Supermassive Black Holes

Supermassive black holes (SMBHs) represent an important aspect of galaxy evolution theory that remains at the frontier of modern research. Like their stellar-mass versions, SMBHs have Schwarzschild radii, prevent light from escaping their event horizons and form accretion disks (ADs). Understanding SMBH origin and growth is of central importance in extragalactic astron- omy due to their connection with the evolution of galaxies (Kelly et al. 2010).

Essay: Supermassive Black Holes

Migrating Planets

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Among the pioneers of the idea of swirling vortices of gas being responsible for the formation of the solar system was Descartes (1644). In his treatise, he speculated that God sent clouds adrift which changed into comets and planets. Although lacking scientific detail, parallels can be observed with nebular hypotheses pro- posed almost a century later by Swedenborg (1734) and, later, Kant (1755) using Newtonian principles. The first to develop a model of the rotating gaseous nebula collapsing and evolving into a planetary system was, however, Laplace (1796) who did it in a rigorous mathematical way. Although recent history of cosmological theories includes many contrasting alternatives (Buffon 1745; Chamberlin 1901; Jeans 1928; Jeffreys 1929; Whipple 1948), scientific consensus appears to be emerging on how the solar system evolved into its current state.

Essay: Migrating Planets

Liquid Water on Mars

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Geomorphological, mineralogical and other evidence of the conditions favoring the existence of water on Mars in liquid phase is reviewed. This includes signatures of past and, possibly, present aqueous environments, such as the northern ocean, lacustrine environments, sedimentary and thermokarst landforms, glacial activity and water erosion features. Reviewed also are hydrous weathering processes, observed on surface remotely and also via analysis of Martian meteorites. Chemistry of Martian water is discussed: the triple point, salts and brines, as well as undercooled liquid interfacial and solid-state greenhouse effect melted waters that may still be present on Mars. Current understanding of the evolution of Martian hydrosphere over geological timescales is presented from early period to the present time, along with the discussion of alternative interpretations and possibilities of dry and wet Mars extremes.

Essay: Liquid Water on Mars