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A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (16 November 2021) | Viewed by 31007

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Dr. Santanu Mondal

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Guest Editor

Indian Institute of Astrophysics, Bangalore 560034, India
Interests: black hole physics; accretion and accretion disk; radiative-hydrodynamics modelling; instabilities-irradiation; shocks; viscosity; cooling; turbulence on the origin of Quasi Periodic Oscillations (QPOs); X-ray data analysis; black hole mass and spin parameter estimation from spectral fitting
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Dear Colleagues,

Accretion and ejection around compact objects, mainly around black holes, both in low mass, supermassive, and intermediate-mass, is rich and has been studied exhaustively. However, the subject is expanding and growing rapidly after the launch of different space-based satellites and ground-based telescopes in multiwavelength bands, leaving a range of questions on accretion and ejection mechanisms. The proper understanding of the underlying physical mechanisms responsible for observational evidence is still lacking for several reasons. For instance, different phenomena are studied as a separate system, the hydrodynamics of one component ignores the other, spectral properties ignore timing properties or vice versa, and there is not enough instrumental resolution to decipher small scale physics.

With the advent of high-resolution satellite observations, it is possible to look at the problems globally as a complete package in a more consistent way. Recently, many new low mass black hole candidates have been discovered; however, very little is known about those systems, e.g., mass, spin parameter, orbital period. The study in the spectrotemporal domain also needs proper understanding of spectral state change, quasi periodic oscillation frequency evolution, hardness intensity diagram, and line emissions. Therefore, it is a good time to take a break, recapitulate what has been done, what is ongoing, and what can be done in the future with upcoming missions, both from a theoretical and observational perspective, bringing together experts across the electromagnetic spectrum to gain new insights into the physical process of accretion.

The goal and motivation of this collection are to focus on top-quality original works and comprehensive review papers in the abovementioned context, with important research facts that are written in a highly understandable way, from a theoretical, observational, and numerical simulation ground, where observational papers will describe measurements for testing theoretical and numerical (both hydrodynamic or magnetohydrodynamic) understandings. Copy–pastes with inconsistencies in writing will not be considered in this Collection.

This collection will give a compact and concise description of the overall view of the subject, its past, present, and future.

Dr. Santanu Mondal
Guest Editor

Galaxies 2020 Best Paper Award for Special Issue “Global Understanding of Accretion and Ejection around Black Holes” (500 CHF)

Winner announcement date: 30 September 2022
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Dear Colleagues,

To recognize the excellence of the papers in the Special Issue “Global Understanding of Accretion and Ejection around Black Holes”, we are pleased to launch our new Best Paper Award. One review or research article will receive this award. The paper will be selected after a thorough evaluation by the journal Award Committee, led by the EiC, Prof. Dr. Emilio Elizalde.

Eligibility for the award:

Authors of all career levels are eligible;
Only submissions in “Global Understanding of Accretion and Ejection around Black Holes”, excluding feature papers invited by the Guest Editor, are eligible.

Selection criteria:

The paper will be selected by the journal Award Committee according to

the following criteria (data source: Web of Science (Clarivate Analytics)):

Scientific merit and broadness of impact;
Relevance to the journal’s field;
Originality of research objectives and/or presented ideas;
Creativity of the study design or uniqueness of approaches and concepts;
Clarity of presentation;
Citation and download rates by 30 June 2022;
Authorship (first author, teamwork, and collaboration with other institutions).

Prizes:

The winner will receive the following:

A certificate;
500 CHF;
A waiver to publish a feature paper in Galaxies (following the standard peer review procedure, within one year after the award is announced).

The winner will be announced on the journal website in September 2022.

Please submit your paper here (https://susy.mdpi.com/user/manuscripts/upload?form[journal_id]=53&form[special_issue_id]=58205), the sooner the better.

Kind regards,

Galaxies Editorial Office

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

black holes
X-ray binaries
accretion
accretion disks
jets
quasi-periodic oscillations hydrodynamics
LMBHBs
AGNs
ULXs
hydrodynamics
MHD
shocks
viscosity
radiative transfer
line emission
X-ray instrumentation

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Published Papers (11 papers)

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Editorial

Jump to: Research

3 pages, 199 KiB

Open AccessEditorial

Global Understanding of Accretion and Ejection around Black Holes

by Santanu Mondal

Galaxies 2022, 10(3), 64; https://doi.org/10.3390/galaxies10030064 - 27 Apr 2022

Viewed by 1975

Abstract

Accretion and ejection around compact objects, mainly around black holes, both in low mass, and supermassive, is rich and has been studied exhaustively [...] Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

