M87 Jet Research Articles

The Faraday Rotation Measure of the M87 Jet at 3.5 mm with ALMA

Faraday rotation is an important probe of the magnetic fields and magnetized plasma around active galactic nuclei jets. We present a Faraday rotation measure (RM) image of the M87 jet between 85.2 and 101.3 GHz with a resolution of ∼2″ with the Atacama Large Millimeter/submillimeter Array. We found that the RM of the M87 core is (4.5 ± 0.4) × 104 rad m−2 with a low linear polarization fraction of (0.88 ± 0.08)%. The spatial RM gradient in the M87 jet spans a wide range from ∼ −2 × 104 rad m−2 to ∼3 × 104 rad m−2 with a typical uncertainty of 0.3 × 104 rad m−2. A comparison with previous RM measurements of the core suggests that the Faraday rotation of the core may originate very close to the supermassive black hole. Both an internal origin and an external screen with a rapidly varying emitting source could be possible. As for the jet, the RM gradient indicates a helical configuration of the magnetic field that persists up to the kiloparsec scale. Combined with the kiloparsec-scale RM measurements at lower frequencies, we found that RM is frequency-dependent in the jet. One possible scenario to explain this dependence is that the kiloparsec-scale jet has a trumpet-like shape, and the jet coil unwinds near its end.

A 9 Month Hubble Space Telescope Near-UV Survey of M87. II. A Strongly Enhanced Nova Rate near the Jet of M87

The 135 classical novae that we have discovered in M87 with two Hubble Space Telescope imaging surveys appear to be strongly concentrated along that galaxy’s jet. Detailed simulations show that the likelihood that this distribution occurred by chance is of order 0.3%. The novae near the jet display outburst characteristics (peak luminosities, colors, and decline rates) that are indistinguishable from novae far from the jet. We explore whether the remarkable nova distribution could be caused by the jet’s irradiation of the hydrogen-rich donors in M87's cataclysmic binaries. This explanation, and others extant in the literature that rely on increased binary mass transfer rates, fail by orders of magnitude in explaining the enhanced nova rate near the jet. An alternate explanation is the presence of a genuine surplus of nova binary systems near the jet, perhaps due to jet-induced star formation. This explanation fails to explain the lack of nova enhancement along M87's counterjet. The enhanced rate of novae along M87's jet is now firmly established, and unexplained.

Jet-induced Enhancement of the Nova Rate in M87

We argue that the Bondi accretion mechanism has the potential to enhance classical nova production near the M87 jet. According to our estimates, the jet's influence can increase the nova rate in its vicinity by up to a factor of two over the background rate by triggering explosions on single white dwarfs. This result may offer a straightforward explanation for the recently observed excess of novae near the M87 jet.

Chandra Study of the Proper Motion of HST-1 in the Jet of M87

The radio galaxy M87 is well known for its jet, which features a series of bright knots observable from radio to X-ray wavelengths. We analyze the X-ray image and flux variability of the knot HST-1 in the jet. Our analysis includes all 112 available Chandra ACIS-S observations from 2000 to 2021, with a total exposure time of ∼884 ks. We use deconvolved images to study the brightness profile of the X-ray jet and measure the relative separation between the core and HST-1. From 2003 to 2005 (which coincides with a bright flare from HST-1), we find a correlation between the flux of HST-1 and its offset from the core. In subsequent data, we find a steady increase in this offset, which implies a bulk superluminal motion for HST-1 of 6.6 ± 0.9 c (2.0 ± 0.3 pc yr−1), in keeping with prior results. We discuss models for the flux–offset correlation that feature either two or four emission regions separated by tens of parsecs. We attribute these results to moving shocks in the jet, which allow us to measure the internal structure of the jet.

