recoil velocities for various combinations of merging black hole masses and spins. We compared merger-formed massive black hole speeds with typical escape velocities from globular and nuclear clusters. Results. We show that a globular cluster is highly unlikely to form and retain a ∼100 M⊙ black hole if the spin of the black hole is low (a ≲ 0.3). Massive merger-formed black holes with low spins acquire high recoil speeds (≳ 200 km s−1) from gravitational-wave kick during formation that exceed typical escape speeds from globular clusters (∼ 50 km s−1). However, a very low-spinning (a ∼ 0.1) and massive (∼100 M⊙) black hole could be formed and retained in a galactic nuclear star cluster. Even though such massive merger-formed black holes with such low spins acquire high speeds during formation (∼ 400 km s−1), they may avoid ejection since massive nuclear clusters have high escape velocities (∼ 300−500 km s−1). A future detection of a massive black hole in the pair-instability mass gap with low spin would therefore not be proof of the existence of primordial black holes, which are sometimes claimed to have low spins and arbitrarily high masses.

ABSTRACTWe present the evolution of black holes (BHs) and their relationship with their host galaxies in Astrid, a large-volume cosmological hydrodynamical simulation with box size 250 h−1Mpc containing 2 × 55003 particles evolved to z = 3. Astrid statistically models BH gas accretion and active galactic nucleus (AGN) feedback to their environments, applies a power-law distribution for BH seed mass $\, M_{\rm sd}$, uses a dynamical friction model for BH dynamics, and executes a physical treatment of BH mergers. The BH population is broadly consistent with empirical constraints on the BH mass function, the bright end of the luminosity functions, and the time evolution of BH mass and accretion rate density. The BH mass and accretion exhibit a tight correlation with host stellar mass and star formation rate. We trace BHs seeded before z > 10 down to z = 3, finding that BHs carry virtually no imprint of the initial $\, M_{\rm sd}$ except those with the smallest $\, M_{\rm sd}$, where less than 50 per cent of them have doubled in mass. Gas accretion is the dominant channel for BH growth compared to BH mergers. With dynamical friction, Astrid predicts a significant delay for BH mergers after the first encounter of a BH pair, with a typical elapse time of about 200 Myr. There are in total 4.5 × 105 BH mergers in Astrid at z > 3, ∼103 of which have X-ray detectable EM counterparts: a bright $\, {\rm kpc}$ scale dual AGN with LX > 1043 erg s−1. BHs with $\, M_{\rm BH}\sim 10^{7\!-\!8} \, M_{\odot }$ experience the most frequent mergers. Galaxies that host BH mergers are unbiased tracers of the overall $\, M_{\rm BH}\!-\! M_*$ relation. Massive ($\gt 10^{11}\, M_{\odot }$) galaxies have a high occupation number (≳10) of BHs, and hence host the majority of BH mergers.

Gadolinium-enhanced T1-weighted lesions are a well-established marker of areas with acute inflammatory activity. A majority of these gadolinium-enhanced T1 lesions are isointense relative to the surrounding white matter, but 20-40% of such active lesions will evolve during one year into areas of low signal ("black hole"). This study sought to characterize evolution of "black hole" lesions in patients with relapsing-remitting multiple sclerosis (MS) using the magnetic resonance imaging (MRI), which measures active lesions via the count of new or enlarged T2 and gadolinium-enhanced T1-weighted lesions. This was a prospective, observational case-series study which utilized pre- and post-gadolinium contrast T1-weighted and Proton density MRI scans. Twenty-nine patients (8 males and 21 females) with average age of 38.86 ± 6.58years and disease duration of 5.75 ± 7.00years were used to analyze 196 acute demyelinating plaques detected on MRI images during the 24-month follow-up of post-gadolinium signal intensity enhancement of MS plaques. Significant difference in black hole development was found between the shapes of acute and chronic "black holes". Ring-shaped and patchy plaques were 4.09 (1.87-8.91) times more likely and 1.49 (0.71-3.12) times less likely to develop an acute "black holes" than homogeneous plaques, respectively. Acute plaques with higher lesion-to-CSF SI ratio and larger surface area showed a greater tendency to develop into acute and chronic "black holes". The value of lesion-to-CSF SI ratio and surface area were found as the predictors of the "black hole" formation.

The dramatic relativistic jets pointing directly at us in BL Lac objects can be well modelled by bulk motion beaming of synchrotron self-Compton emission powered by a low Eddington fraction accretion flow. Nearly 500 of these AGN are seen in the 2nd Fermi Large Area Telescope catalogue of AGN. We combine the jet models which describe individual spectra with the expected jet parameter scalings with mass and mass accretion rate to predict the expected number of Fermi detected sources given the number densities of AGN from cosmological simulations. We select only sources with Eddington scaled mass accretion rate $< 0.01$ (i.e. radiatively inefficient flows), and include cooling, orientation effects, and the effects of absorption from pair production on the extragalactic IR background. These models overpredict the number of Fermi detected BL Lacs by a factor of 1000! This clearly shows that one of the underlying assumptions is incorrect, almost certainly that jets do not scale simply with mass and accretion rate. The most plausible additional parameter which can affect the region producing the Fermi emission is black hole spin. We can reproduce the observed numbers of BL Lacs if such relativistic jets are only produced by the highest spin ($a_*>0.8$) black holes, in agreement with the longstanding spin-jet paradigm. This also requires that high spins are intrinsically rare, as predicted by the cosmological simulations for growing black hole mass via chaotic (randomly aligned) accretion episodes, where only the most massive black holes have high spin due to black hole-black hole mergers.