Research

Jump to: Editorial

17 pages, 584 KiB

Open AccessArticle

Isolating an Outflow Component in Single-Epoch Spectra of Quasars

by Paola Marziani, Alice Deconto-Machado and Ascension Del Olmo

Galaxies 2022, 10(2), 54; https://doi.org/10.3390/galaxies10020054 - 24 Mar 2022

Cited by 7 | Viewed by 2575

Abstract

Gaseous outflows appear to be a universal property of type-1 and type-2 active galactic nuclei (AGN). The main diagnostic is provided by emission features shifted to higher frequencies via the Doppler effect, implying that the emitting gas is moving toward the observer. However, beyond the presence of blueshift, the observational signatures of the outflows are often unclear, and no established criteria exist to isolate the outflow contribution in the integrated, single-epoch spectra of type-1 AGN. The emission spectrum collected the typical apertures of long-slit spectroscopy or of fiber optics sample contributions over a broad range of spatial scales, making it difficult to analyze the line profiles in terms of different kinematical components. Nevertheless, hundred of thousands of quasars spectra collected at moderate resolution demand a proper analysis of the line profiles for proper dynamical modeling of the emitting regions. In this small contribution, we analyze several profiles of the Hi Balmer line H

β

from composite and individual spectra of sources radiating at moderate Eddington ratio (Population B). Features and profile shapes that might be traced to outflow due to narrow-line region gas are detected over a wide range of luminosity. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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14 pages, 584 KiB

Open AccessArticle

Non-Thermal Emission from Radio-Loud AGN Jets: Radio vs. X-rays

by Elena Fedorova, Bohdan Hnatyk, Antonino Del Popolo, Anatoliy Vasylenko and Vadym Voitsekhovskyi

Galaxies 2022, 10(1), 6; https://doi.org/10.3390/galaxies10010006 - 4 Jan 2022

Cited by 7 | Viewed by 2788

Abstract

We consider the sample of 55 blazars and Seyferts cross-correlated from the Planck all-sky survey based on the Early Release Compact Source Catalog (ERCSC) and Swift BAT 105-Month Hard X-ray Survey. The radio Planck spectra vs. X-ray Swift/XRT+BAT spectra of the active galactic nuclei (AGN) sample were fitted with the simple and broken power law (for the X-ray spectra taking into account also the Galactic neutral absorption) to test the dependencies between the photon indices of synchrotron emission (in radio range) and synchrotron self-Compton (SSC) or inverse-Compton emission (in X-rays). We show that for the major part of the AGN in our sample there is a correspondence between synchrotron and SSC photon indices (one of two for broken power-law model) compatible within the error levels. For such objects, this can give a good perspective for the task of distinguishing between the jet base counterpart from that one emitted in the disk+corona AGN “central engine”. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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28 pages, 939 KiB

Open AccessFeature PaperArticle

Promise of Persistent Multi-Messenger Astronomy with the Blazar OJ 287

by Mauri J. Valtonen, Lankeswar Dey, Achamveedu Gopakumar, Staszek Zola, S. Komossa, Tapio Pursimo, Jose L. Gomez, Rene Hudec, Helen Jermak and Andrei V. Berdyugin

Galaxies 2022, 10(1), 1; https://doi.org/10.3390/galaxies10010001 - 22 Dec 2021

Cited by 25 | Viewed by 3800

Abstract

Successful observations of the seven predicted bremsstrahlung flares from the unique bright blazar OJ 287 firmly point to the presence of a nanohertz gravitational wave (GW) emitting supermassive black hole (SMBH) binary central engine. We present arguments for the continued monitoring of the source in several electromagnetic windows to firmly establish various details of the SMBH binary central engine description for OJ 287. In this article, we explore what more can be known about this system, particularly with regard to accretion and outflows from its two accretion disks. We mainly concentrate on the expected impact of the secondary black hole on the disk of the primary on 3 December 2021 and the resulting electromagnetic signals in the following years. We also predict the times of exceptional fades, and outline their usefulness in the study of the host galaxy. A spectral survey has been carried out, and spectral lines from the secondary were searched for but were not found. The jet of the secondary has been studied and proposals to discover it in future VLBI observations are mentioned. In conclusion, the binary black hole model explains a large number of observations of different kinds in OJ 287. Carefully timed future observations will be able to provide further details of its central engine. Such multi-wavelength and multidisciplinary efforts will be required to pursue multi-messenger nanohertz GW astronomy with OJ 287 in the coming decades. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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10 pages, 408 KiB

Open AccessArticle

γ-ray Flux and Spectral Variability of Blazar Ton 599 during Its 2021 Flare

by Bhoomika Rajput and Ashwani Pandey

Galaxies 2021, 9(4), 118; https://doi.org/10.3390/galaxies9040118 - 13 Dec 2021

Cited by 4 | Viewed by 2318

Abstract

Blazars are known to emit exceptionally variable non-thermal emission over the wide range (from radio to

γ

-rays) of electromagnetic spectrum. We present here the results of our

γ

-ray flux and spectral variability study of the blazar Ton 599, which has been [...] Read more.