Formation of Limb-brightened Radio Jets by Angle-dependent Energy Extraction from Rapidly Rotating Black Holes

Using general relativistic magnetohydrodynamic simulations, it has been suggested that the rotational energy of a rapidly rotating black hole (BH) is preferentially extracted along the magnetic field lines threading the event horizon in the middle and lower latitudes. Applying this angle-dependent Poynting flux to the jet downstream, we demonstrate that the jets exhibit limb-brightened structures at various viewing angles, as observed from Mrk 501, M87, and Cyg A between 5° and 75°, and that the limb brightening is enhanced when the jet is collimated strongly. It is also found that the jet width perpendicular to the propagation direction shrinks at the projected distance of the altitude where the jet collimates from a conical shape (near the BH) to a parabolic one (in the jet). Comparing with Very Long Baseline Interferometry observations, we show that this collimation takes place within the deprojected altitude of 100 Schwarzschild radii from the BH in the case of the M87 jet.

Modeling the inner part of the jet in M87: Confronting jet morphology with theory.

The formation of jets in black hole accretion systems is a long-standing problem. It has been proposed that a jet can be formed by extracting the rotation energy of the black hole ("BZ-jet") or the accretion flow ("disk-jet"). While both models can produce collimated relativistic outflows, neither has successfully explained the observed jet morphology. By using general relativistic magnetohydrodynamic simulations and considering nonthermal electrons accelerated by magnetic reconnection that is likely driven by magnetic eruption in the underlying accretion flow, we obtain images by radiative transfer calculations and compared them to millimeter observations of the jet in M87. We find that the BZ-jet originating from a magnetically arrested disk around a high-spin black hole can well reproduce the jet morphology, including its width and limb-brightening feature.

On the M87 jet structure near the central engine

ABSTRACT At present, there is no doubt that relativistic jets observed in active galactic nuclei pass from highly magnetized to weakly magnetized stage, which is observed as a break in the dependence on their width $d_{\rm jet}(z)$ on the distance z to the central engine. In this paper, we discuss the possibility of observing another break, which should be located at shorter distances. The position of this break can be associated with the region of formation of the dense central core near the jet axis which was predicted both analytically and numerically more than a decade ago, but has not yet received sufficient attention. In this case, the observed width should be determined by the dense core, and not by the total transverse size of the jet. The calculations carried out in this paper, which took into account both the transverse electromagnetic structure of the jet and the change in the spectrum of emitting particles along its axis, indeed showed such behaviour. We also found the evidence of the predicted break in the jet expansion profile using stacked 15 GHz Very Large Baseline Array (VLBA) image of M87 radio jet and constrain the light cylinder radius.

Jump-starting Relativistic Flows and the M87 Jet

We point out the dominant importance of plasma injection effects of relativistic winds from pulsars and black holes. We demonstrate that outside the light cylinder, the magnetically dominated outflows sliding along the helical magnetic field move nearly radially with very large Lorentz factors, γ 0 ≫ 1, imprinted into the flow during pair production within the gaps. Only at larger distances, r ≥ γ 0(c/Ω), does MHD acceleration Γ ∝ r take over. As a result, Blandford–Znajek (BZ)-driven outflows produce spine-brightened images. The best-resolved case of the jet in M87 shows both edge-brightened features, as well as weaker spine-brightened features. Only the spine-brightened component can be BZ driven/originate from the black hole's magnetosphere.

On the comparison of AGN with GRMHD simulations – II. M87

ABSTRACT Horizon-scale observations of the jetted active galactic nucleus M87 are compared with simulations spanning a broad range of dissipation mechanisms and plasma content in three-dimensional general relativistic flows around spinning black holes. Observations of synchrotron radiation from radio to X-ray frequencies can be compared with simulations by adding prescriptions specifying the relativistic electron-plus-positron distribution function and associated radiative transfer coefficients. A suite of time-varying simulations with various spins, plasma magnetizations and turbulent heating and equipartition-based emission prescriptions (and piecewise combinations thereof) is chosen to represent distinct possibilities for the M87 jet/accretion flow/black hole system. Simulation jet morphology, polarization, and variation are then ‘observed’ and compared with real observations to infer the rules that govern the polarized emissivity. Our models support several possible spin/emission model/plasma composition combinations supplying the jet in M87, whose black hole shadow has been observed down to the photon ring at 230 GHz by the Event Horizon Telescope (EHT). Net linear polarization and circular polarization constraints favour magnetically arrested disc (MAD) models whereas resolved linear polarization favours standard and normal evolution (SANE) in our parameter space. We also show that some MAD cases dominated by intrinsic circular polarization have near-linear V/I dependence on un-paired electron or positron content while SANE polarization exhibits markedly greater positron-dependent Faraday effects – future probes of the SANE/MAD dichotomy and plasma content with the EHT. This is the second work in a series also applying the ‘observing’ simulations methodology to near-horizon regions of supermassive black holes in Sgr A* and 3C 279.

