It was confirmed that there is a strong linear correlation between the thermal far-infrared (FIR) and non-thermal radio emission of the star-forming galaxies. Recent works based on this correlation over large redshifts have shown that the correlation is evolving towards higher redshifts. In this paper, possible physical causes that lead to the evolution of this correlation are explored. One possible cause is that the interaction between galaxies is responsible for this behavior. We used the morphology of galaxies, as an indicator of past or present interactions, because it is generally known that the irregular morphology of galaxies is a consequence of collisions or close approaches. To test this hypothesis, a sample of dusty star-forming galaxies up to a redshift z = 3:5 from the COSMOS field has been selected. The sample has been divided, according to the morphological type, into two subsamples (disk and irregular galaxies), and the evolution of the correlation with redshift has been analyzed separately for both of them. It was found that in both subsamples there is no indication for the redshift evolution of the FIR-radio correlation. However, it was also found that the mean correlation parameter, qFIR, is lower in irregular galaxies, which may indicate that they can still affect the evolution of the correlation if their abundance in the sample increases towards higher redshifts. Disk galaxies, which statistically dominate the sample, may be responsible for the lack of this evolution. On the other hand, a fundamental problem with optically determined morphology is the dust obscuration in massive galaxies at z > 2. To test the idea that interacting galaxies are responsible for redshift evolution of the FIR-radio correlation, it is, necessary to analyze a much larger sample for which the morphology has been determined, taking into account the VLA and ALMA imaging in addition to optical images, and which contains a higher fraction of irregular galaxies. Finally, it was also found that the qFIR parameter and its evolution are very sensitive to the radio spectral index above z > 1 and that its misinterpretation and taking a constant value of ? = 0:7 may be responsible for the observed evolution of the correlation.
{"title":"Does the fir-radio correlation evolve with redshift in irregular and disk galaxies?","authors":"M. Pavlovic","doi":"10.2298/saj2103015p","DOIUrl":"https://doi.org/10.2298/saj2103015p","url":null,"abstract":"It was confirmed that there is a strong linear correlation between the thermal far-infrared (FIR) and non-thermal radio emission of the star-forming galaxies. Recent works based on this correlation over large redshifts have shown that the correlation is evolving towards higher redshifts. In this paper, possible physical causes that lead to the evolution of this correlation are explored. One possible cause is that the interaction between galaxies is responsible for this behavior. We used the morphology of galaxies, as an indicator of past or present interactions, because it is generally known that the irregular morphology of galaxies is a consequence of collisions or close approaches. To test this hypothesis, a sample of dusty star-forming galaxies up to a redshift z = 3:5 from the COSMOS field has been selected. The sample has been divided, according to the morphological type, into two subsamples (disk and irregular galaxies), and the evolution of the correlation with redshift has been analyzed separately for both of them. It was found that in both subsamples there is no indication for the redshift evolution of the FIR-radio correlation. However, it was also found that the mean correlation parameter, qFIR, is lower in irregular galaxies, which may indicate that they can still affect the evolution of the correlation if their abundance in the sample increases towards higher redshifts. Disk galaxies, which statistically dominate the sample, may be responsible for the lack of this evolution. On the other hand, a fundamental problem with optically determined morphology is the dust obscuration in massive galaxies at z > 2. To test the idea that interacting galaxies are responsible for redshift evolution of the FIR-radio correlation, it is, necessary to analyze a much larger sample for which the morphology has been determined, taking into account the VLA and ALMA imaging in addition to optical images, and which contains a higher fraction of irregular galaxies. Finally, it was also found that the qFIR parameter and its evolution are very sensitive to the radio spectral index above z > 1 and that its misinterpretation and taking a constant value of ? = 0:7 may be responsible for the observed evolution of the correlation.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674505","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The photometry of the binary star BX And (HIP 10027) is performed during several nights in October and November 2019, and October 2020 using B, V, and R Johnson-Cousins filters in Dr. Mojtahedi Observatory of the University of Birjand. Astronomical image processing and data reduction are performed by the IRIS software and light curves are obtained. These curves, along with the radial velocity data of the binary star, are analyzed by the Phoebe program to determine the physical and geometric parameters of the system. The evolutionary state of this system is investigated using the Hertzsprung-Russell (H-R) and density vs color index diagrams. The O-C curve is plotted using the eclipse times obtained in this study and those reported in the literature. By fitting a quadratic function to this curve, a new linear ephemeris is obtained for the system, and the mass transfer rate between the components of the system is determined. A periodic behavior is observed in the residuals, after subtracting the quadratic function from the O-C curve. These periodic changes are attributed to the presence of a third component in the system. The parameters of the third component are determined by fitting the light-time function to the residuals curve.
