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Aretaios Lalakos

Publications and source records attributed to Aretaios Lalakos.

9 recordsLinked to original sources

AGN Jets from Formation to Dissipation

Active Galactic Nuclei (AGN) are among the most energetic phenomena in the Universe, capable of launching powerful relativistic jets that extend from sub-parsec to megaparsec scales. These jets play a crucial role in regulating star formation, redistributing energy and matter, and shaping the evolution of galaxies and their environments. Despite decades of study, a comprehensive understanding of how AGN jets form, propagate, and dissipate remains elusive. The aim of this chapter is to highlight how the future capabilities of the the Square Kilometre Array (SKA), as a standalone array as well as in combination with Very Long Baseline Interferometry (VLBI) arrays and multi-wavelength facilities, will transform our capabilities to study the co-evolution of AGN jets and their host galaxies from jet formation to dissipation scales.

astro-ph.GA↗

Atacama Cosmology Telescope: Observations of supermassive black hole binary candidates. Strong sinusoidal variations at 95, 147 and 225 GHz in PKS 2131$-$021 and PKS J0805$-$0111

Large sinusoidal variations in the radio light curves of the blazars PKS J0805$-$0111 and PKS 2131$-$021 have recently been discovered with an 18-year monitoring programme at the Owens Valley Radio Observatory, making these systems strong supermassive black hole binary (SMBHB) candidates. The sinusoidal variations in PKS 2131$-$021 dominate its light curves from 2.7 GHz to optical frequencies. We report sinusoidal variations observed in both objects with the Atacama Cosmology Telescope (ACT) at 95, 147 and 225 GHz consistent with the radio light curves. The ACT 95 GHz light curve of PKS 2131$-$021 agrees well with the contemporaneous 91.5 GHz ALMA light curve and is comparable in quality, while the ACT light curves of PKS J0805$-$0111, for which there are no ALMA or other millimetre light curves, show that PKS 2131$-$021 is not an isolated case, and that this class of AGN exhibits the following properties: (a) the sinusoidal pattern dominates over a broad range of frequencies; (b) the amplitude of the sine wave compared to its mean value is monochromatic (i.e., nearly constant across frequencies); (c) the phase of the sinusoid phase changes monotonically as a function of frequency; (d) the sinusoidal variations are intermittent. We describe a physical model for SMBHB systems, the modified Kinetic Orbital model, that explains all four of these phenomena. Monitoring of ${\sim}8000$ blazars by the Simons Observatory over the next decade should provide a large number of SMBHB candidates that will shed light on the nature of the nanohertz gravitational-wave background.

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Universal Radial Scaling of Large-Scale Black Hole Accretion for Magnetically Arrested And Rocking Accretion Disks

Accretion onto supermassive black holes (BHs) can launch relativistic jets that inject energy and momentum into their surroundings. Understanding how such feedback shapes large-scale accretion is key to bridging observations from galactic scales (e.g., the Bondi radius, $r_{\rm B}$) down to event horizon scales ($r_{\rm g}$), spanning 5-6 orders of magnitude. We tackle this challenge by varying the spatial scale separation across 2-4 orders of magnitude and performing some of the longest contiguous 3D general relativistic magnetohydrodynamic (GRMHD) simulations to date ($t \lesssim 4\times10^6 r_{\rm g}/c$), of Bondi-like accretion of rotating, non-relativistic gas with weak vertical magnetic fields onto a rapidly spinning BH, achieving inflow equilibrium out to $r \gtrsim 10^3 r_{\rm g}$. We find that, regardless of scale separation or ambient gas rotation, all simulations reach a magnetically arrested disk (MAD) state where the BH becomes magnetically saturated. In this state, the mass inflow rate follows a universal radial scaling: $\dot{M}_{\rm in}(r) \sim r^s$ with $s = 0.66 \pm 0.03$. The MAD state self-regulates through jets, outflows, and magnetic flux eruptions that can disrupt coherent angular momentum inflow, giving rise to a rocking accretion disk (RAD) state. This RAD state features chaotically oriented inflows, weak intermittent jets, and a steeper inflow slope of $s = 0.87 \pm 0.05$. The MAD and RAD BH accretion rates become comparable at typical scale separations, $r_{\rm B}/ r_{\rm g} \gtrsim 10^5$. Weaker RAD outflows allow large-scale inflows to resume, restoring the MAD state and enabling a recurring MAD-RAD cycle. These cycles can last tens of Bondi timescales, $t_{\rm B} \sim 0.2\,\text{Myr} \times (r_{\rm B}/10^{5} r_{\rm g})^{3/2} \times (M_{\rm BH}/10^9M_\odot)$, potentially setting the duty cycle of jetted AGN outbursts, such as in M87*.