Dynamics of M87 jet

AbstractFlows originating from black hole magnetospheres via Blandford-Znajek (BZ) process start highly relativistically, with very large Lorentz factors γ0 1, imprinted into the flow during pair production within the gaps. As a result, BZ-driven outflows would produce spine-brightened images, contrary to observations of the edge-brightened jet in M87. We conclude that M87 jet is not BZ-driven.

Properties of the jet in M87 revealed by its helical structure imaged with the VLBA at 8 and 15 GHz

ABSTRACT We present full-track high-resolution radio observations of the jet of the galaxy M87 at 8 and 15 GHz. These observations were taken over three consecutive days in 2009 May using the Very Long Baseline Array (VLBA), one antenna of the Very Large Array (VLA), and the Effelsberg 100 m telescope. Our produced images have dynamic ranges exceeding 20 000:1 and resolve linear scales down to approximately 100 Schwarzschild radii, revealing a limb-brightened jet and a faint, steep spectrum counter-jet. We performed jet-to-counter-jet analysis, which helped estimate the physical parameters of the flow. The rich internal structure of the jet is dominated by three helical threads, likely produced by the Kelvin–Helmholtz (KH) instability developing in a supersonic flow with a Mach number of approximately 20 and an enthalpy ratio of around 0.3. We produce a clean imaging bias-corrected 8–15 GHz spectral index image, which shows spectrum flattening in regions of helical thread intersections. This further supports the KH origin of the observed internal structure of the jet. We detect polarized emission in the jet at distances of approximately 20 milliarcseconds from the core and find Faraday rotation which follows a transverse gradient across the jet. We apply Faraday rotation correction to the polarization position angle and find that the position angle changes as a function of distance from the jet axis, which suggests the presence of a helical magnetic field.

CLEAN imaging systematics of M87 radio jet

ABSTRACT The spectral index images of the jet in the nearby radio galaxy M87 have previously been shown with Very Long Baseline Interferometric arrays at 2–43 GHz. They exhibit flattening of the spectra at a location of inner (central) spine and towards outer ridges. This could imply optical depth effects, lower energy cut-off, or stratification of the emitting particles energy distribution. In this paper, we employ simulations of multifrequency VLBI observations of M87 radio jet with various model brightness distributions. CLEAN deconvolution errors produce significant features in the observed images. For intensity images, they result in the appearance of the inner ridge line in the intrinsically edge brightened jet models. For spectral index images, they flatten the spectra in a series of stripes along the jet. Another bias encountered in our simulations is steepening of the spectra in a low surface brightness jet regions. These types of the imaging artefacts do not depend on the model considered. We propose a method for the compensation of the systematics using only the observed data.

Robust analysis of differential Faraday rotation based on interferometric closure observables

Polarization calibration of interferometric observations is a costly procedure and in some cases (e.g., due to limited coverage of paral-lactic angle for the calibrator), it may not be possible to carry out this process. To avoid this worst-case scenario, while extending the possibilities for the exploitation of polarization interferometric observations, the use of a new set of calibration-independent quantities (closure traces) has been proposed. However, these quantities suffer from some degeneracies, so their use in practical situations may be rather limited. In this paper, we explore the use of closure traces on simulated and real observations, showing that (with the proper selection of fitting parameters) it is possible to retrieve information on the source polarization using only closure traces and to constrain spatially resolved polarization. We carried out the first application of closure traces to the brightness modeling of real data, using the ALMA observations of M87 conducted during the April 2017 EHT campaign and quantifying a gradient in the Faraday rotation along the source structure (the M87 jet). This work opens the possibility to apply similar strategies to observations from any kind of interferometer (with a special focus on VLBI), whereby quantities such as the differential rotation measure or the spatially resolved polarization can be retrieved.