{"title":"Photometry, light curve solution and period study of contact binary BX And","authors":"M. Partovi, A. Abedi, K. Y. Roobiat","doi":"10.2298/saj2103029p","DOIUrl":"https://doi.org/10.2298/saj2103029p","url":null,"abstract":"The photometry of the binary star BX And (HIP 10027) is performed during several nights in October and November 2019, and October 2020 using B, V, and R Johnson-Cousins filters in Dr. Mojtahedi Observatory of the University of Birjand. Astronomical image processing and data reduction are performed by the IRIS software and light curves are obtained. These curves, along with the radial velocity data of the binary star, are analyzed by the Phoebe program to determine the physical and geometric parameters of the system. The evolutionary state of this system is investigated using the Hertzsprung-Russell (H-R) and density vs color index diagrams. The O-C curve is plotted using the eclipse times obtained in this study and those reported in the literature. By fitting a quadratic function to this curve, a new linear ephemeris is obtained for the system, and the mass transfer rate between the components of the system is determined. A periodic behavior is observed in the residuals, after subtracting the quadratic function from the O-C curve. These periodic changes are attributed to the presence of a third component in the system. The parameters of the third component are determined by fitting the light-time function to the residuals curve.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Vchkova-Bebekovska, N. Todorović, A. Kostov, Z. Donchev, G. Borisov, G. Apostolovska
The asteroid (1986 QY4) 4940 Polenov is the first Solar system object whose 3D shape is determined using the observations from the newly built Astronomical Station Vidojevica (ASV). Here we present the results of photometric observations for Polenov, gathered from the ASV, and from the Bulgarian National Astronomical Observatory (BNAO) Rozhen, during 2014, 2019 and 2020 apparitions. Polenov is a 17.8km object located in the outer part of the main belt and belongs to the asteroid family Themis. We have determined the lightcurves, the synodic period of 4.161?0.001 h, as well as the solution for the shape and spin axis. Using the lightcurve inversion method, the combination of our lightcurves and the sparse data from ATLAS{HKO and ATLAS-MLO, we also found the sidereal period, indicating a retrograde rotation of the asteroid, with two possible mirrored pole solutions. The ratio of the largest to smallest reecting surface is about 1.4. In addition, we studied the dynamical properties of the asteroid and obtained a long stability time that exceeds 0.4 Gyrs.
{"title":"The physical and dynamical characteristics of the asteroid 4940 Polenov","authors":"E. Vchkova-Bebekovska, N. Todorović, A. Kostov, Z. Donchev, G. Borisov, G. Apostolovska","doi":"10.2298/saj2102039v","DOIUrl":"https://doi.org/10.2298/saj2102039v","url":null,"abstract":"The asteroid (1986 QY4) 4940 Polenov is the first Solar system object whose 3D shape is determined using the observations from the newly built Astronomical Station Vidojevica (ASV). Here we present the results of photometric observations for Polenov, gathered from the ASV, and from the Bulgarian National Astronomical Observatory (BNAO) Rozhen, during 2014, 2019 and 2020 apparitions. Polenov is a 17.8km object located in the outer part of the main belt and belongs to the asteroid family Themis. We have determined the lightcurves, the synodic period of 4.161?0.001 h, as well as the solution for the shape and spin axis. Using the lightcurve inversion method, the combination of our lightcurves and the sparse data from ATLAS{HKO and ATLAS-MLO, we also found the sidereal period, indicating a retrograde rotation of the asteroid, with two possible mirrored pole solutions. The ratio of the largest to smallest reecting surface is about 1.4. In addition, we studied the dynamical properties of the asteroid and obtained a long stability time that exceeds 0.4 Gyrs.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"42 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents detailed evolutionary models of low-mass binary systems (1.25 + 1 M?) with initial orbital periods of 10, 50 and 100 days and accretion efficiency of 10%, 20%, 50%, and a conservative assumption. All models are calculated with the MESA (Modules for Experiments in Stellar Astrophysics) evolutionary code. We show that such binary systems can evolve via a stable Case B mass transfer into long period helium white dwarf systems.
