Two distinct sequences of blue straggler stars in the globular cluster M30

Stars in globular clusters are generally believed to have all formed at the same time, early in the Galaxy's history. 'Blue stragglers' are stars massive enough that they should have evolved into white dwarfs long ago. Two possible mechanisms have been proposed for their formation: mass transfer between binary companions and stellar mergers resulting from direct collisions between two stars. Recently, the binary explanation was claimed to be dominant. Here we report that there are two distinct parallel sequences of blue stragglers in M30. This globular cluster is thought to have undergone 'core collapse', during which both the collision rate and the mass transfer activity in binary systems would have been enhanced. We suggest that the two observed sequences arise from the cluster core collapse, with the bluer population arising from direct stellar collisions and the redder one arising from the evolution of close binaries that are probably still experiencing an active phase of mass transfer.Comment: Published on the 24th December 2009 issue of Natur

Dynamical age differences among coeval star clusters as revealed by blue stragglers

Globular star clusters that formed at the same cosmic time may have evolved rather differently from a dynamical point of view (because that evolution depends on the internal environment) through a variety of processes that tend progressively to segregate stars more massive than the average towards the cluster centre. Therefore clusters with the same chronological age may have reached quite different stages of their dynamical history (that is, they may have different dynamical ages). Blue straggler stars have masses greater than those at the turn-off point on the main sequence and therefore must be the result of either a collision or a mass-transfer event. Because they are among the most massive and luminous objects in old clusters, they can be used as test particles with which to probe dynamical evolution. Here we report that globular clusters can be grouped into a few distinct families on the basis of the radial distribution of blue stragglers. This grouping corresponds well to an effective ranking of the dynamical stage reached by stellar systems, thereby permitting a direct measure of the cluster dynamical age purely from observed properties.Comment: Published on the 20 December 2012 issue of Natur

Time as an Illusion

We review the idea, due to Einstein, Eddington, Hoyle and Ballard, that time is a subjective label, whose primary purpose is to order events, perhaps in a higher-dimensional universe. In this approach, all moments in time exist simultaneously, but they are ordered to create the illusion of an unfolding experience by some physical mechanism. This, in the language of relativity, may be connected to a hypersurface in a world that extends beyond spacetime. Death in such a scenario may be merely a phase change

O movimento funcional de alcance em uma abordagem ecológica

Teorias de controle motor tradicionais assumiam um modelo de representação interna responsável pela organização e regulação do alcance, tendo por controlador o sistema nervoso central (SNC). Perspectivas contemporâneas questionam a habilidade de somente o SNC controlar e regular os movimentos. Ações podem não ser guiadas apenas pelo SNC, mas também por informações presentes no ambiente, estando o controle no sistema indivíduo-ambiente. A detecção da informação é um processo ativo: o indivíduo explora o ambiente, percebe possibilidades de ação fornecidas por ele e age em reposta ao que é oferecido. O objetivo deste estudo foi descrever o desenvolvimento e a coordenação do alcance em uma perspectiva teórica fundamentada na abordagem ecológica à percepção-ação, para promover melhor compreensão do movimento humano. Discutem-se nesta revisão de literatura o desenvolvimento do alcance desde a infância até a idade adulta, formas de operacionalização, fatores extrínsecos e intrínsecos relacionados, relações invariantes entre indivíduo e objeto a ser alcançado. Esse referencial teórico pode permitir a compreensão de como intervenções alteram a estabilidade vigente no sistema, levando à emergência de novas soluções funcionais. Em uma visão ecológica, o alcance é entendido de forma ampla: para explicar a ocorrência do movimento, devem considerar-se as informações do ambiente, além das características intrínsecas do indivíduo.Traditional motor control theories rely on a model of internal representation responsible for the organization and regulation of reaching movements, controlled by the central nervous system (CNS). Contemporary perspectives argue the ability of the CNS alone to control and regulate voluntary movements, since actions may also be guided by environmental information, wherein control would be exerted by the individual-environment system. The detection of information is an active process: subjects explore the environment, perceive possibilities of action, and act in response to the environment. The purpose of this study is to describe development and coordination of reaching movements from a theoretical perspective based on an ecological approach to perception-action, in order to provide better understanding of human movement. This literature review discusses the development of reaching movements from infants to adults, operational functions, related extrinsic and intrinsic factors, and invariant relations between the subject and the target object. This theoretical framework allows for a better understanding on how interventions may alter system stability, leading to the emergency of new functional solutions. In an ecological approach, reaching is understood in a broad way: in order to explain movement, environment information is considered, besides subjects' intrinsic characteristics

Contributions of Albert Einstein to Earth Sciences: A review in Commemoration of the World Year of Physics

The World Year of Physics (2005) is an international celebration to commemorate the one hundredth anniversary of Einstein's "Annus Mirabilis". The United Nations has officially declared 2005 the International Year of Physics. However, the impact of Einstein's ideas was not restricted to physics. Among numerous other disciplines, Einstein also made significant and specific contributions to Earth Sciences. His geosciences-related letters, comments, and scientific articles, are dispersed, not easily accesible and are poorly known. The present review attempts to integrate them, as a tribute to Einstein in commemoration of this centenary. These contributions can be classified into three basic areas: geodynamics, geological (planetary) catastrophism and fluvial geomorphology.Comment: 17 pages, no figures, to be published in Naturwissenschafte

The Dynamical Structure and Evolution of Giant Molecular Clouds

Giant molecular clouds (GMCs) are the sites of star formation in the Galaxy. Many of their properties can be understood in terms of a model in which the GMCs and the star-forming clumps within them are in approximate pressure equilibrium, with turbulent motions treated as a separate pressure component

Estimation of population size when capture probability depends on individual state

We develop a multi-state model to estimate the size of a closed population from capture–recapture studies. We consider the case where capture–recapture data are not of a simple binary form, but where the state of an individual is also recorded upon every capture as a discrete variable. The proposed multi-state model can be regarded as a generalisation of the commonly applied set of closed population models to a multi-state form. The model allows for heterogeneity within the capture probabilities associated with each state while also permitting individuals to move between the different discrete states. A closed-form expression for the likelihood is presented in terms of a set of sufficient statistics. The link between existing models for capture heterogeneity is established, and simulation is used to show that the estimate of population size can be biased when movement between states is not accounted for. The proposed unconditional approach is also compared to a conditional approach to assess estimation bias. The model derived in this paper is motivated by a real ecological data set on great crested newts, Triturus cristatus. Supplementary materials accompanying this paper appear online