Transverse Oscillations of the M87 Jet Revealed by KaVA Observations

Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 to June 2016. The average time interval of the observation is ∼0.1 year, which is suitable for tracking short-term structural changes. From these observations, the M87 jet is well represented by double ridge lines in the region 2–12 mas from the core. We found that the ridge lines exhibit transverse oscillations in all observed regions with an average period of 0.94±0.12 years. When the sinusoidal fit is performed, we found that the amplitude of this oscillation is an order of ∼0.1 mas, and the oscillations in the northern and southern limbs are almost in phase. Considering the amplitude, it does not originate from Earth’s parallax. We propose possible scenarios of the transverse oscillation, such as the propagation of jet instabilities or magneto-hydrodynamic (MHD) waves or perturbed mass injection around magnetically dominated accretion flows.

Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities

We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to enable year-round observations. Multi-frequency imaging that incorporates 86 GHz observations would sufficiently augment the (u,v) coverage at 230 and 345 GHz to permit detection of the M87 jet structure without requiring EHT stations to join the array. The general calibration and sensitivity of the ngEHT would also be enhanced by leveraging frequency phase transfer techniques, whereby simultaneous observations at 86 GHz and higher-frequency bands have the potential to increase the effective coherence times from a few seconds to tens of minutes. When observation at the higher frequencies is not possible, there are opportunities for standalone 86 GHz science, such as studies of black hole jets and spectral lines. Finally, the addition of 86 GHz capabilities to the ngEHT would enable it to integrate into a community of other VLBI facilities—such as the GMVA and ngVLA—that are expected to operate at 86 GHz but not at the higher ngEHT observing frequencies.

Interface instabilities in hydrodynamic relativistic jets

ABSTRACT Both the dynamics and the observational properties of relativistic jets are determined by their interaction with the ambient medium. A crucial role is played by the contact discontinuity at the jet boundary, which in the presence of jet collimation may become subject to Rayleigh–Taylor instability (RTI) and Richtmyer–Meshkov instability (RMI). Here, we study the evolution of these instabilities in non-magnetized relativistic jets using special relativistic three-dimensional hydrodynamic simulations. We show that the growth of initial perturbations is consistent with relativistic RTI operating in the jet collimation region. The contribution of RMI becomes important downstream from the collimation shock in agreement with the theoretical expectations. Both instabilities reach non-linear scales above the shock convergence point and trigger strong turbulence, mixing the jet with the ambient matter. We devise an analytic solution for the mixing rate and show that it is sensitive to the external density gradients. Our results may be applied to different types of astrophysical objects. In particular, different contribution of interface instabilities is a natural explanation for the observed dichotomy between FR-I and FR-II radiogalaxies. The rapid slow-down in the jet of M87 is consistent with baryon entrainment from the circumnuclear matter with the observed density distribution. In microquasars, baryon loading triggered by interface instabilities is a probable reason for the low observed Lorentz factors. We show that the observed variability in gamma-ray bursts cannot come from mixing driven by interface instabilities and likely originates from the engine, suggesting the presence of magnetic fields in the jet.

Implications from the Velocity Profile of the M87 Jet: A Possibility of a Slowly Rotating Black Hole Magnetosphere

Motivated by the measured velocity profile of the M87 jet using the Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) by Park et al. indicating that the starting position of the jet acceleration is farther from the central engine of the jet than predicted in general relativistic magnetohydrodynamic simulations, we explore how to mitigate the apparent discrepancy between the simulations and the KaVA observation. We use a semi-analytic jet model proposed by Tomimatsu & Takahashi consistently solving the transmagnetic field structure but neglecting any dissipation effects. By comparing the jet model with the observed M87 jet velocity profile, we find that the model can reproduce the logarithmic feature of the velocity profile and can fit the observed data when choosing c/(100r g ) ≲ Ω F ≲ c/(70r g ), where r g is the gravitational radius. While a total specific energy () of the jet changes the terminal bulk Lorentz factor of the jet, a slower angular velocity of the black hole magnetosphere (Ω F ) makes a light-cylinder radius (r lc) larger, and it consequently pushes out a location of a starting point of the jet acceleration. Using the estimated Ω F we further estimate the magnetic field strength on the event horizon scale in M87 by assuming Blandford–Znajek process is in action. The corresponding magnetic flux threading the event horizon of M87 is in good agreement with a magnetically arrested disk regime.

