Journal Description
Galaxies
Galaxies
is an international, peer-reviewed, open access journal on astronomy, astrophysics, and cosmology published bimonthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Astrophysics Data System, INSPIRE, Inspec, and other databases.
- Journal Rank: CiteScore - Q2 (Astronomy and Astrophysics)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 21 days after submission; acceptance to publication is undertaken in 4.9 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
2.5 (2022);
5-Year Impact Factor:
1.9 (2022)
Latest Articles
The Revised Third Cambridge Catalogue at 60: To Jet or Not to Jet …
Galaxies 2024, 12(1), 3; https://doi.org/10.3390/galaxies12010003 - 11 Jan 2024
Abstract
The Revised Third Cambridge Catalogue of Radio Sources (in the northern sky), or 3CR, published sixty years ago by Bennett (1962) [...]
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(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)
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A Lepton–Hadron Model for the Multi-Wavelength Emission from Extreme High-Frequency Peaked BL Lacertae 1ES 1218+304
Galaxies 2024, 12(1), 2; https://doi.org/10.3390/galaxies12010002 - 29 Dec 2023
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We develop a lepton–hadron model for the possible origin of hard very high energy (VHE) spectra from a distant blazar. The model includes synchrotron self-Compton (SSC) and hadronic components. The lepton components include synchrotron radiation and inverse Compton scattering of relativistic electrons. For
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We develop a lepton–hadron model for the possible origin of hard very high energy (VHE) spectra from a distant blazar. The model includes synchrotron self-Compton (SSC) and hadronic components. The lepton components include synchrotron radiation and inverse Compton scattering of relativistic electrons. For the hadronic components, we consider proton synchrotron radiation and investigate the interaction of protons with the synchrotron emission soft photons or cosmic microwave background (CMB) photons. Upon adopting the parametrization of the observed spectrum of 1ES 1218+304, we obtain the following results: (1) the model is able to match the spectral energy distribution of 1ES 1218+304; (2) we find that in , the -ray process contributes the majority of the secondary photons; and (3) the interaction of protons with the low-energy photons may occur in or outside the jet.
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Formation of Transitional cE/UCD Galaxies through Massive/Dwarf Disc Galaxy Mergers
Galaxies 2024, 12(1), 1; https://doi.org/10.3390/galaxies12010001 - 25 Dec 2023
Abstract
The dynamics of the merger of a dwarf disc galaxy with a massive spiral galaxy of the Milky Way type were studied in detail. The remnant of such interaction after numerous crossings of the satellite through the disc of the main galaxy was
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The dynamics of the merger of a dwarf disc galaxy with a massive spiral galaxy of the Milky Way type were studied in detail. The remnant of such interaction after numerous crossings of the satellite through the disc of the main galaxy was a compact stellar core, the characteristics of which were close to small compact elliptical galaxies (cEs) or large ultra-compact dwarfs (UCDs). Such transitional cE/UCD objects with an effective radius of 100–200 pc arise as a result of stripping the outer layers of the stellar core during the destruction of a dwarf disc galaxy. Numerical models of the satellite before interaction included baryonic matter (stars and gas) and dark mass. We used N-body to describe the dynamics of stars and dark matter, and we used smoothed-particle hydrodynamics to model the gas components of both galaxies. The direct method of calculating the gravitational force between all particles provided a qualitative resolution of spatial structures up to 10 pc. The dwarf galaxy fell onto the gas and stellar discs of the main galaxy almost along a radial trajectory with a large eccentricity. This ensured that the dwarf crossed the disc of the main galaxy at each pericentric approach over a time interval of more than 9 billion years. We varied the gas mass and the initial orbital characteristics of the satellite over a wide range, studying the features of mass loss in the core. The presence of the initial gas component in a dwarf galaxy significantly affects the nature of the formation and evolution of the compact stellar core. The gas-rich satellite gives birth to a more compact elliptical galaxy compared to the merging gas-free dwarf galaxy. The initial gas content in the satellite also affects the internal rotation in the stripped nucleus. The simulated cE/UCD galaxies contained very little gas and dark matter at the end of their evolution.
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(This article belongs to the Special Issue Galactic Structure and Dynamics)
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Fueling Processes on (Sub-)kpc Scales
Galaxies 2023, 11(6), 120; https://doi.org/10.3390/galaxies11060120 - 13 Dec 2023
Abstract
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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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S0 Galaxies: Outer Gas Accretion through Tidal Interaction and Minor Merging
Galaxies 2023, 11(6), 119; https://doi.org/10.3390/galaxies11060119 - 08 Dec 2023
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To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the H emission line by using the scanning Fabry–Perot interferometer of the 6m telescope of the Special Astrophysical Observatory RAS. We
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To clarify the sources of outer gas accretion onto disk galaxies, we study the vicinity of four interacting galaxy systems in the H 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.
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Ionizing Spotlight of Active Galactic Nucleus
Galaxies 2023, 11(6), 118; https://doi.org/10.3390/galaxies11060118 - 07 Dec 2023
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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
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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 years.The role of modern narrow-band and integral-field surveys in these researches is also considered.
