Galaxies

11 pages, 3280 KiB

Open AccessReview

by Francoise Combes

Galaxies 2023, 11(6), 120; https://doi.org/10.3390/galaxies11060120 - 13 Dec 2023

Cited by 1 | Viewed by 1164

Since the 1970s, astronomers have struggled with the issue of how matter can be accreted to promote black-hole growth. While low-angular-momentum stars may be devoured by a black hole, they are not a sustainable source of fuel. Gas, which could potentially provide an [...] Read more.

Since the 1970s, astronomers have struggled with the issue of how matter can be accreted to promote black-hole growth. While low-angular-momentum stars may be devoured by a black hole, they are not a sustainable source of fuel. Gas, which could potentially provide an abundant fuel source, presents another challenge due to its enormous angular momentum. While viscous torques are not significant, gas is subject to gravity torques from non-axisymmetric potentials such as bars and spirals. Primary bars can exchange angular momentum with the gas within corotation, causing it to spiral inwards until reaching the inner Lindblad resonance. An embedded nuclear bar can then take over. As the gas reaches the black hole’s sphere of influence, the torque becomes negative, fueling the center. Dynamical friction also accelerates the infall of gas clouds closer to the nucleus. However, because of the Eddington limit, growing a black hole from a stellar-mass seed is a slow process. The existence of very massive black holes in the early universe remains a puzzle that could potentially be solved through direct collapse of massive clouds into black holes or super-Eddington accretion. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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20 pages, 8333 KiB

Open AccessArticle

S0 Galaxies: Outer Gas Accretion through Tidal Interaction and Minor Merging

by Olga Sil’chenko, Alexei V. Moiseev, Alexandrina Smirnova and Roman Uklein

Galaxies 2023, 11(6), 119; https://doi.org/10.3390/galaxies11060119 - 08 Dec 2023

Viewed by 1332

Abstract

To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the H

α

emission line by using the scanning Fabry–Perot interferometer of the 6m telescope of the Special Astrophysical Observatory RAS. We [...] Read more.

To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the H

α

emission line by using the scanning Fabry–Perot interferometer of the 6m telescope of the Special Astrophysical Observatory RAS. We find perspective accretion flows seen as ionized-gas emission filaments between the galaxies. We discuss the whole kinematics and origin of these flows. Full article

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19 pages, 6571 KiB

Open AccessReview

Ionizing Spotlight of Active Galactic Nucleus

by Alexei V. Moiseev and Aleksandrina A. Smirnova

Galaxies 2023, 11(6), 118; https://doi.org/10.3390/galaxies11060118 - 07 Dec 2023

Cited by 1 | Viewed by 2170

Abstract

Ionization cones and relativistic jets give us one of the most large-scale example of active galactic nuclei (AGN) influence on the surrounding gas environment in galaxies and beyond. The study of ionization cones makes it possible not only to test the predictions of [...] Read more.

Ionization cones and relativistic jets give us one of the most large-scale example of active galactic nuclei (AGN) influence on the surrounding gas environment in galaxies and beyond. The study of ionization cones makes it possible not only to test the predictions of the unified model of galactic activity, but also to probe galaxy gas environment and trace how the luminosity of the nucleus changes over time (a light echo). In the external galactic or even extragalactic gas ionization cones create Extended Emission-Line Regions (EELRs) which can span distances from several to hundreds kpc away a host galaxy. We review the recent results of studying the gas kinematics and its ionization properties in EELRs with a special attention to search of fading AGN radiation on the time scale

few \times (10^{4} - 10^{5})

years.The role of modern narrow-band and integral-field surveys in these researches is also considered. Full article

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24 pages, 603 KiB

Open AccessArticle

Testing a Lepto-Hadronic Two-Zone Model with Extreme High-Synchrotron Peaked BL Lacs and Track-like High-Energy Neutrinos

by Edilberto Aguilar-Ruiz, Antonio Galván-Gámez and Nissim Fraija

Galaxies 2023, 11(6), 117; https://doi.org/10.3390/galaxies11060117 - 06 Dec 2023

Viewed by 1141

Abstract

Numerous studies suggest that high-energy (HE) neutrinos and ultra-high-energy (UHE) cosmic rays could originate from extremely high-synchrotron peaked (EHSP) BL Lacs, which have been identified as effective particle accelerators. Due to the discovery of HE-neutrinos by the IceCube telescope, these hypotheses may shortly [...] Read more.