Blazars are known to emit exceptionally variable non-thermal emission over the wide range (from radio to

γ

-rays) of electromagnetic spectrum. We present here the results of our

γ

-ray flux and spectral variability study of the blazar Ton 599, which has been recently observed in the

γ

-ray flaring state. Using 0.1–300 GeV

γ

-ray data from the

Fermi

Gamma-ray Space Telescope (hereinafter

Fermi

), we generated one-day binned light curve of Ton 599 for a period of about one-year from MJD 59,093 to MJD 59,457. During this one year period, the maximum

γ

-ray flux detected was 2.24 ± 0.25 ×

10^{- 6}

ph cm

^{- 2}

^{- 1}

at MJD 59,399.50. We identified three different flux states, namely, epoch A (quiescent), epoch B (pre-flare) and epoch C (main-flare). For each epoch, we calculated the

γ

-ray flux variability amplitude (F

_{v a r}

) and found that the source showed largest flux variations in epoch C with F

_{v a r} \sim

35%. We modelled the

γ

-ray spectra for each epoch and found that the Log-parabola model adequately describes the

γ

-ray spectra for all the three epochs. We estimated the size of the

γ

-ray emitting region as 1.03 ×

10^{16}

cm and determined that the origin of

γ

-ray radiation, during the main-flare, could be outside of the broad line region. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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16 pages, 1832 KiB

Open AccessArticle

The Radiative Newtonian 1 < γ ≤ 1.66 and the Paczyński–Wiita γ = 5/3 Regime of Non-Isothermal Bondi Accretion onto a Massive Black Hole with an Accretion Disc

by Jose M. Ramírez-Velásquez, Leonardo Di G. Sigalotti, Ruslan Gabbasov, Jaime Klapp and Ernesto Contreras

Galaxies 2021, 9(3), 55; https://doi.org/10.3390/galaxies9030055 - 11 Aug 2021

Cited by 1 | Viewed by 2276

Abstract

We investigate the non-isothermal Bondi accretion onto a supermassive black hole (SMBH) for the unexplored case when the adiabatic index is varied in the interval

1 < γ \leq 1.66

and for the Paczyński–Wiita

γ = 5 / 3

regime, including the effects [...] Read more.

We investigate the non-isothermal Bondi accretion onto a supermassive black hole (SMBH) for the unexplored case when the adiabatic index is varied in the interval

1 < γ \leq 1.66

and for the Paczyński–Wiita

γ = 5 / 3

regime, including the effects of X-ray heating and radiation force due to electron scattering and spectral lines. The X-ray/central object radiation is assumed to be isotropic, while the UV emission from the accretion disc is assumed to have an angular dependence. This allows us to build streamlines in any desired angular direction. The effects of both types of radiation on the accretion dynamics is evaluated with and without the effects of spectral line driving. Under line driving (and for the studied angles), when the UV flux dominates over the X-ray heating, with a fraction of UV photons going from 80% to 95%, and

γ

varies from

1.66

1.1

, the inflow close to the gravitational source becomes more supersonic and the volume occupied by the supersonic inflow becomes larger. This property is also seen when this fraction goes from 50% to 80%. The underestimation of the Bondi radius close to the centre increases with increasing

γ

, while the central overestimation of the accretion rates decreases with increasing

γ

, for all the six studied cases. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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8 pages, 255 KiB

Open AccessArticle

Geodesic Circular Orbits Sharing the Same Orbital Frequencies in the Black String Spacetime

by Sanjar Shaymatov and Farruh Atamurotov

Galaxies 2021, 9(2), 40; https://doi.org/10.3390/galaxies9020040 - 28 May 2021

Cited by 17 | Viewed by 2552

Abstract

We consider isofrequency pairing of geodesic orbits that share the same three orbital frequencies associated with

Ω^{\hat{r}}

Ω^{\hat{φ}}

, and

Ω^{\hat{ω}}

in a particular region of parameter space around black string spacetime geometry. We study the [...] Read more.