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Testing a Lepto-Hadronic Two-Zone Model with Extreme High-Synchrotron Peaked BL Lacs and Track-like High-Energy Neutrinos
Galaxies 2023, 11(6), 117; https://doi.org/10.3390/galaxies11060117 - 06 Dec 2023
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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
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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.
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On the Maximum Energy Release from Formation of Static Compact Objects
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Galaxies 2023, 11(6), 116; https://doi.org/10.3390/galaxies11060116 - 21 Nov 2023
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Type II Supernova 1987A (SN 1987A), observed in 1987, released an energy of 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
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Type II Supernova 1987A (SN 1987A), observed in 1987, released an energy of 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 . 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 . 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 ( ) might release an energy erg.
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Holographic Quantum-Foam Blurring Is Consistent with Observations of Gamma-Ray Burst GRB221009A
Galaxies 2023, 11(6), 115; https://doi.org/10.3390/galaxies11060115 - 17 Nov 2023
Abstract
Gamma-ray burst GRB221009A was of unprecedented brightness in the -rays and X-rays through to the far ultraviolet, allowing for identification within a host galaxy at redshift by multiple space and ground-based optical/near-infrared telescopes and enabling a first association—via cosmic-ray
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Gamma-ray burst GRB221009A was of unprecedented brightness in the -rays and X-rays through to the far ultraviolet, allowing for identification within a host galaxy at redshift 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 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.
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(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)
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A Study of the Properties and Dynamics of the Disk of Satellites in a Milky-Way-like Galaxy System
Galaxies 2023, 11(6), 114; https://doi.org/10.3390/galaxies11060114 - 16 Nov 2023
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
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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 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.
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(This article belongs to the Special Issue Galactic Structure and Dynamics)
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Quasiperiodic Oscillations and Dynamics of Test Particles around Regular-Kiselev Black Holes
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Galaxies 2023, 11(6), 113; https://doi.org/10.3390/galaxies11060113 - 16 Nov 2023
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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
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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.
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Exoplanets around Red Giants: Distribution and Habitability
Galaxies 2023, 11(6), 112; https://doi.org/10.3390/galaxies11060112 - 16 Nov 2023
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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
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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.
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Optimization of Quantum Noise in Space Gravitational-Wave Antenna DECIGO with Optical-Spring Quantum Locking Considering Mixture of Vacuum Fluctuations in Homodyne Detection
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, , , , , , , , , , , and
Galaxies 2023, 11(6), 111; https://doi.org/10.3390/galaxies11060111 - 09 Nov 2023
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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
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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 from to , 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.
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Simulated Radio and Neutrino Imaging of a Microquasar
Galaxies 2023, 11(6), 110; https://doi.org/10.3390/galaxies11060110 - 09 Nov 2023
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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
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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.
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On the Possible Asymmetry in Gamma Rays from Andromeda Due to Inverse Compton Scattering of Star Light on Electrons from Dark Matter Annihilation
Galaxies 2023, 11(6), 109; https://doi.org/10.3390/galaxies11060109 - 07 Nov 2023
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
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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.
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(This article belongs to the Special Issue Galactic Structure and Dynamics)
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The Structure of Micro-Variability in the WEBT BL Lacertae Observation
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Galaxies 2023, 11(6), 108; https://doi.org/10.3390/galaxies11060108 - 01 Nov 2023
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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
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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.
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Reference Array and Design Consideration for the Next-Generation Event Horizon Telescope
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, , , , , , , , , , , , , , , , , , , , , , , , , , , and add
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Galaxies 2023, 11(5), 107; https://doi.org/10.3390/galaxies11050107 - 18 Oct 2023
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We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program—the next-generation Event Horizon Telescope (ngEHT)—will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes
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We describe the process to design, architect, and implement a transformative enhancement of the Event Horizon Telescope (EHT). This program—the next-generation Event Horizon Telescope (ngEHT)—will form a networked global array of radio dishes capable of making high-fidelity real-time movies of supermassive black holes (SMBH) and their emanating jets. This builds upon the EHT principally by deploying additional modest-diameter dishes to optimized geographic locations to enhance the current global mm/submm wavelength Very Long Baseline Interferometric (VLBI) array, which has, to date, utilized mostly pre-existing radio telescopes. The ngEHT program further focuses on observing at three frequencies simultaneously for increased sensitivity and Fourier spatial frequency coverage. Here, the concept, science goals, design considerations, station siting, and instrument prototyping are discussed, and a preliminary reference array to be implemented in phases is described.
