oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Cosmic balloons  [PDF]
B. Holdom
Physics , 1993, DOI: 10.1103/PhysRevD.49.3844
Abstract: Cosmic balloons, consisting of relativistic particles trapped inside a spherical domain wall, may be created in the early universe. We calculate the balloon mass $M$ as a function of the radius $R$ and the energy density profile, $\rho (r)$, including the effects of gravity. At the maximum balloon mass $2GM/R\approx 0.52$ for any value of the mass density of the wall.
Radius-mass scaling laws for celestial bodies  [PDF]
R. Muradian,S. Carneiro,R. Marques
Physics , 1999,
Abstract: In this letter we establish a connection between two-exponent radius-mass power laws for cosmic objects and previously proposed two-exponent Regge-like spin-mass relations. A new, simplest method for establishing the coordinates of Chandrasekhar and Eddington points is proposed.
Measuring Neutron Star Mass and Radius with Three Mass-Radius Relations  [PDF]
C. M. Zhang,H. X. Yin,Y. Kojima,H. K. Chang,R. X. Xu,X. D. Li,B. Zhang,B. Kiziltan
Physics , 2006, DOI: 10.1111/j.1365-2966.2006.11133.x
Abstract: We propose to determine the mass and the radius of a neutron star (NS) using three measurable mass-radius relationships, namely the ``apparent'' radius inferred from neutron star thermal emission, the gravitational redshift inferred from the absorption lines, as well as the averaged stellar mass density inferred from the orbital Keplerian frequency derived from the kilohertz quasi periodic oscillation (kHz QPO) data. We apply the method to constrain the NS mass and the radius of the X-ray sources, 1E 1207.4-5209, Aql X-1 and EXO 0748-676.
Mass-radius relationships for exoplanets  [PDF]
Damian Swift,Jon Eggert,Damien Hicks,Sebastien Hamel,Kyle Caspersen,Eric Schwegler,Gilbert Collins,Nadine Nettelmann,Graeme Ackland
Physics , 2010, DOI: 10.1088/0004-637X/744/1/59
Abstract: For planets other than Earth, interpretation of the composition and structure depends largely on comparing the mass and radius with the composition expected given their distance from the parent star. The composition implies a mass-radius relation which relies heavily on equations of state calculated from electronic structure theory and measured experimentally on Earth. We lay out a method for deriving and testing equations of state, and deduce mass-radius and mass-pressure relations for key materials whose equation of state is reasonably well established, and for differentiated Fe/rock. We find that variations in the equation of state, such as may arise when extrapolating from low pressure data, can have significant effects on predicted mass- radius relations, and on planetary pressure profiles. The relations are compared with the observed masses and radii of planets and exoplanets. Kepler-10b is apparently 'Earth- like,' likely with a proportionately larger core than Earth's, nominally 2/3 of the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an Fe-based core which is likely to be proportionately smaller than Earth's. GJ 1214b lies between the mass-radius curves for H2O and CH4, suggesting an 'icy' composition with a relatively large core or a relatively large proportion of H2O. CoRoT-2b is less dense than the hydrogen relation, which could be explained by an anomalously high degree of heating or by higher than assumed atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation for hydrogen, suggesting the presence of a significant amount of matter of higher atomic number. CoRoT-3b lies close to the hydrogen relation. The pressure at the center of Kepler-10b is 1.5+1.2-1.0 TPa. The central pressure in CoRoT-7b is probably close to 0.8TPa, though may be up to 2TPa.
On the mass-radius relation of hot stellar systems  [PDF]
Mark Gieles,Holger Baumgardt,Douglas Heggie,Henny Lamers
Physics , 2010, DOI: 10.1111/j.1745-3933.2010.00919.x
Abstract: Most globular clusters have half-mass radii of a few pc with no apparent correlation with their masses. This is different from elliptical galaxies, for which the Faber-Jackson relation suggests a strong positive correlation between mass and radius. Objects that are somewhat in between globular clusters and low-mass galaxies, such as ultra-compact dwarf galaxies, have a mass-radius relation consistent with the extension of the relation for bright ellipticals. Here we show that at an age of 10 Gyr a break in the mass-radius relation at ~10^6 Msun is established because objects below this mass, i.e. globular clusters, have undergone expansion driven by stellar evolution and hard binaries. From numerical simulations we find that the combined energy production of these two effects in the core comes into balance with the flux of energy that is conducted across the half-mass radius by relaxation. An important property of this `balanced' evolution is that the cluster half-mass radius is independent of its initial value and is a function of the number of bound stars and the age only. It is therefore not possible to infer the initial mass-radius relation of globular clusters and we can only conclude that the present day properties are consistent with the hypothesis that all hot stellar systems formed with the same mass-radius relation and that globular clusters have moved away from this relation because of a Hubble time of stellar and dynamical evolution.