{"title":"Influence of the initial orbital period and accretion efficiency on the low-mass binary evolution","authors":"J. Petrovic","doi":"10.2298/saj2102025p","DOIUrl":"https://doi.org/10.2298/saj2102025p","url":null,"abstract":"This paper presents detailed evolutionary models of low-mass binary systems (1.25 + 1 M?) with initial orbital periods of 10, 50 and 100 days and accretion efficiency of 10%, 20%, 50%, and a conservative assumption. All models are calculated with the MESA (Modules for Experiments in Stellar Astrophysics) evolutionary code. We show that such binary systems can evolve via a stable Case B mass transfer into long period helium white dwarf systems.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present results based on analysis of the currently available 29.86 ks Chandra data on the Bright Group-Centered Galaxy (BGG) NGC 5846 of G50 group. A pair of X-ray cavities have been detected within a radius ? 1 kpc along the North-East and South-West directions. The analysis yielded the average cavity energy, ages and mechanical power equal to ~ 3:1 x 1048 erg, 0:61 x 107 yr and, 3:78 x 1041 erg s-1, respectively. The luminosity of X-ray emitting gas within the cooling radius (20 kpc) was found to be 2.4 x 1041 erg s??1, in agreement with the mechanical cavity power. The ratio of radio luminosity to mechanical cavity power is found to be 10??4. The Bondi accretion rate of the central supermassive black hole (SMBH) is ~ 5:95 x 10-5 M? yr-1 and the black-hole mass derived using the Bondi-accretion rate was found to be ~ 3:74 x 108 M?.
我们的研究结果是基于对G50群中明亮群中心星系NGC 5846的29.86 k钱德拉数据的分析。在一个半径内发现了一对x射线空洞。沿东北及西南方向每小时1公里。分析得出平均空腔能量、年龄和机械功率分别为~ 3:1 × 1048 erg、0:61 × 107 yr和3:78 × 1041 erg s-1。在冷却半径(20kpc)内，x射线发射气体的光度为2.4 x 1041 erg s?1、符合机械腔功率。无线电光度与机械腔功率之比为10??4。中心超大质量黑洞(SMBH)的邦迪吸积速率为~ 5:95 x 10-5 M?用bondi吸积率计算得到的黑洞质量为~ 3:74 x 108 M?
