Proper Size of the Visible Universe in FRW Metrics with Constant Spacetime Curvature

In this paper, we continue to examine the fundamental basis for the Friedmann-Robertson-Walker (FRW) metric and its application to cosmology, specifically addressing the question: What is the proper size of the visible universe? There are several ways of answering the question of size, though often with an incomplete understanding of how far light has actually traveled in reaching us today from the most remote sources. The difficulty usually arises from an inconsistent use of the coordinates, or an over-interpretation of the physical meaning of quantities such as the so-called proper distance R(t)=a(t)r, written in terms of the (unchanging) co-moving radius r and the universal expansion factor a(t). In this paper, we use the five non-trivial FRW metrics with constant spacetime curvature (i.e., the static FRW metrics, but excluding Minkowski) to prove that in static FRW spacetimes in which expansion began from an initial signularity, the visible universe today has a proper size equal to R_h(t_0/2), i.e., the gravitational horizon at half its current age. The exceptions are de Sitter and Lanczos, whose contents had pre-existing positions away from the origin. In so doing, we confirm earlier results showing the same phenomenon in a broad range of cosmologies, including LCDM, based on the numerical integration of null geodesic equations through an FRW metric.Comment: Accepted for publication in Classical and Quantum Gravit

The IWRP and Deaf Individuals: A Challenge to Excel

Non

Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A*

The evolution of an accretion disk can be influenced significantly by the deposition of mass and angular momentum by an infalling Bondi-Hoyle wind. Such a mass influx impacts the long-term behavior of the disk by providing additional sources of viscosity and heating. In this paper, we derive and solve the disk equations when these effects are taken into account. We present a survey of models with various wind configurations and demonstrate that the disk spectrum may then differ substantially from that of a standard alpha-disk. In particular, it is likely that a wind-fed disk has a significant infrared bump due to the deposition of energy in its outer region. We apply some of the results of our calculations to the Galactic Center black hole candidate Sgr A* and show that if a fossil disk is present in this source, it must have a very low viscosity parameter (alpha<10^-4) and the Bondi-Hoyle wind must be accreting with a very high specific angular momentum to prevent it from circularizing in the inner disk region where its impact would be most noticeable.Comment: accepted for The Astrophysical Journal, AAS LaTex, 20 pages, also available at http://www.astro.umd.edu/~hfalcke/publications.html#wintercep

Harga Diri Dan Interaksi Sosial Pada Remaja Panti Asuhan Dan Remaja Yang Tinggal Bersama Keluarga Di Kabupaten Purbalingga

Remaja memiliki kebutuhan yang tinggi untuk dapat diterima oleh kawan sebayanya, melalui kebutuhan tersebut terciptalah interaksi sosial. Komunikasi merupakan syarat terjadinya interaksi sosial, individu yang memiliki harga diri rendah akan mengalami kesulitan untuk mengomunikasikan gagasanya kepada orang-orang disekitar sehingga berpengaruh pada kemampuan interaksi sosial individu. Lingkungan dapat mempengaruhi tingkah laku individu termasuk salah satunya adalah interaksi sosial. Penelitian ini memiliki dua tujuan. Penelitian ini menggunakan harga diri sebagai variabel predictor dan interaksi sosial sebagai variabel kriterium. Tujuan penelitian ini adalah untuk melihat hubungan antara harga diri dan interaksi sosial pada remaja. Subjek dalam penelitian ini adalah remaja yang tinggal di panti asuhan dan tinggal bersama keluarga dengan kisaran usia 11-24 tahun. Jumlah sampel dalam penelitian ini adalah 349 remaja yang dipilih menggunakan teknik sampling cluster sampling. Analisis yang digunakan dalam penelitian ini menggunakan uji regresi linear sederhana dan uji beda independent t-test. Berdasarkan analisis statistik menggunakan uji regresi linear sederhana diperoleh koefisien korelasi sebesar 0,656 dengan p=0,000 (p < 0,05). Nilai koefisien korelasi menunjukan adanya hubungan antara harga diri dan interaksi sosial pada remaja

A fit to the simultaneous broadband spectrum of Cygnus X-1 using the transition disk model