Cosmic Ray Investigation in the Stratosphere and Space: Results from Instruments on Russian Satellites and Balloons  [PDF]
Yu. I. Logachev,L. L. Lazutin,K. Kudela
Advances in Astronomy , 2013, DOI: 10.1155/2013/461717
Abstract: Selected activities aimed to investigate cosmic ray fluxes and to contribute to the understanding of the mechanisms behind, over a long-time period using space research tools in the former USSR/Russia and Slovakia, are reviewed, and some of the results obtained are presented. As the selection is connected with the institutes where the authors are working, it represents only a partial review of this wide topic. 1. Some Milestones until the Middle of the Last Century The investigation of cosmic rays began in 1900-1901, more than 100 years ago. During the first ten years the researchers were not aware that what they were studying were cosmic rays. All began at the time of measurements of the conductivity of various gases including the air, when some “residual” ionization, that is, a weak “dark current,” was observed even without ionizing sources. First publications of those experiments relate to the period of 1900-1901 [1–3]. One of the first researchers of the “dark current” was Charles Wilson, well known as the inventor of Wilson chamber (1911), which was widely used for studying various types of radiation, including cosmic rays. Later, in 1927, Wilson received the Nobel Prize in physics for this finding. Thanks to those experiments it became clear that at sea level some not intense but strongly penetrating radiation is always present (which was also observed in strongly shielded chambers). At the beginning it was thought that the radiation is emanating from the soil, similarly to Earth’s radioactivity, and that is why it must be declining above the Earth’s surface. However, the radiation was decreasing just up to the altitude about one km, while above this level its intensity was increasing. The fact that radiation intensity increases with altitude was discovered in 1912 after by the experiments of the Austrian physicist Hess [4], who measured radiation by ionization chamber up to more than 5?km. Hess called it “altitude radiation.” This name was used until 1925. The nature of that radiation was not clarified for a long time. Several hypotheses of its origin have been proposed (e.g., it originated in the upper layers of the atmosphere due to atmospheric electricity). Finally, the extraterrestrial origin of “altitude radiation” was proved by Millikan et al. (USA) in 1923-1924, who introduced the term “cosmic rays” [5, 6]. At that time Millikan was already awarded the Nobel Prize (in 1923 for the measurement of the charge of electron). Cosmic rays remained the “mystery effect” for a rather long time. This is argued by the fact that Nobel Prize for his
The mass and radius evolution of globular clusters in tidal fields  [PDF]
Mark Gieles
Physics , 2013,
Abstract: We present a simple theory for the evolution of initially compact clusters in a tidal field. The fundamental ingredient of the model is that a cluster conducts a constant fraction of its own energy through the half-mass radius by two-body interactions every half-mass relaxation time. This energy is produced in a self-regulative way in the core by an (unspecified) energy source. We find that the half-mass radius increases during the first part (roughly half) of the evolution and decreases in the second half, while the escape rate is constant and set by the tidal field. We present evolutionary tracks and isochrones for clusters in terms of cluster half-mass density, cluster mass and galacto-centric radius. We find substantial agreement between model isochrones and Milky Way globular cluster parameters, which suggests that there is a balance between the flow of energy and the central energy production for almost all globular clusters. We also find that the majority of the globular clusters are still expanding towards their tidal radius. Finally, a fast code for cluster evolution is presented.
Special point on the mass radius diagram of hybrid stars  [PDF]
A. V. Yudin,T. L. Razinkova,D. K. Nadyozhin,A. D. Dolgov
Physics , 2014, DOI: 10.1134/S1063773714040069
Abstract: An analytical study that explains the existence of a very small region on the mass radius diagram of hybrid stars where all of the lines representing the sequences of models with different constant values of the bag constant B intersect is presented. This circumstance is shown to be a consequence of the linear dependence of pressure on energy density in the quark cores of hybrid stars.
Mass-Radius Relation for Magnetic White Dwarfs  [PDF]
In-Saeng Suh,G. J. Mathews
Physics , 1999, DOI: 10.1086/308403
Abstract: Recently, several white dwarfs with very strong surface magnetic fields have been observed. In this paper we explore the possibility that such stars could have sufficiently strong internal fields to alter their structure. We obtain a revised white dwarf mass-radius relation in the presence of strong internal magnetic fields. We first derive the equation of state for a fully degenerate ideal electron gas in a magnetic field using an Euler-MacLaurin expansion. We use this to obtain the mass-radius relation for magnetic $^{4}$He, $^{12}$C, and $^{56}$Fe white dwarfs of uniform composition.
Methane Planets and their Mass-Radius Relation  [PDF]
Ravit Helled,Morris Podolak,Eran Vos
Physics , 2015, DOI: 10.1088/2041-8205/805/2/L11
Abstract: Knowledge of both the mass and radius of an exoplanet allows us to estimate its mean density, and therefore its composition. Exoplanets seem to fill a very large parameter space in terms of mass and composition, and unlike the solar-system's planets, exoplanets also have intermediate masses (~ 5 - 50 M_Earth) with various densities. In this letter, we investigate the behavior of the Mass-Radius relation for methane (CH_4) planets and show that when methane planets are massive enough (Mp >~ 15 M_Earth), the methane can dissociate and lead to a differentiated planet with a carbon core, a methane envelope, and a hydrogen atmosphere. The contribution of a rocky core to the behavior of CH_4 planet is considered as well. We also develop interior models for several detected intermediate-mass planets that could, in principle, be methane/methane-rich planets. The example of methane planets emphasizes the complexity of the Mass-Radius relation and the challenge involved in uniquely inferring the planetary composition.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.