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Galactic-scale Feeding Reveals Warped Hypermagnetized Multiphase Circumbinary Accretion Around Supermassive Black Hole Binaries

Supermassive black hole (SMBH) binaries in gaseous and stellar environments are prime targets for next-generation space-based gravitational wave detectors. Yet, realistic accretion conditions under which these binary systems evolve are not fully understood. In this work, we demonstrate the hypermagnetized multi-phase nature of the surrounding accretion flow formed by large-scale feeding from a galaxy background. Our simulations indicate that the hypermagnetized circumbinary disk is eccentric and warped, hosting a hot gas core for a parsec-scale separated binary. We also observe collimated bipolar magnetic tower-like outflows launched from each SMBH.

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How to Turn Jets into Cylinders near Supermassive Black Holes in 3D GRMHD Simulations

Accreting supermassive black holes (SMBHs) produce highly magnetized relativistic jets that tend to collimate gradually as they propagate outward. However, recent radio interferometric observations of the 3C 84 galaxy reveal a stunning, cylindrical jet already at several hundred SMBH gravitational radii, $r\gtrsim350r_{\rm g}$. We explore how such extreme collimation emerges via a suite of 3D general-relativistic magnetohydrodynamic (GRMHD) simulations. We consider an SMBH surrounded by a magnetized torus immersed in a constant-density ambient medium that starts at the edge of the SMBH sphere of influence, chosen to be much larger than the SMBH gravitational radius, $r_{\text{B}}=10^3r_{\text{g}}$. We find that radiatively inefficient accretion flows (e.g., M87) produce winds that collimate the jets into parabolas near the BH. After the disk winds stop collimating the jets at $r\lesssim{}r_\text{B}$, they turn conical. Once outside $r_\text{B}$, the jets run into the ambient medium and form backflows that collimate the jets into cylinders some distance beyond $r_{\text{B}}$. Interestingly, for radiatively-efficient accretion, as in 3C 84, the radiative cooling saps the energy out of the disk winds: at early times, they cannot efficiently collimate the jets, which skip the initial parabolic collimation stage, start out conical near the SMBH, and turn into cylinders already at $r\simeq300r_{\rm g}$, as observed in 3C 84. Over time, jet power remains approximately constant, whereas the mass accretion rate increases: the winds grow in strength and start to collimate the jets, which become quasi-parabolic near the base; the transition point to a nearly cylindrical jet profile moves outward while remaining inside $r_\text{B}$.

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Jets with a Twist: Emergence of FR0 Jets in 3D GRMHD Simulation of Zero Angular Momentum Black Hole Accretion

Spinning supermassive black holes (BHs) in active galactic nuclei (AGN) magnetically launch relativistic collimated outflows, or jets. Without angular momentum supply, such jets are thought to perish within $3$ orders of magnitude in distance from the BH, well before reaching kpc-scales. We study the survival of such jets at the largest scale separation to date, via 3D general relativistic magnetohydrodynamic simulations of rapidly spinning BHs immersed into uniform zero-angular-momentum gas threaded by weak vertical magnetic field. We place the gas outside the BH sphere of influence, or the Bondi radius, chosen much larger than the BH gravitational radius, $R_\text{B}=10^3R_\text{g}$. The BH develops dynamically-important large-scale magnetic fields, forms a magnetically-arrested disk (MAD), and launches relativistic jets that propagate well outside $R_\text{B}$ and suppress BH accretion to $1.5\%$ of the Bondi rate, $\dot{M}_\text{B}$. Thus, low-angular-momentum accretion in the MAD state can form large-scale jets in Fanaroff-Riley (FR) type I and II galaxies. Subsequently, the disk shrinks and exits the MAD state: barely a disk (BAD), it rapidly precesses, whips the jets around, globally destroys them, and lets $5-10\%$ of $\dot{M}_\text{B}$ reach the BH. Thereafter, the disk starts rocking back and forth by angles $90-180^\circ$: the rocking accretion disk (RAD) launches weak intermittent jets that spread their energy over a large area and suppress BH accretion to $\lesssim 2 \% ~ \dot{M}_\text{B}$. Because BAD and RAD states tangle up the jets and destroy them well inside $R_\text{B}$, they are promising candidates for the more abundant, but less luminous, class of FR0 galaxies.

astro-ph.HE↗

Black hole to photosphere: 3D GRMHD simulations of collapsars reveal wobbling and hybrid composition jets