Observations with the James Webb Space Telescope of massive galaxies at redshift z up to $ ∼ 14$, many of which have quasar activity, require careful accounting of the orbital migration of seed black holes to the heart of the host galaxy on timescales of $300 Myr $ or less. We investigate the circumstances that allow a black hole to remain at the barycentre of a system when the equilibrium galactic stellar core is anisotropic. Edit OK? It's generally best to use active voice.*** We developed a Fokker-Planck treatment to analyse the migration of a massive black hole. The analysis focuses on exchanges of a black hole’s orbital angular momentum with stars. Furthermore, we used a set of N-body calculations to study the response of stellar orbits drawn from a Miyamoto-Nagai disc embedded in a larger, isotropic isochrone (Hénon) background potential. When the black hole has little angular momentum initially but orbits in a sea of stars drawn from an odd fE,L_z velocity distribution function, a wake in the stellar density sets in that pulls on the black hole and transfers angular momentum to it. We call For greater clarity, add a noun: We call this X dynamical traction ...*** this transfer `dynamical traction' in contrast with the more familiar Chandrasekhar dynamical friction. We argue that this phenomenon takes place whenever the kinetic energy drawn from fE,L_z has an excess of streaming motion over its (isotropic) velocity dispersion. We illustrate this process for a black hole orbiting in a dynamically warm disc with no sub-structures. We then show that for a dynamically cold disc, the outcome depends on both the orbit of the black hole and that of the stellar sub-structures stemming from a Jeans instability. When the stellar clumps have much binding energy, a black hole may scatter off of them after they are formed. In the process, the black hole may be dislodged from the centre and migrate outward due to dynamical traction. When the stellar clumps are less bound, they may still migrate to the centre, where they either dissolve or merge with the black hole. The final configuration is similar to a nuclear star cluster that may yet be moving at ∼ 10 ̨ms with regard to the barycentre of the system. The angular momentum transferred to a black hole by dynamical traction delays the migration to the galactic centre by several hundred million years. The efficiency of angular momentum transfer is a strong function of the fragmented (cold) state of the stellar space density. In a dynamically cold environment, a black hole is removed from the central region through a two-stage orbital migration instability. A criterion against this instability is proposed in the form of a threshold in isotropic velocity dispersion compared to streaming motion (i.e. angular momentum). For a black hole to settle at the heart of a galaxy on timescales of ∼ 300 Myr or less, a large fraction of the system angular momentum must be dissipated or, alternatively, the black hole must grow in situ in an isotropic environment devoid of massive sub-structures.

The central region of the galaxy Henize 2-10 has a central black hole (BH) with a mass of about $2\times 10^6$ M$_\odot$. While this black hole does not appear to coincide with any central stellar over density, it is surrounded by 11 young massive clusters with masses above $10^5$ M$_\odot$. The availability of high quality data on the structure of the galaxy and the age and mass of the clusters provides excellent initial conditions for studying the dynamical evolution of Henize 2-10's nucleus. Here we present a set of $N$-body simulations of the central clusters and black hole to understand whether and how they will merge to form a nuclear star cluster. Nuclear star clusters (NSCs) are present in a majority of galaxies with stellar mass similar to Henize 2-10. Despite the results depend on the choice of initial conditions, we find that a NSC with mass $M_{NSC}\simeq 4-6\times 10^6$ M$_\odot$ and effective radius $r_{NSC}\simeq 2.6-4.1$ pc will form within $0.2$ Gyr. This work is the first showing, in a realistic realization of the host galaxy and its star cluster system, that the formation of a bright nucleus is a process that can happen after the formation of a central massive BH leading to a composite NSC+BH central system. The merging process of the clusters does not affect significantly the kinematics of the BH, whose motion, after the globular cluster merger, is limited to a $\sim 1$ pc oscillation at less than $2$ kms$^{-1}$ speed.

Surface photometry is a necessary tool to establish the dynamical state of stars clusters. We produce realistic HST-like images from N-body models of star clusters with and without central intermediate-mass black holes (IMBHs) in order to measure their surface brightness profiles. The models contain ~600,000 individual stars, black holes of various masses between 0% to 2% of the total mass, and are evolved for a Hubble time. We measure surface brightness and star count profiles for every constructed image in order to test the effect of intermediate mass black holes on the central logarithmic slope, the core radius, and the half-light radius. We use these quantities to test diagnostic tools for the presence of central black holes using photometry. We find that the the only models that show central shallow cusps with logarithmic slopes between -0.1 and -0.4 are those containing central black holes. Thus, the central logarithmic slope seems to be a good way to choose clusters suspect of containing intermediate-mass black holes. Clusters with steep central cusps can definitely be ruled out to host an IMBH. The measured r_c/r_h ratio has similar values for clusters that have not undergone core-collapse, and those containing a central black hole. We notice that observed Galactic globular clusters have a larger span of values for central slope and r_c/r_h than our modeled clusters, and suggest possible reasons that could account for this and contribute to improve future models.

A suggested model for quasi-periodic eruptions (QPEs) from galaxy nuclei invokes a white dwarf in an eccentric orbit about the central massive black hole. I point out that the extreme mass ratio allows the presence of strong Lindblad resonances in the accretion disc. These are important for the stability of mass transfer and may trigger the eruptions themselves by rapidly transferring angular momentum from the accretion disc (which is likely to be eccentric itself) to the orbiting WD companion at pericentre. I consider the effects of von Zeipel–Lidov–Kozai (ZLK) cycles caused by a perturber on a more distant orbit about the central black hole. I show that ZLK cycles can change the orbital periods of QPE systems on time-scales much shorter than the mass transfer time, as seen in ASASSN-14ko, and produce correlated short-term variations of their mass transfer rates and orbital periods, as recently observed in GSN 069. Further monitoring of these sources should constrain the parameters of any perturbing companions. This, in turn, may constrain the nature of the events creating QPE systems and perhaps give major insights into how the central black holes in low-mass galaxies are able to grow.