Colloquia
Talks given by high profile astronomers and scientists.
Abstract
In our now-standard picture for the growth of structure, dark matter halos are the basic unit of nonlinear structure in the present Universe. I will report results from simulations of galaxy-scale dark halos with more than an order of magnitude better mass resolution than any previously published work. Tests demonstrate detailed convergence for (sub)structures well below a millionth the mass of the final system. Even with such resolution the fraction of halo mass in bound subhalos does not rise above a few percent within the half-mass radius. I will also present a new simulation technique which allows structure in the dark matter distribution to be studied on very much smaller scales. This is required for accurate forecasts of the expected signal both in earth-bound experiments designed to detect dark matter directly, and in indirect detection experiments like GLAST which attempt to image dark matter annihilation radiation at gamma-ray wavelengths.
Abstract
Red Dwarf (dM) stars are the most numerous stars in our Galaxy. These faint, cool, long-lived, and low mass stars make up > 80% of all stars in the Universe. Determining the number of red dwarfs with planets and assessing planetary habitability (a planet’s potential to develop and sustain life) are critically important because such studies would indicate how common life is in the universe. Our program - "Living with a Red Dwarf" addresses these questions by investigating the long-term nuclear evolution and magnetic-dynamo coronal and chromospheric X-ray to Ultraviolet properties of red dwarf stars with widely different ages. The major focus of the program is to study the magnetic-dynamo generated X-ray-Ultraviolet emissions and flare properties of red dwarf stars from youth to old age. Emphasized are how the stellar X-UV emissions, flares & winds affect hosted planets and impact their habitability. We have developed age-rotation-activity relations and also are constructing irradiance tables (X-UV fluxes) that can be used to model the effects of X-UV radiation on planetary atmospheres and on possible life on nearby hosted planets. Despite the earlier pessimistic view that red dwarfs stars are not suitable for habitable planets - mainly because their low luminosities require a hosted planet to orbit quite close (r <0.3 AU) to be sufficiently warm to support life. Our initial results indicate that red dwarf stars (in particular the warmer dM stars) can indeed be suitable hosts for habitable planets capable of sustaining life for hundreds of billion years. Some examples of red dwarf stars currently known to host planets are discussed.
Abstract
Durante la segunda mitad del siglo XX la biología ha emergido de forma explosiva como una disciplina con enorme proyección de futuro con toda clase de implicaciones sociales. El origen de esta revolución fue el desciframiento en 1953 de la naturaleza de la información biológica, el ADN. La propia estructura de esta molécula explica la forma en que la información biológica está impresa y lleva implícita además el mecanismo de replicación, de forma que esta información se transmite de forma fidedigna de una generación a otra a lo largo de miles de millones de años de evolución. El estudio de la estructura, función y propiedades del ADN ha sido uno de los focos principales de atención de la Biología en los últimos 30 años, ha dado lugar a tecnologías muy poderosas de manipulación genética en diversos organismos y ha permitido desarrollar proyectos de gran calado, como el Proyecto Genoma Humano. El desarrollo de estas tecnologías es muy rápido y abre la posibilidad en un futuro no muy lejano de la modificación genética dirigida de la propia especie humana. Durante el coloquio se presentarán los hitos del conocimiento biológico que han conducido a la situación actual y se discutirán las promesas, perspectivas y problemas potenciales que ofrecerá la biología del siglo XXI.
Abstract
A continuous magnetic field evolving under the hydromagnetic frozen-in condition preserves its field topology. Depending on that field topology, the evolving field may inevitably develop electric current-sheets, i.e., magnetic tangential discontinuities, in the course of nonlinear fluid-field interaction. This inevitability obtains for all field topologies one could prescribe for the field, except those of a special subset of measure zero. This theory of Eugene Parker is based on demonstrating that a field endowed with a fixed topology cannot generally find an equilibrium state in which the field is everywhere spatially continuous. I will discuss a recent development of this magnetostatic problem from an intuitive point of view, giving a basic understanding of why current sheets not only form easily but do so throughout a magnetic field. Parker’s theory explains the heating of the solar corona, to million-degree temperatures, in terms of spontaneous current sheets that must form because of high electrical conductivity, and, yet, must dissipate in spite of that high (but finite) conductivity. This process may be the fundamental reason for the high-temperature plasmas found almost everywhere in the astrophysical universe
Upcoming talks
- TODAY: One day at DKISTAndrés ParraguezMonday March 31, 2025 - 15:00 GMT+1 (Aula)
- Latest Neutrino Achievements and Possible Synergies to Science in the IACProf. Anatael CabreraThursday April 3, 2025 - 10:30 GMT+1 (Aula)
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