We consider isofrequency pairing of geodesic orbits that share the same three orbital frequencies associated with

Ω^{\hat{r}}

Ω^{\hat{φ}}

, and

Ω^{\hat{ω}}

in a particular region of parameter space around black string spacetime geometry. We study the effect of a compact extra spatial dimension on the isofrequency pairing of geodesic orbits and show that such orbits would occur in the allowed region when particles move along the black string. We find that the presence of the compact extra dimension leads to an increase in the number of the isofrequency pairing of geodesic orbits. Interestingly we also find that isofrequency pairing of geodesic orbits in the region of parameter space cannot be realized beyond the critical value

J_{c r} \approx 0.096

of the conserved quantity of the motion arising from the compact extra spatial dimension. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

21 pages, 657 KiB

Open AccessArticle

Study of Accretion Flow Dynamics of V404 Cygni during Its 2015 Outburst

by Arghajit Jana, Jie-Rou Shang, Dipak Debnath, Sandip K. Chakrabarti, Debjit Chatterjee and Hsiang-Kuang Chang

Galaxies 2021, 9(2), 39; https://doi.org/10.3390/galaxies9020039 - 25 May 2021

Cited by 3 | Viewed by 2926

Abstract

The 2015 Outburst of V404 Cygni is an unusual one with several X-ray and radio flares and rapid variation in the spectral and timing properties. The outburst occurred after 26 years of inactivity of the black hole. We study the accretion flow properties of the source during its initial phase of the outburst using Swift/XRT and Swift/BAT data in the energy range of 0.5–150 keV. We have done spectral analysis with the two component advective flow (TCAF) model fits file. Several flow parameters such as two types of accretion rates (Keplerian disk and sub-Keplerian halo), shock parameters (location and compression ratio) are extracted to understand the accretion flow dynamics. We calculated equipartition magnetic field

B_{e q}

for the outburst and found that the highest

B_{e q} \sim 900

Gauss. Power density spectra (PDS) showed no break, which indicates no or very less contribution of the Keplerian disk component, which is also seen from the result of the spectral analysis. No signature of prominent quasi-periodic oscillations (QPOs) is observed in the PDS. This is due to the non-satisfaction of the condition for the resonance shock oscillation as we observed mismatch between the cooling timescale and infall timescale of the post-shock matter. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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10 pages, 812 KiB

Open AccessArticle

Properties of Faint X-ray Activity of XTE J1908+094 in 2019

by Debjit Chatterjee, Arghajit Jana, Kaushik Chatterjee, Riya Bhowmick, Sujoy Kumar Nath, Sandip K. Chakrabarti, A. Mangalam and Dipak Debnath

Galaxies 2021, 9(2), 25; https://doi.org/10.3390/galaxies9020025 - 16 Apr 2021

Cited by 6 | Viewed by 2190

Abstract

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe K

α

emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be

6 . 5_{- 0.7}^{+ 0.5} M_{⊙}

, with 90% confidence. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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14 pages, 1386 KiB

Open AccessArticle

Changing Accretion Geometry of Seyfert 1 Mrk 335 with NuSTAR: A Comparative Study

by Santanu Mondal and C. S. Stalin

Galaxies 2021, 9(2), 21; https://doi.org/10.3390/galaxies9020021 - 25 Mar 2021

Cited by 7 | Viewed by 2600

Abstract

We present a detailed spectral study of the narrow-line Seyfert 1 galaxy, Markarian 335, using eight epoch observations made between 2013 and 2020 with the Nuclear Spectroscopic Telescope Array. The source was variable during this period both in spectral flux and flow geometry. We estimated the height of the Compton cloud from the model fitted parameters for the whole observation period. This allowed us to investigate the underlying physical processes that drive the variability in X-rays. Our model fitted mass varies in a narrow range, between

(2.44 \pm 0.45 - 3.04 \pm 0.56) \times 10^{7} M_{⊙}

, however, given the large error bars, it is consistent with being constant and is in agreement with that known from optical reverberation mapping observations. The disk mass accretion rate reached a maximum of 10% of the Eddington rate during June 2013. Our study sheds light on mass outflows from the system and also compares different aspects of accretion with X-ray binaries. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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9 pages, 261 KiB

Open AccessEditor’s ChoiceArticle

Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics

by Chandra B. Singh, David Garofalo and Benjamin Lang

Galaxies 2021, 9(1), 10; https://doi.org/10.3390/galaxies9010010 - 26 Jan 2021

Cited by 2 | Viewed by 2998

Abstract

The discovery of 3C 273 in 1963, and the emergence of the Kerr solution shortly thereafter, precipitated the current era in astrophysics focused on using black holes to explain active galactic nuclei (AGN). But while partial success was achieved in separately explaining the bright nuclei of some AGN via thin disks, as well as powerful jets with thick disks, the combination of both powerful jets in an AGN with a bright nucleus, such as in 3C 273, remained elusive. Although numerical simulations have taken center stage in the last 25 years, they have struggled to produce the conditions that explain them. This is because radiatively efficient disks have proved a challenge to simulate. Radio quasars have thus been the least understood objects in high energy astrophysics. But recent simulations have begun to change this. We explore this milestone in light of scale-invariance and show that transitory jets, possibly related to the jets seen in these recent simulations, as some have proposed, cannot explain radio quasars. We then provide a road map for a resolution. Full article

(This article belongs to the Special Issue Global Understanding of Accretion and Ejection around Black Holes)

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