JetCurry I. Reconstructing three-dimensional jet geometry from two-dimensional images

We present a three-dimensional (3-D) visualization of jet geometry using numerical methods based on a Markov Chain Monte Carlo (MCMC) and limited memory Broyden–Fletcher–Goldfarb–Shanno (BFGS) optimized algorithm. Our aim is to visualize the 3-D geometry of an active galactic nucleus (AGN) jet using observations, which are inherently two-dimensional (2-D) images. Many AGN jets display complex structures that include hotspots and bends. The structure of these bends in the jet’s frame may appear quite different than what we see in the sky frame, where it is transformed by our particular viewing geometry. The knowledge of the intrinsic structure will be helpful in understanding the appearance of the magnetic field and hence emission and particle acceleration processes over the length of the jet. We present the JetCurry algorithm to visualize the jet’s 3-D geometry from its 2-D image. We discuss the underlying geometrical framework and outline the method used to decompose the 2-D image. We report the results of our 3-D visualization of the jet of M87, using the test case of the knot D region. Our 3-D visualization is broadly consistent with the expected double helical magnetic field structure of knot D region of the jet. We also discuss the next steps in the development of the JetCurry algorithm.

The Details of Limb Brightening Reveal the Structure of the Base of the Jet in M87 for the First Time

It has become commonplace in astronomy to describe the transverse coarse structure of jets in loosely defined terms such as “sheath” and “spine” based on discussions of parsec scale properties. But, the applicability, dimension, and prominence of these features on sub-light-year scales has previously been unconstrained by observation. The first direct evidence of jet structure near the source in M87 is extreme limb brightening (a double-rail morphology), 0.3–0.6 mas from the source, which is prominent in observations with high resolution and sensitivity. Intensity crosscuts of these images provide three strong, interdependent constraints on the geometry responsible for the double-rail morphology: the rail to rail separation, the peak to trough intensity ratio, and the rail widths. Analyzing these constraints indicates that half or more of the jet volume resides in a thick-walled, tubular, mildly relativistic, protonic jet only ∼0.25 lt-yr (or ∼300 M, where M is the central black hole mass in geometrized units) from the source. By contrast, the Event Horizon Telescope Collaboration interprets their observations with the aid of general relativistic magnetohydrodynamic simulations that produce an invisible (by construction) jet with a surrounding luminous, thin sheath. Yet, it is shown that synthetic images of simulated jets are center brightened 0.3–0.6 mas from the source. This serious disconnection with observation occurs in a region previously claimed in the literature to be well represented by the simulations. The limb brightening analysis motivates a discussion of possible simulation modifications to improve conformance with observations.

The Average Radial Speed of Light From Near to Far Space Surrounding the Kerr–Newman Super-Gravitational Source

The Kerr–Newman metric is used to discuss the average radial speed of light from near to far space surrounding the super-gravitational source like a black hole which can be observed by a weak-gravitational reference frame such as an observer on the Earth. The velocity equation of light near the black hole is represented by the Boyer–Lindquist coordinates (t, r, θ, and ϕ), and the main parameters are the Schwarzschild radius RS, the rotation term a, and the charged term RQ. From the calculations, the average radial speed of light from r = RS to r = αRS with α>1 is possibly observed exceeding c by an observer on the Earth. The result can extend to the large r place when the rotation of the black hole is high or the charge is very large. This average radial speed finally approaches c far away from the black hole. We also propose a new explanation based on our results that the observation of the faster-than-light particle is due to the light bending near the Kerr–Newman black hole or supermassive star with very strong gravity. In addition, two superluminal theories used to explain the speed of light in astronomy are compared. One is the Doppler effect in special relativity, and the other is the change in the photon speed due to the QED contribution of one-loop vacuum polarization to the photon effective action. The former seems to mainly appear as the change of the observed wavelength or frequency, while the latter is probably the random and irregular occurrences. Our explanation is based on the Kerr–Newman metric in general relativity, and it extends the discussion from the flat spacetime in special relativity to the curved spacetime which is suitable for many superluminal observations near the super-gravitational sources like the black hole. Our calculations are used to verify tangible observations like the M87 jet.