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(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)
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A Comprehensive Study of Soft X-ray Absorption Features in GX 13+1 Using XMM-Newton Observations
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Galaxies 2023, 11(5), 106; https://doi.org/10.3390/galaxies11050106 - 15 Oct 2023
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In this study, a comprehensive analysis of the reflection grating spectrometer (RGS) data (energy range 0.33 keV to 2.5 keV) of GX 13+1 from the XMM-Newton space observatory was conducted. Numerous absorption lines have been described in earlier publications, although the majority of
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In this study, a comprehensive analysis of the reflection grating spectrometer (RGS) data (energy range 0.33 keV to 2.5 keV) of GX 13+1 from the XMM-Newton space observatory was conducted. Numerous absorption lines have been described in earlier publications, although the majority of these investigations focused on the energy range between 3 keV and 10 keV. We considered all ten on-axis observations for spectral analysis, but during timing analysis, off-axis observations were also analysed. A fresh dip in off-axis observation 0122340701(B) was observed together with the previously reported dip in on-axis observation 0505480501(F). No burst or eclipsing was observed in any of the observations. The spectral analysis revealed the presence of the highly ionized elements, Si XIII 1s2–1s2p and 1s2–1s3p transitions with energies of 2.02 keV and 2.24 keV, respectively, as well as Mg XII 1s–6p transitions with energies of 1.91 keV and Al XIII 1s–4p transitions with energies of 2.15 keV. Before this study, no analyses of XMM-Newton data reported Mg XII and Al XIII elements. Moreover, the 1s–6p transitions of Mg XII and 1s–4p transitions of Al XIII were not even reported in any Chandra data analysis. The equivalent hydrogen column densities obtained (2.35 × 1022 cm−2 to 4.18 × 1022 cm−2) are consistent with previously reported values. The equivalent widths of neighbouring observations are found to be nearly the same. This supports us in suggesting that the absorptions may be due to the presence of an interstellar medium (ISM) in the line of sight (LOS) of the source.
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Three Dimensional Natures of Massive Star Envelopes
Galaxies 2023, 11(5), 105; https://doi.org/10.3390/galaxies11050105 - 11 Oct 2023
Cited by 1
Abstract
In this paper, we review our current understanding of the outer envelope structures of massive stars based on three-dimensional (3D) radiation hydrodynamic simulations. We briefly summarize the fundamental issues in constructing hydrostatic one-dimensional (1D) stellar evolution models when stellar luminosity approaches the Eddington
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In this paper, we review our current understanding of the outer envelope structures of massive stars based on three-dimensional (3D) radiation hydrodynamic simulations. We briefly summarize the fundamental issues in constructing hydrostatic one-dimensional (1D) stellar evolution models when stellar luminosity approaches the Eddington value. Radiation hydrodynamic simulations in 3D covering the mass range from to always find a dynamic envelope structure with the time-averaged radial profiles matching 1D models with an adjusted mixing-length parameter when convection is subsonic. Supersonic turbulence and episodic mass loss are generally found in 3D models when stellar luminosity is super-Eddington locally due to the opacity peaks and convection being inefficient. Turbulent pressure plays an important role in supporting the outer envelope, which makes the photosphere more extended than predictions from 1D models. Massive star lightcurves are always found to vary with a characteristic timescale consistent with the thermal time scale at the location of the iron opacity peak. The amplitude of the variability as well as the power spectrum can explain the commonly observed stochastic low-frequency variability of mass stars observed by TESS over a wide range of parameters in an HR diagram. The 3D simulations can also explain the ubiquitous macro-turbulence that is needed for spectroscopic fitting in massive stars. Implications of 3D simulations for improving 1D stellar evolution models are also discussed.
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(This article belongs to the Special Issue The Structure and Evolution of Stars)
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Complex Organics in Space: A Changing View of the Cosmos
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Galaxies 2023, 11(5), 104; https://doi.org/10.3390/galaxies11050104 - 08 Oct 2023
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Planetary explorations have revealed that complex organics are widely present in the solar system. Astronomical infrared spectroscopic observations have discovered that complex organics are synthesized in large quantities in planetary nebulae and distributed throughout the galaxy. Signatures of organics have been found in
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Planetary explorations have revealed that complex organics are widely present in the solar system. Astronomical infrared spectroscopic observations have discovered that complex organics are synthesized in large quantities in planetary nebulae and distributed throughout the galaxy. Signatures of organics have been found in distant galaxies, as early as 1.5 billion years after the Big Bang. A number of unsolved spectral phenomena such as diffuse interstellar bands, extended red emissions, 220 nm feature, and unidentified infrared emission bands are likely to originate from organics. In this paper, we discuss the possible chemical structures of the carriers of these unexplained phenomena, and how these organics are synthesized abiotically in the universe. We raise the possibility that the primordial solar system was enriched by complex organics synthesized and ejected by evolved stars. The implications of possible stellar organics in primordial Earth are also discussed.
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Signals in the Universe: Variable Stars and Transients as Physics Gauges
Guest Editors: Armando Arellano Ferro, Javier A. AhumadaDeadline: 31 March 2024
Special Issue in
Galaxies
From Cosmic Nurseries to Celestial Giants: Deciphering the Formation of High-Mass Stars
Guest Editors: Mengyao Liu, Yu ChengDeadline: 17 April 2024
Topical Collections
Topical Collection in
Galaxies
A Trip across the Universe: Our Present Knowledge and Future Perspectives
Collection Editor: Emilio Elizalde