{"title":"X-ray cavities in the G50 bright group-centered galaxy NGC 5846","authors":"A. Kyadampure, N. Vagshette, M. Patil","doi":"10.2298/saj2102017k","DOIUrl":"https://doi.org/10.2298/saj2102017k","url":null,"abstract":"We present results based on analysis of the currently available 29.86 ks Chandra data on the Bright Group-Centered Galaxy (BGG) NGC 5846 of G50 group. A pair of X-ray cavities have been detected within a radius ? 1 kpc along the North-East and South-West directions. The analysis yielded the average cavity energy, ages and mechanical power equal to ~ 3:1 x 1048 erg, 0:61 x 107 yr and, 3:78 x 1041 erg s-1, respectively. The luminosity of X-ray emitting gas within the cooling radius (20 kpc) was found to be 2.4 x 1041 erg s??1, in agreement with the mechanical cavity power. The ratio of radio luminosity to mechanical cavity power is found to be 10??4. The Bondi accretion rate of the central supermassive black hole (SMBH) is ~ 5:95 x 10-5 M? yr-1 and the black-hole mass derived using the Bondi-accretion rate was found to be ~ 3:74 x 108 M?.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Gaia DR2 reference frame should be without relative rotation to the quasars (QSOs) and consistent with the International Celestial Reference System (ICRS). For the faint part of DR2 (stars with Gaia magnitude G ? 16) that task was done via Gaia's observations of QSOs (G ? 17 mag), but the bright DR2 (G ? 13 mag) is difficult to validate and it rotates relative to the faint DR2 at rate of the order of 0.1 mas/yr. Very bright DR2 stars (G ? 6 mag) mostly have inferior astrometry. Here, the aim is to determine two spin components (?X and ?Y) of the bright DR2 using International Latitude Service (ILS, for 387 stars) and independent latitude stations (INDLS, for 682 stars) catalogs of proper motion in declination ??; both are referred to the Hipparcos reference frame and their stars are mostly from 4 to 8 mag in the V-band (critical part of DR2). Also, using the new Hipparcos (NHIP) values ?? for ILS and INDLS stars, we can see that the merit of the ILS and INDLS is the long time baseline (?t ? 90 years) important for ?? because the standard deviation of ?? is opposite to ?t. Applying the least squares method (LSM) to the differences of ?? between two catalogs (ILS-DR2, INDLS-DR2, etc.), our results support the mentioned spin. The 3? criterion and Tukey's fences method were used to reject some stars, the Abbe criterion to explain the variability in ILS-DR2 and other ?? differences, and the Shapiro-Wilk test to check the standard distribution of differences. The obtained ?Y is significant at the 2 ? level, and the ILS and INDLS catalogs could be useful for validation of the bright reference frame of Gaia DR2.
{"title":"Independent analysis of γδ data of ILS and INDLS catalogs to obtain the spin of the bright Gaia DR2 reference frame","authors":"G. Damljanovic, M. Stojanovic, J. Aleksic","doi":"10.2298/saj210428002d","DOIUrl":"https://doi.org/10.2298/saj210428002d","url":null,"abstract":"The Gaia DR2 reference frame should be without relative rotation to the quasars (QSOs) and consistent with the International Celestial Reference System (ICRS). For the faint part of DR2 (stars with Gaia magnitude G ? 16) that task was done via Gaia's observations of QSOs (G ? 17 mag), but the bright DR2 (G ? 13 mag) is difficult to validate and it rotates relative to the faint DR2 at rate of the order of 0.1 mas/yr. Very bright DR2 stars (G ? 6 mag) mostly have inferior astrometry. Here, the aim is to determine two spin components (?X and ?Y) of the bright DR2 using International Latitude Service (ILS, for 387 stars) and independent latitude stations (INDLS, for 682 stars) catalogs of proper motion in declination ??; both are referred to the Hipparcos reference frame and their stars are mostly from 4 to 8 mag in the V-band (critical part of DR2). Also, using the new Hipparcos (NHIP) values ?? for ILS and INDLS stars, we can see that the merit of the ILS and INDLS is the long time baseline (?t ? 90 years) important for ?? because the standard deviation of ?? is opposite to ?t. Applying the least squares method (LSM) to the differences of ?? between two catalogs (ILS-DR2, INDLS-DR2, etc.), our results support the mentioned spin. The 3? criterion and Tukey's fences method were used to reject some stars, the Abbe criterion to explain the variability in ILS-DR2 and other ?? differences, and the Shapiro-Wilk test to check the standard distribution of differences. The obtained ?Y is significant at the 2 ? level, and the ILS and INDLS catalogs could be useful for validation of the bright reference frame of Gaia DR2.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"68674983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the paper by Jurkovic (2018), a reference is missing from the list of References: Pietrinferni et al. (2004). Also, in Acknowledgements a sentence was supposed to be added: "This work has made use of BaSTI web tools."