Numerous studies suggest that high-energy (HE) neutrinos and ultra-high-energy (UHE) cosmic rays could originate from extremely high-synchrotron peaked (EHSP) BL Lacs, which have been identified as effective particle accelerators. Due to the discovery of HE-neutrinos by the IceCube telescope, these hypotheses may shortly have the opportunity to be tested. In this work, we use a two-zone leptohadronic model to explain the spatial coincidence of three EHSP BL Lac: 1RXS J09462.5+010459, 1ES 1101-232, and 3HSP J095507.9+355101 with the arrival of track-like neutrinos. Our results for 1RXS J09462.5+010459 and 1ES 1101-232 indicate that the model accurately describes the electromagnetic emission and neutrino events without increasing the fluxes in the measured bands. In addition, the X-ray flaring state of 3HSP J095507.9+355101 can be explained by our model, but the measured ultraviolet flux during the neutrino arrival time window cannot be explained. For all cases, the broadband emission and neutrino arrival are better described by hard proton distributions ≈1.5. Finally, the proton luminosity required to explain the neutrino fluxes is slightly higher than the Eddington limit with a photopion efficiency of ≈0.1 for non-flaring state cases. On the other hand, for the flaring state of 3HSP J095507.9+355101, the proton luminosity must be higher than the Eddington limit at least by one order of magnitude, even if the photopion efficiency reaches unity. Full article

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8 pages, 310 KiB

Open AccessCommunication

On the Maximum Energy Release from Formation of Static Compact Objects

by Abhas Mitra and Krishna Kumar Singh

Galaxies 2023, 11(6), 116; https://doi.org/10.3390/galaxies11060116 - 21 Nov 2023

Viewed by 1512

Abstract

Type II Supernova 1987A (SN 1987A), observed in 1987, released an energy of

Q \approx 3 \times 10^{53}

erg. This huge energy is essentially the magnitude of gravitational potential or self-gravitational energy (PE) of a new born cold neutron star having a [...] Read more.

Type II Supernova 1987A (SN 1987A), observed in 1987, released an energy of

Q \approx 3 \times 10^{53}

erg. This huge energy is essentially the magnitude of gravitational potential or self-gravitational energy (PE) of a new born cold neutron star having a gravitational compactness or redshift

z_{b} \approx 0.15

. One may wonder what could be the upper limit on the amount of energy that might be released with the formation of a cold Ultra Compact Object (UCO) with an arbitrary high

z_{b}

. Accordingly, here, for the first time, we obtain an analytical expression for the PE of a homogeneous general relativistic UCO assuming it to be cold and static. It is found that the PE of a homogeneous UCO of mass M may exceed Mc² and be as large as 1.34 Mc². This result, though surprising, follows from an exact and correct analytical calculation based on the standard General Theory of Relativity (GTR). Further, UCOs supported by tangential stresses may be inhomogeneous and much more massive than neutron stars with PE ∼ 2.1 Mc² Thus, in principle, formation of an UCO of a few solar masses (

M_{⊙}

) might release an energy

Q \sim 10^{55}

erg. Full article

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11 pages, 1240 KiB

Open AccessArticle

Holographic Quantum-Foam Blurring Is Consistent with Observations of Gamma-Ray Burst GRB221009A

by Eric Steinbring

Galaxies 2023, 11(6), 115; https://doi.org/10.3390/galaxies11060115 - 17 Nov 2023

Cited by 1 | Viewed by 1547

Abstract

Gamma-ray burst GRB221009A was of unprecedented brightness in the

γ

-rays and X-rays through to the far ultraviolet, allowing for identification within a host galaxy at redshift

z = 0.151

by multiple space and ground-based optical/near-infrared telescopes and enabling a first association—via cosmic-ray [...] Read more.

