Advances in Astronomy 

About: Advances in Astronomy is an academic journal published by Hindawi Publishing Corporation. The journal publishes majorly in the area(s): Galaxy & Dark matter. It has an ISSN identifier of 1687-7969. It is also open access. Over the lifetime, 365 publications have been published receiving 8178 citations.

The Core-Cusp Problem

Abstract: This paper gives an overview of the attempts to determine the distribution of dark matter in low surface brightness disk and gas-rich dwarf galaxies, both through observations and computer simulations. Observations seem to indicate an approximately constant dark matter density in the inner parts of galaxies, while cosmological computer simulations indicate a steep power-law-like behaviour. This difference has become known as the “core/cusp problem,” and it remains one of the unsolved problems in small-scale cosmology.

Primordial Non-Gaussianities from Inflation Models

Abstract: This is a pedagogical review on primordial non-Gaussianities from inflation models. We introduce formalisms and techniques that are used to compute such quantities. We review different mechanisms which can generate observable large non-Gaussianities during inflation, and distinctive signatures they leave on the non-Gaussian profiles. They are potentially powerful probes to the dynamics of inflation. We also provide a nontechnical and qualitative summary of the main results and underlying physics.

Large-Angle Anomalies in the CMB

Abstract: We review the recently found large-scale anomalies in the maps of temperature anisotropies in the cosmic microwave background. These include alignments of the largest modes of CMB anisotropy with each other and with geometry and direction of motion of the solar ssystem, and the unusually low power at these largest scales. We discuss these findings in relation to expectation from standard inflationary cosmology, their statistical significance, the tools to study them, and the various attempts to explain them.

The Solar Cycle

Abstract: Deenition The term solar cycle refers to a quasi-periodic variation with a period of about 11 years, visible in many of the Sun's observables. The solar cycle is most easily observed in indices directly related to the Sun's magnetic eld, such as sunspots. During the last decades, solar-cycle variations have also been found in many other aspects of the Sun (irradiance, surface ows, coronal shape, oscillation frequencies, etc). The modulation amplitudes may vary widely between diierent indices. It is minute in visible light, and this explains why the solar cycle is not visible to a casual naked-eye observer. Elsewhere (in the far ultraviolet, X-rays, radio frequencies) the modulation amplitude is large (Table 1). The prime cause of the solar cycle is a quasi-periodic oscillation of the solar magnetic field. Magnetic-eld indices The oldest and best known index of the solar cycle is provided by sunspots, whose discovery for Europe around 1610 is associated with the names of Fabricius, Galileo and Scheiner. The commonest sunspot index is the Z urich sunspot number R = K(10g + f), where g is the number of sunspot groups, f is the number of individual spots and K is a coeecient that corrects for diierences in the quality of the observations. Usually one derives an annual average R, shown in Fig. 1. The most striking feature of the sunspot record is the Schwabe cycle of about 11 years, discovered by Hein-rich Samuel Schwabe in 1843. By convention, the cycle that began in 1755 is assigned number 1; hence cycle 23 began in 1997. Cycle shape. A typical sunspot cycle in Fig. 1 is characterized by a sharp rise from minimum to maximum, lasting 3-6 years (on average 4.8). The duration of the rise phase is anticorrelated with the height of the maximum (Waldmeier's rule). The maximum is followed by a gradual decline lasting 5-8 years (on average 6.2). Whereas the maxima of the Z urich number are typically well-deened, this is not the case for some other solar activity indices. For example, it has been suggested that the number of large sunspots has a double-peaked maximum. Most indices vary roughly in phase with the sunspot number, and therefore the sunspot extrema are also referred to as the solar minimum and the solar maximum. On the other hand, some coronal indices are clearly out of phase with the sunspot cycle, and they peak at the sunspot …

The Observer's Guide to the Gamma-Ray Burst-Supernova Connection

Abstract: We present a detailed report of the connection between long-duration gamma-ray bursts (GRBs) and their accompanying supernovae (SNe). The discussion presented here places emphasis on how observations, and the modelling of observations, have constrained what we know about GRB-SNe. We discuss their photometric and spectroscopic properties, their role as cosmological probes, including their measured luminosity–decline relationships, and how they can be used to measure the Hubble constant. We present a statistical summary of their bolometric properties and use this to determine the properties of the “average” GRB-SN. We discuss their geometry and consider the various physical processes that are thought to power the luminosity of GRB-SNe and whether differences exist between GRB-SNe and the SNe associated with ultra-long-duration GRBs. We discuss how observations of their environments further constrain the physical properties of their progenitor stars and give a brief overview of the current theoretical paradigms of their central engines. We then present an overview of the radioactively powered transients that have been photometrically associated with short-duration GRBs, and we conclude by discussing what additional research is needed to further our understanding of GRB-SNe, in particular the role of binary-formation channels and the connection of GRB-SNe with superluminous SNe.