在Jurkovic(2018)的论文中，参考文献列表中缺少参考文献:pietrinterni et al.(2004)。此外，在致谢中应该加上一句话:“这项工作使用了BaSTI网络工具。”链接到更正后的文章10.2298/SAJ180316002J
{"title":"Corrigendum: Anomalous Cepheids discovered in a sample of galactic short period type II Cepheids (Serb. Astron. J. - 197 (2018), 13)","authors":"M. Jurkovic","doi":"10.2298/saj2001059e","DOIUrl":"https://doi.org/10.2298/saj2001059e","url":null,"abstract":"In the paper by Jurkovic (2018), a reference is missing from the list of\u0000 References: Pietrinferni et al. (2004). Also, in Acknowledgements a sentence\u0000 was supposed to be added: \"This work has made use of BaSTI web tools.\" <br><br><font color=\"red\"><b> Link to the corrected article <u><a href=\"http://dx.doi.org/10.2298/SAJ180316002J\">10.2298/SAJ180316002J</a></b></u>","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"201 1","pages":"59"},"PeriodicalIF":0.5,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43693136","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the paper by Wright (2020), due to an editing error, Footnote 2 contains an incorrect citation. The intended meaning of the relevant parts of the footnote is as follows: As detailed in Gray (2020), many authors who discuss an extension of Kardashev's scale to noninteger values cite Carl Sagan's book The Cosmic Connection (Sagan 1973a), which has no explicit equation but describes one implicitly with some characteristic values. Wright et al. (2014) incorrectly cite an Icarus article by Sagan (1973b), which discusses the integer version of the scale but not noninteger extensions. In Table 1, the definition of s should read: Probability a photon emitted by inner surface of the Dyson sphere does not immediately strike the star : : : On page 7 immediately after Eq. (25), the end of the sentence should be: : : : represents the probability that a photon emitted from or reected by the interior of the sphere in a random direction will not strike the star before it strikes the sphere again. Eq. (23) should have units of g/m2, not g/cm2. Similarly, on page 15, col. 2, line 13, the units should be g/m2 (consistent with correction for Eq. (23)), not g/cm3. Link to the corrected article 10.2298/SAJ2000001W
{"title":"Erratum: Dyson spheres (Serb. Astron. J. - 200 (2020), 1)","authors":"J. Wright","doi":"10.2298/saj2001061e","DOIUrl":"https://doi.org/10.2298/saj2001061e","url":null,"abstract":"In the paper by Wright (2020), due to an editing error, Footnote 2 contains\u0000 an incorrect citation. The intended meaning of the relevant parts of the\u0000 footnote is as follows: As detailed in Gray (2020), many authors who discuss\u0000 an extension of Kardashev's scale to noninteger values cite Carl Sagan's book\u0000 The Cosmic Connection (Sagan 1973a), which has no explicit equation but\u0000 describes one implicitly with some characteristic values. Wright et al.\u0000 (2014) incorrectly cite an Icarus article by Sagan (1973b), which discusses\u0000 the integer version of the scale but not noninteger extensions. In Table 1,\u0000 the definition of s should read: Probability a photon emitted by inner\u0000 surface of the Dyson sphere does not immediately strike the star : : : On\u0000 page 7 immediately after Eq. (25), the end of the sentence should be: : : :\u0000 represents the probability that a photon emitted from or reected by the\u0000 interior of the sphere in a random direction will not strike the star before\u0000 it strikes the sphere again. Eq. (23) should have units of g/m2, not g/cm2.\u0000 Similarly, on page 15, col. 2, line 13, the units should be g/m2 (consistent\u0000 with correction for Eq. (23)), not g/cm3. Link to the corrected article 10.2298/SAJ2000001W","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"201 1","pages":"61"},"PeriodicalIF":0.5,"publicationDate":"2020-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45526626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
I review the origins and development of the idea of Dyson spheres, their purpose, their engineering, and their detectability. I explicate the ways in which the popular imagining of them as monolithic objects would make them dynamically unstable under gravity and radiation pressure, and mechanically unstable to buckling. I develop a model for the radiative coupling between a star and large amounts of material orbiting it, and connect the observational features of a star plus Dyson sphere system to the gross radiative properties of the sphere itself. I discuss the still-unexplored problem of the effects of radiative feedback on the central star's structure and luminosity. Finally, I discuss the optimal sizes of Dyson spheres under various assumptions about their purpose as sources of low-entropy emission, dissipative work, or computation.