Long-duration $γ$-ray bursts (GRBs) accompany the collapse of massive stars and carry information about the central engine. However, no 3D models have been able to follow these jets from their birth by a black-hole (BH) to the photosphere. We present the first such 3D general-relativity magnetohydrodynamic simulations, which span over 6 orders of magnitude in space and time. The collapsing stellar envelope forms an accretion disk, which drags inwardly the magnetic flux that accumulates around the BH, becomes dynamically important and launches bipolar jets. The jets reach the photosphere at $\sim10^{12}$ cm with an opening angle $θ_j\sim6^\circ$ and a Lorentz factor $Γ_j\lesssim 30$, unbinding $\gtrsim90\%$ of the star. We find that (i) the disk-jet system spontaneously develops misalignment relative to the BH rotational axis. As a result, the jet wobbles with an angle $θ_t\sim12^\circ$, which can naturally explain quiescent times in GRB lightcurves. The effective opening angle for detection $θ_j+θ_t$ suggests that the intrinsic GRB rate is lower by an order of magnitude than standard estimates. This suggests that successful GRBs may be rarer than currently thought and emerge in only $\sim 0.1\%$ of supernovae Ib/c, implying that jets are either not launched or choked inside most supernova Ib/c progenitors. (ii) The magnetic energy in the jet decreases due to mixing with the star, resulting in jets with a hybrid composition of magnetic and thermal components at the photosphere, where $\sim 10\%$ of the gas maintains magnetization $σ\gtrsim 0.1$. This indicates that both a photospheric component and reconnection may play a role in the prompt emission.

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Bridging Bondi and Event Horizon Scales: 3D GRMHD Simulations Reveal X-Shaped Radio Galaxy Morphology

X-shaped radio galaxies (XRGs) produce misaligned X-shaped jet pairs and make up $\lesssim10\%$ of radio galaxies. XRGs are thought to emerge in galaxies featuring a binary supermassive black hole ($\rm SMBH$), $\rm SMBH$ merger, or large-scale ambient medium asymmetry. We demonstrate that XRG morphology can naturally form without such special, preexisting conditions. Our 3D general-relativistic magnetohydrodynamic (GRMHD) simulation for the first time follows magnetized rotating gas from outside the $\rm SMBH$ sphere of influence of radius $R_{\rm B}$ to the $\rm SMBH$ of gravitational radius $R_{\rm g}$, at the largest scale separation $R_{\rm B}/R_{\rm g} = 10^3$ to date. Initially, our axisymmetric system of constant-density hot gas contains weak vertical magnetic field and rotates in an equatorial plane of a rapidly spinning $\rm SMBH$. We seed the gas with small-scale $2\%$-level pressure perturbations. Infalling gas forms an accretion disk, and the $\rm SMBH$ launches relativistically-magnetized collimated jets reaching well outside $R_{\rm B}$. Under the pressure of the infalling gas, the jets intermittently turn on and off, erratically wobble, and inflate pairs of cavities in different directions, resembling an X-shaped jet morphology. Synthetic X-ray images reveal multiple pairs of jet-powered shocks and cavities. Large-scale magnetic flux accumulates on the $\rm SMBH$, becomes dynamically important, and leads to a magnetically arrested disk state. The $\rm SMBH$ accretes at $2\%$ of the Bondi rate ($\dot{M}\simeq2.4\times10^{-3}M_{\odot}\,{\rm yr}^{-1}$ for M87*), and launches twin jets at $η=150\%$ efficiency. These jets are powerful enough ($P_{\rm jets}\simeq2\times10^{44}\,{\rm erg\,s}^{-1}$) to escape along the spin axis and end the short-lived jets state whose transient nature can account for the rarity of XRGs

astro-ph.HE↗

Black hole to breakout: 3D GRMHD simulations of collapsar jets reveal a wide range of transients

We present a suite of the first 3D GRMHD collapsar simulations, which extend from the self-consistent jet launching by an accreting Kerr black hole (BH) to the breakout from the star. We identify three types of outflows, depending on the angular momentum, $ l $, of the collapsing material and the magnetic field, $ B $, on the BH horizon: (i) Subrelativistic outflow (low $ l $ and high $ B $), (ii) Stationary accretion shock instability (SASI; high $ l $ and low $ B $), (iii) Relativistic jets (high $ l $ and high $ B $). In the absence of jets, free-fall of the stellar envelope provides a good estimate for the BH accretion rate. Jets can substantially suppress the accretion rate, and their duration can be limited by the magnetization profile in the star. We find that progenitors with large (steep) inner density power-law indices ($ \gtrsim 2 $), face extreme challenges as gamma-ray burst (GRB) progenitors due to excessive luminosity, global time evolution in the lightcurve throughout the burst and short breakout times, inconsistent with observations. Our results suggest that the wide variety of observed explosion appearances (supernova/supernova+GRB/low-luminosity GRBs) and the characteristics of the emitting relativistic outflows (luminosity and duration) can be naturally explained by the differences in the progenitor structure. Our simulations reveal several important jet features: (i) strong magnetic dissipation inside the star, resulting in weakly magnetized jets by breakout that may have significant photospheric emission and (ii) spontaneous emergence of tilted accretion disk-jet flows, even in the absence of any tilt in the progenitor.

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