Gamma-ray burst GRB221009A was of unprecedented brightness in the

γ

-rays and X-rays through to the far ultraviolet, allowing for identification within a host galaxy at redshift

z = 0.151

by multiple space and ground-based optical/near-infrared telescopes and enabling a first association—via cosmic-ray air-shower events—with a photon of 251 TeV. That is in direct tension with a potentially observable phenomenon of quantum gravity (QG), where spacetime “foaminess” accumulates in wavefronts propagating cosmological distances, and at high-enough energy could render distant yet bright pointlike objects invisible, by effectively spreading their photons out over the whole sky. But this effect would not result in photon loss, so it remains distinct from any absorption by extragalactic background light. A simple multiwavelength average of foam-induced blurring is described, analogous to atmospheric seeing from the ground. When scaled within the fields of view for the Fermi and Swift instruments, it fits all

z \leq 5

GRB angular-resolution data of 10 MeV or any lesser peak energy and can still be consistent with the highest-energy localization of GRB221009A: a limiting bound of about 1 degree is in agreement with a holographic QG-favored formulation. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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22 pages, 10637 KiB

Open AccessArticle

A Study of the Properties and Dynamics of the Disk of Satellites in a Milky-Way-like Galaxy System

by Xinghai Zhao, Grant J. Mathews, Lara Arielle Phillips and Guobao Tang

Galaxies 2023, 11(6), 114; https://doi.org/10.3390/galaxies11060114 - 16 Nov 2023

Cited by 1 | Viewed by 1164

Abstract

The dynamics of the satellite systems of Milky-Way-like galaxies offer a useful means by which to study the galaxy formation process in the cosmological context. It has been suggested that the currently observed anisotropic distribution of the satellites in such galaxy systems is [...] Read more.

The dynamics of the satellite systems of Milky-Way-like galaxies offer a useful means by which to study the galaxy formation process in the cosmological context. It has been suggested that the currently observed anisotropic distribution of the satellites in such galaxy systems is inconsistent with the concordance

Λ C D M

cosmology model on the galactic scale if the observed satellites are random samples of the dark matter (DM) sub-halos that are nearly isotropically distributed around the central galaxy. In this study, we present original high-resolution zoom-in studies of central galaxies and satellite systems based upon initial conditions for the DM distribution from the Aquarius simulations but with substantial high-resolution baryon physics added. We find that the galaxy most like the Milky Way in this study does indeed contain a disk of satellites (DOS). Although one galaxy DOS system does not answer the question of how common such disks are, it does allow the opportunity to explore the properties and dynamics of the DOS system. Our investigation centers on the spatial arrangement (distances, angles, etc.) of satellites in this Milky-Way-like galaxy system with a specific emphasis on identifying and analyzing the disk-like structure along with its dynamical and morphological properties. Among the conclusions from this study, we find that the satellites and DM sub-halos in the galaxy simulations are anisotropically distributed. The dynamical properties of the satellites, however, indicate that the direction of the angular momentum vector of the whole satellite system is different from the normal direction of the fitted DOS and from the normal direction of the velocity dispersion of the system. Hence, the fitted DOS appears to be comprised of infalling sub-halos and is not a rotationally supported system. Full article

(This article belongs to the Special Issue Galactic Structure and Dynamics)

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13 pages, 1191 KiB

Open AccessArticle

Quasiperiodic Oscillations and Dynamics of Test Particles around Regular-Kiselev Black Holes

by Javlon Rayimbaev, Nozima Juraeva, Malika Khudoyberdiyeva, Ahmadjon Abdujabbarov and Mardon Abdullaev

Galaxies 2023, 11(6), 113; https://doi.org/10.3390/galaxies11060113 - 16 Nov 2023

Cited by 2 | Viewed by 1057

Abstract

Testing gravity theories combining (massive and massless) scalar & electrodynamic fields become the most important issue in relativistic astrophysics using data from, black hole observations. In the present work, we first show a spherically symmetric black hole solution in general relativity coupling to [...] Read more.

