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Symmetry
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Astronomy and Symmetry
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Astronomy and Symmetry

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 12458

Special Issue Editor

Dr. Sandor Frey

E-Mail Website
Guest Editor
Research Centre for Astronomy and Earth Sciences, Konkoly Observatory, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
Interests: astronomy; space geodesy

Special Issue Information

Dear Colleagues,

From meteoritic crystals to giant double-lobed radio galaxies, from light curves of transiting extrasolar planets to gravitationally-lensed images of distant quasars, from jets in young stellar objects to the morphology of planetary nebulae, from celestial mechanics to cosmology, symmetry is ubiquitous in the Universe, and therefore in astronomical research. This Special Issue of the interdisciplinary journal Symmetry aims to collect observational and theoretical contributions related to symmetry (or, actually, the lack of it) from various fields of astronomy, astrophysics, and closely-related disciplines.

Dr. Sandor Frey
Guest Editor

Manuscript Submission Information

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 submissions that pass pre-check are 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. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). 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.

Published Papers (6 papers)

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Editorial

Jump to: Research

4 pages, 192 KiB  
Editorial
Special Issue on Astronomy and Symmetry
by Sándor Frey
Symmetry 2022, 14(8), 1614; https://doi.org/10.3390/sym14081614 - 5 Aug 2022
Viewed by 877
Abstract
Astronomy is undoubtedly one of the oldest branches of natural sciences [...] Full article
(This article belongs to the Special Issue Astronomy and Symmetry)