{"title":"Dyson spheres","authors":"J. Wright","doi":"10.2298/SAJ2000001W","DOIUrl":"https://doi.org/10.2298/SAJ2000001W","url":null,"abstract":"I review the origins and development of the idea of Dyson spheres, their\u0000 purpose, their engineering, and their detectability. I explicate the ways in\u0000 which the popular imagining of them as monolithic objects would make them\u0000 dynamically unstable under gravity and radiation pressure, and mechanically\u0000 unstable to buckling. I develop a model for the radiative coupling between a\u0000 star and large amounts of material orbiting it, and connect the\u0000 observational features of a star plus Dyson sphere system to the gross\u0000 radiative properties of the sphere itself. I discuss the still-unexplored\u0000 problem of the effects of radiative feedback on the central star's structure\u0000 and luminosity. Finally, I discuss the optimal sizes of Dyson spheres under\u0000 various assumptions about their purpose as sources of low-entropy emission,\u0000 dissipative work, or computation.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2020-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45949681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
There have been tantalizing indications from many quarters of physical cosmology that we are living in the multiverse – a huge set of cosmological domains (“universes”). What is the structure of this larger whole is an entirely open problem on the interface between physics and metaphysics. A goal of the present paper is to draw attention to the connection between this problem and an old and celebrated puzzle in mathematical physics. Among the unresolved problems David Hilbert posed in 1900 as a challenge for the dawning century, none is more philosophically controversial than the Sixth Problem, requiring the axiomatization of physical theories. In the new century and the new millennium, this problem has remained a challenge, usually swept under the rug as “not belonging to mathematics” (as if that impacts its epistemical status) or simply “unresolved”. Recent radical ontological/cosmological hypothesis of Max Tegmark, identifying mathematical and physical structures, might shed some new light onto this allegedly antiquated subject: it might be the case that the problem has already been solved, insofar we have formalized mathematical structures! While this can be seen as “cutting the Gordian knot” rather than patiently resolving the issue, we suggest that there are several advantages to taking Tegmark’s solution seriously, notably in the domain of (future) physics of the observer.
{"title":"Cosmology and Hilbert's sixth problem","authors":"M. Ćirković","doi":"10.2298/saj2000043c","DOIUrl":"https://doi.org/10.2298/saj2000043c","url":null,"abstract":"There have been tantalizing indications from many quarters of physical cosmology that we are living in the multiverse – a huge set of cosmological domains (“universes”). What is the structure of this larger whole is an entirely open problem on the interface between physics and metaphysics. A goal of the present paper is to draw attention to the connection between this problem and an old and celebrated puzzle in mathematical physics. Among the unresolved problems David Hilbert posed in 1900 as a challenge for the dawning century, none is more philosophically controversial than the Sixth Problem, requiring the axiomatization of physical theories. In the new century and the new millennium, this problem has remained a challenge, usually swept under the rug as “not belonging to mathematics” (as if that impacts its epistemical status) or simply “unresolved”. Recent radical ontological/cosmological hypothesis of Max Tegmark, identifying mathematical and physical structures, might shed some new light onto this allegedly antiquated subject: it might be the case that the problem has already been solved, insofar we have formalized mathematical structures! While this can be seen as “cutting the Gordian knot” rather than patiently resolving the issue, we suggest that there are several advantages to taking Tegmark’s solution seriously, notably in the domain of (future) physics of the observer.","PeriodicalId":48878,"journal":{"name":"Serbian Astronomical Journal","volume":"200 1","pages":"43-49"},"PeriodicalIF":0.5,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49507347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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