Testing gravity theories combining (massive and massless) scalar & electrodynamic fields become the most important issue in relativistic astrophysics using data from, black hole observations. In the present work, we first show a spherically symmetric black hole solution in general relativity coupling to generic-type nonlinear electrodynamics (NED) together with the quintessential field. We also obtain possible values for the parameters of the quintessential field and NED charge in the black hole environment for different values of degree of nonlinearity. Also, event horizon properties and scalar invariants of the black hole spacetime are studied. We investigate the equatorial motion of test particles around the regular-Kiselev black holes and study the combined effects of quintessential field and the NED charge of the black hole on particle angular momentum together with its energy at their circular orbits as well as their innermost circular stable orbits (ISCOs) and compared the obtained results with Reissner-Nordström black hole (RN BH) case. Moreover, we study particle oscillations along the orbits above than ISCO and applications to quasiperiodic oscillations (QPOs) where we obtain constrain values for the quintessential parameter and black hole mass charge parameters using observational QPO data from microquasars. Full article

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19 pages, 1320 KiB

Open AccessArticle

Exoplanets around Red Giants: Distribution and Habitability

by Ruixuan E. Chen, Jonathan H. Jiang, Philip E. Rosen, Kristen A. Fahy and Yanbei Chen

Galaxies 2023, 11(6), 112; https://doi.org/10.3390/galaxies11060112 - 16 Nov 2023

Viewed by 1547

Abstract

As the search for exoplanets continues, more are being discovered orbiting Red Giant stars. We use current data from the NASA Exoplanet Archive to investigate planet distribution around Red Giant stars and their presence in the host’s habitable zone. As well, we explore [...] Read more.

As the search for exoplanets continues, more are being discovered orbiting Red Giant stars. We use current data from the NASA Exoplanet Archive to investigate planet distribution around Red Giant stars and their presence in the host’s habitable zone. As well, we explore the distribution of planet mass and orbital semi major axis for evolved stars with increasing stellar radii. From the distance distribution of the planets, we found evidence of engulfment during the post-Main Sequence evolution of the star. We found 9 Red Giant-hosted exoplanets, and 21 Subgiant-hosted exoplanets to be in the optimistically calculated habitable zone, 5 and 17 of which are in a more conservatively calculated habitable zone. All the planets detected within their habitable zone orbit stars that are in early stages of evolution. We believe that with more powerful instrumentation, more habitable planets may be found around stars that are in later stages of evolution. Full article

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13 pages, 1673 KiB

Open AccessArticle

Optimization of Quantum Noise in Space Gravitational-Wave Antenna DECIGO with Optical-Spring Quantum Locking Considering Mixture of Vacuum Fluctuations in Homodyne Detection

by Kenji Tsuji, Tomohiro Ishikawa, Kentaro Komori, Koji Nagano, Yutaro Enomoto, Yuta Michimura, Kurumi Umemura, Ryuma Shimizu, Bin Wu, Shoki Iwaguchi, Yuki Kawasaki, Akira Furusawa and Seiji Kawamura

Galaxies 2023, 11(6), 111; https://doi.org/10.3390/galaxies11060111 - 09 Nov 2023

Cited by 1 | Viewed by 1149

Abstract

Quantum locking using optical spring and homodyne detection has been devised to reduce the quantum noise that limits the sensitivity of the DECIGO, a space-based gravitational-wave antenna in the frequency band around 0.1 Hz for the detection of primordial gravitational waves. The reduction [...] Read more.

Quantum locking using optical spring and homodyne detection has been devised to reduce the quantum noise that limits the sensitivity of the DECIGO, a space-based gravitational-wave antenna in the frequency band around 0.1 Hz for the detection of primordial gravitational waves. The reduction in the upper limit of energy density

Ω_{GW}

from

2 \times 10^{- 15}

to

1 \times 10^{- 16}

, as inferred from recent observations, necessitates improved sensitivity in the DECIGO to meet its primary science goals. To accurately evaluate the effectiveness of this method, this paper considers a detection mechanism that takes into account the influence of vacuum fluctuations on homodyne detection. In addition, an advanced signal processing method is devised to efficiently utilize signals from each photodetector, and design parameters for this configuration are optimized for the quantum noise. Our results show that this method is effective in reducing quantum noise, despite the detrimental impact of vacuum fluctuations on its sensitivity. Full article

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43 pages, 12994 KiB

Open AccessArticle

Simulated Radio and Neutrino Imaging of a Microquasar

by Theodoros Smponias

Galaxies 2023, 11(6), 110; https://doi.org/10.3390/galaxies11060110 - 09 Nov 2023

Viewed by 1014

Abstract

Microquasar stellar systems emit electromagnetic radiation and high-energy particles. Thanks to their location within our own galaxy, they can be observed in high detail. Still, many of their inner workings remain elusive; hence, simulations, as the link between observations and theory, are highly [...] Read more.