Research

Jump to: Editorial

31 pages, 48288 KiB  
Article
Quantification of Sub-Solar Star Ages from the Symmetry of Conjugate Histograms of Spin Period and Angular Velocity
by Robert E. Criss and Anne M. Hofmeister
Symmetry 2021, 13(8), 1519; https://doi.org/10.3390/sym13081519 - 18 Aug 2021
Cited by 1 | Viewed by 2125
Abstract
Empirical laws proposed for the decline in star spin with time have heretofore been tested using ambiguous fitting models. We develop an analytical inverse model that uses histogram data to unequivocally determine the physical law governing how dwarf star spin depends on time [...] Read more.
Empirical laws proposed for the decline in star spin with time have heretofore been tested using ambiguous fitting models. We develop an analytical inverse model that uses histogram data to unequivocally determine the physical law governing how dwarf star spin depends on time (t) and mass (M). We analyze shapes of paired histograms of axial rotation period (П) and angular velocity (ω = 2π/П) to utilize the fact that a variable and its reciprocal are governed by the same physics. Copious data on open clusters are used to test the formula ∂ω/∂t ∝ − ωn where n is unrestricted, and thus covers diverse possibilities. Histogram conjugates for each of 15 clusters with 120 to 812 measurements provide n = 1.13 ± 0.19. Results are independent of initial spin rate, bin size, cluster parameters, and star mass. Notably, 11 large clusters with mostly M-types yield fits with n = 1.07 ± 0.12. Associations behave similarly. Only exponential decay (n = 1) explains the similar shapes of the conjugate histograms for the spin period and angular velocity, despite the asymmetric (inverse) relationship of these variables. This rate law is consistent with viscous dissipation. Forward modeling confirms that n is near unity and further shows that coeval formation of all stars in a cluster does not occur. We therefore explore a constant rate of star production, which is reasonable for tiny stars. Inverse models show that episodic production increases with mass, but is unimportant below ~0.55 MSun. We infer star and cluster ages, and find that star production becomes less regular with time, as interstellar gas and dust are progressively depleted. Our new analytical approach of extracting a physical law from conjugate histograms is general and widely applicable. Full article
(This article belongs to the Special Issue Astronomy and Symmetry)
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22 pages, 5662 KiB  
Article
Constraints on Newtonian Interplanetary Point-Mass Interactions in Multicomponent Systems from the Symmetry of Their Cycles
by Anne M. Hofmeister and Everett M. Criss
Symmetry 2021, 13(5), 846; https://doi.org/10.3390/sym13050846 - 11 May 2021
Cited by 4 | Viewed by 2036
Abstract
Interplanetary interactions are the largest forces in our Solar System that disturb the planets from their elliptical orbits around the Sun, yet are weak (<10−3 Solar). Currently, these perturbations are computed in pairs using Hill’s model for steady-state, central forces between one [...] Read more.
Interplanetary interactions are the largest forces in our Solar System that disturb the planets from their elliptical orbits around the Sun, yet are weak (<10−3 Solar). Currently, these perturbations are computed in pairs using Hill’s model for steady-state, central forces between one circular and one elliptical ring of mass. However, forces between rings are not central. To represent interplanetary interactions, which are transient, time-dependent, and cyclical, we build upon Newton’s model of interacting point-mass pairs, focusing on circular orbits of the eight largest bodies. To probe general and evolutionary behavior, we present analytical and numerical models of the interplanetary forces and torques generated during the planetary interaction cycles. From symmetry, over a planetary interaction cycle, radial forces dominate while tangential forces average to zero. Our calculations show that orbital perturbations require millennia to quantify, but observations are only over ~165 years. Furthermore, these observations are compromised because they are predominantly made from Earth, whose geocenter occupies a complex, non-Keplerian orbit. Eccentricity and inclination data are reliable and suggest that interplanetary interactions have drawn orbital planes together while elongating the orbits of the two smallest planets. This finding is consistent with conservation principles governing the eight planets, which formed as a system and evolve as a system. Full article
(This article belongs to the Special Issue Astronomy and Symmetry)
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8 pages, 551 KiB  
Article
Planetary Systems and the Hidden Symmetries of the Kepler Problem
by József Cseh
Symmetry 2020, 12(12), 2109; https://doi.org/10.3390/sym12122109 - 18 Dec 2020
Cited by 2 | Viewed by 2155
Abstract
The question of whether the solar distances of the planetary system follow a regular sequence was raised by Kepler more than 400 years ago. He could not prove his expectation, inasmuch as the planetary orbits are not transformed into each other by the [...] Read more.
The question of whether the solar distances of the planetary system follow a regular sequence was raised by Kepler more than 400 years ago. He could not prove his expectation, inasmuch as the planetary orbits are not transformed into each other by the regular polyhedra. In 1989, Barut proposed another relation, which was inspired by the hidden symmetry of the Kepler problem. It was found to be approximately valid for our Solar System. Here, we investigate if exoplanet systems follow this rule. We find that the symmetry-governed sequence is valid in several systems. It is very unlikely that the observed regularity is by chance; therefore, our findings give support to Kepler’s guess, although with a different transformation rule. Full article
(This article belongs to the Special Issue Astronomy and Symmetry)
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16 pages, 980 KiB  
Article
The Axisymmetric Central Configurations of the Four-Body Problem with Three Equal Masses
by Emese Kővári and Bálint Érdi
Symmetry 2020, 12(4), 648; https://doi.org/10.3390/sym12040648 - 20 Apr 2020
Cited by 2 | Viewed by 2086
Abstract
In the studied axisymmetric case of the central four-body problem, the axis of symmetry is defined by two unequal-mass bodies, while the other two bodies are situated symmetrically with respect to this axis and have equal masses. Here, we consider a special case [...] Read more.
In the studied axisymmetric case of the central four-body problem, the axis of symmetry is defined by two unequal-mass bodies, while the other two bodies are situated symmetrically with respect to this axis and have equal masses. Here, we consider a special case of the problem and assume that three of the masses are equal. Using a recently found analytical solution of the general case, we formulate the equations of condition for three equal masses analytically and solve them numerically. A complete description of the problem is given by providing both the coordinates and masses of the bodies. We show furthermore how the three-equal-mass solutions are related to the general case in the coordinate space. The physical aspects of the configurations are also studied and discussed. Full article
(This article belongs to the Special Issue Astronomy and Symmetry)
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13 pages, 350 KiB  
Article
High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars
by Máté Krezinger, Sándor Frey, Zsolt Paragi and Roger Deane
Symmetry 2020, 12(4), 527; https://doi.org/10.3390/sym12040527 - 3 Apr 2020
Cited by 6 | Viewed by 1932
Abstract
Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to [...] Read more.
Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI). Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026–0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026−0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future. Full article
(This article belongs to the Special Issue Astronomy and Symmetry)
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