We have used the transition disk model to fit the simultaneous broad band ($2-500$ keV) spectrum of Cygnus X-1 from OSSE and Ginga observations. In this model, the spectrum is produced by saturated Comptonization within the inner region of the accretion disk, where the temperature varies rapidly with radius. In an earlier attempt, we demonstrated the viability of this model by fitting the data from EXOSAT, XMPC balloon and OSSE observations, though these were not made simultaneously. Since the source is known to be variable, however, the results of this fit were not conclusive. In addition, since only once set of observations was used, the good agreement with the data could have been a chance occurrence. Here, we improve considerably upon our earlier analysis by considering four sets of simultaneous observations of Cygnus X-1, using an empirical model to obtain the disk temperature profile. The vertical structure is then obtained using this profile and we show that the analysis is self- consistent. We demonstrate conclusively that the transition disk spectrum is a better fit to the observations than that predicted by the soft photon Comptonization model. Since the temperature profile is obtained by fitting the data, the unknown viscosity mechanism need not be specified. The disk structure can then be used to infer the viscosity parameter $\alpha$, which appears to vary with radius and luminosity. This behavior can be understood if $\alpha$ depends intrinsically on the local parameters such as density, height and temperature. However, due to uncertainties in the radiative transfer, quantitative statements regarding the variation of $\alpha$ cannot yet be made.Comment: 8 figures. uses aasms4.sty, accepted by ApJ (Mar 98

Plasma Perturbations and Cosmic Microwave Background Anisotropy in the Linearly Expanding Milne-like Universe

We expose the scenarios of primordial baryon-photon plasma evolution within the framework of the Milne-like universe models. Recently, such models find a second wind and promise an inflation-free solution of a lot of cosmological puzzles including the cosmological constant one. Metric tensor perturbations are considered using the five-vectors theory of gravity admitting the Friedmann equation satisfied up to some constant. The Cosmic Microwave Background (CMB) spectrum is calculated qualitatively.Comment: 20 page

General Relativistic Flux Modulations from Disk Instabilities in Sagittarius A*

Near-IR and X-ray flares have been detected from the supermassive black hole Sgr A* at the center of our Galaxy with a (quasi)-period of ~17-20 minutes, suggesting an emission region only a few Schwarzschild radii above the event horizon. The latest X-ray flare, detected with XMM-Newton, is notable for its detailed lightcurve, yielding not only the highest quality period thus far, but also important structure reflecting the geometry of the emitting region. Recent MHD simulations of Sgr A*'s disk have demonstrated the growth of a Rossby wave instability, that enhances the accretion rate for several hours, possibly accounting for the observed flares. In this Letter, we carry out ray-tracing calculations in a Schwarzschild metric to determine as accurately as possible the lightcurve produced by general relativistic effects during such a disruption. We find that the Rossby wave induced spiral pattern in the disk is an excellent fit to the data, implying a disk inclination angle of ~77 deg. Note, however, that if this association is correct, the observed period is not due to the underlying Keplerian motion but, rather, to the pattern speed. The favorable comparison between the observed and simulated lightcurves provides important additional evidence that the flares are produced in Sgr A*'s inner disk.Comment: 5 Pages, 3 Figures, accepted for publication in ApJ Lette

The X-ray Ridge Surrounding Sgr A* at the Galactic Center

We present the first detailed simulation of the interaction between the supernova explosion that produced Sgr A East and the wind-swept inner ~ 2-pc region at the Galactic center. The passage of the supernova ejecta through this medium produces an X-ray ridge ~ 9'' to 15'' to the NE of the supermassive black hole Sagittarius A* (Sgr A*). We show that the morphology and X-ray intensity of this feature match very well with recently obtained Chandra images, and we infer a supernova remnant age of less than 2,000 years. This young age--a factor 3--4 lower than previous estimates--arises from our inclusion of stellar wind effects in the initial (pre-explosion) conditions in the medium. The supernova does not clear out the central ~ 0.2-pc region around Sgr~A* and does not significantly alter the accretion rate onto the central black hole upon passage through the Galactic center.Comment: 10 pages, 3 figures, submitted to ApJ

A Model of the EGRET Source at the Galactic Center: Inverse Compton Scattering Within Sgr A East and its Halo

Continuum low-frequency radio observations of the Galactic Center reveal the presence of two prominent radio sources, Sgr A East and its surrounding Halo, containing non-thermal particle distributions with power-law indices around 2.5-3.3 and 2.4, respectively. The central 1-2 pc region is also a source of intense (stellar) UV and (dust-reprocessed) far-IR radiation that bathes these extended synchrotron-emitting structures. A recent detection of gamma-rays (2EGJ1746-2852) from within around 1 degree of the Galactic Center by EGRET onboard the Compton GRO shows that the emission from this environment extends to very high energies. We suggest that inverse Compton scatterings between the power-law electrons inferred from the radio properties of Sgr A East and its Halo, and the UV and IR photons from the nucleus, may account for the possibly diffuse gamma-ray source as well. We show that both particle distributions may be contributing to the gamma-ray emission, though their relevant strength depends on the actual physical properties (such as the magnetic field intensity) in each source. If this picture is correct, the high-energy source at the Galactic Center is extended over several arcminutes, which can be tested with thenext generation of gamma-ray and hard X-ray missions.Comment: latex, 14 pages, 3 figures (accepted for publication in ApJ