Microquasar stellar systems emit electromagnetic radiation and high-energy particles. Thanks to their location within our own galaxy, they can be observed in high detail. Still, many of their inner workings remain elusive; hence, simulations, as the link between observations and theory, are highly useful. In this paper, both high-energy particle and synchrotron radio emissions from simulated microquasar jets are calculated using special relativistic imaging. A finite ray speed imaging algorithm is employed on hydrodynamic simulation data, producing synthetic images seen from a stationary observer. A hydrodynamical model is integrated in the above emission models. Synthetic spectra and maps are then produced that can be compared to observations from detector arrays. As an application, the model synthetically observes microquasars during an episodic ejection at two different spatio-temporal scales: one on the neutrino emission region scale and the other on the synchrotron radio emission scale. The results are compared to the sensitivity of existing detectors. Full article

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11 pages, 1252 KiB

Open AccessCommunication

On the Possible Asymmetry in Gamma Rays from Andromeda Due to Inverse Compton Scattering of Star Light on Electrons from Dark Matter Annihilation

by Konstantin Belotsky and Maxim Solovyov

Galaxies 2023, 11(6), 109; https://doi.org/10.3390/galaxies11060109 - 07 Nov 2023

Viewed by 967

Abstract

Dark matter is a popular candidate to a new source of primary-charged particles, especially positrons in cosmic rays, which are proposed to account for observable anomalies. While this hypothesis of decaying or annihilating DM is mostly applied for our Galaxy, it could possibly [...] Read more.

Dark matter is a popular candidate to a new source of primary-charged particles, especially positrons in cosmic rays, which are proposed to account for observable anomalies. While this hypothesis of decaying or annihilating DM is mostly applied for our Galaxy, it could possibly lead to some interesting phenomena when applied for the other ones. In this work, we look into the hypothetical asymmetry in gamma radiation from the upper and lower hemisphere of the dark matter halo of the Andromeda galaxy due to inverse Compton scattering of starlight on the DM-produced electrons and positrons. While our 2D toy model raises expectations for the possible effect, a more complex approach gives negligible effect for the dark halo case, but shows some prospects for a dark disk model. Full article

(This article belongs to the Special Issue Galactic Structure and Dynamics)

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12 pages, 6216 KiB

Open AccessCommunication

The Structure of Micro-Variability in the WEBT BL Lacertae Observation

by James R. Webb and Ivan Parra Sanz

Galaxies 2023, 11(6), 108; https://doi.org/10.3390/galaxies11060108 - 01 Nov 2023

Viewed by 1163

Abstract

We present the results of an in-depth analysis of the Whole Earth Blazar Telescope (WEBT) micro-variability observations made during a campaign done in 2020 on the blazar BL Lacertae. The data consisted of 231 days of optical imaging and we separated the long-term [...] Read more.

We present the results of an in-depth analysis of the Whole Earth Blazar Telescope (WEBT) micro-variability observations made during a campaign done in 2020 on the blazar BL Lacertae. The data consisted of 231 days of optical imaging and we separated the long-term light curve into individual single-night light curves, and then chose 41 nights that contained over 100 individual observations and also showed micro-variations well above the noise. Micro-variability is defined as excursions in the order of 0.01–0.1 magnitudes over timescales of hours or minutes either above or below a linear background sampled over the entire night. We then fit each individual micro-variability curve with model pulses from turbulent cells using the turbulent jet model.. We present the results of the pulse fitting analysis, which yields turbulent cell sizes, amplitudes and turbulent plasma characteristics. Full article

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Galaxies, Volume 11, Issue 6 (December 2023) – 13 articles

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