Космический мусор, как следствие человеческой деятельности

В данной статье рассматриваются проблемы загрязнения космического пространства. В статьеописывается, какими опасными могут быть космические полеты, даже беспилотные спутники находятсяв постоянной опасности. Кроме того, что мы можем предпринять для устранения этих проблем, кпримеру, выведенные из строя спутники должны быть аккуратно утилизированы, их можноперенаправить на более низкую орбиту или они могут сгореть в плотных слоях атмосферы. Если непредпринять вовремя необходимые мероприятия, то они могут столкнуться с еще действующимиспутниками и вывести их из строя, а это может привести к цепной реакции. В статье описывается, какзащищены спутники от внешнего воздействия и что проблема их утилизации должна решаться еще настадии проектирования. Если мы уже на данном этапе времени займемся данной проблемой, то мысможем оставить будущим поколениям чистый и безопасный космос.Im vorliegenden Artikel werden die Probleme der Weltraumverschmutzung dargestellt. Der Artikelbeschreibt, wie gefahrlich die Weltraummissionen sein konnen, dass sogar unbemannte Satelliten der standigenGefahr ausgesetzt werden. Genauso erfahren wir, was wir gegen diese Gefahren tun konnen, z.B. ausgedienteSatelliten vorsichtig zu entsorgen,indemman sie auf eine andere Umlaufbahn bringt oder in den festen Schichten derErde vergluhen lasst. Wenn man dies nicht macht, so konnen sie mit den funktionierenden Satellitenzusammensto?en und diese au?er Betrieb setzen, was zur einen Kettenreaktion fuhren kann. Zudem beschreibt derText, wie die Satelliten geschutzt werden z.B. mit Hilfe von Schottelementen und dass man die Probleme derEntsorgung schon in der Projektierung angehen muss. Wenn wir dieses Problem schon heute angehen, souberlassen wir unserer nachfolgenden Generation einen sauberen und sicheren Weltraum

Breaking Cosmological Degeneracies in Galaxy Cluster Surveys with a Physical Model of Cluster Structure

Forthcoming large galaxy cluster surveys will yield tight constraints on cosmological models. It has been shown that in an idealized survey, containing > 10,000 clusters, statistical errors on dark energy and other cosmological parameters will be at the percent level. It has also been shown that through "self-calibration", parameters describing the mass-observable relation and cosmology can be simultaneously determined, though at a loss in accuracy by about an order of magnitude. Here we examine the utility of an alternative approach of self-calibration, in which a parametrized ab-initio physical model is used to compute cluster structure and the resulting mass-observable relations. As an example, we use a modified-entropy ("pre-heating") model of the intracluster medium, with the history and magnitude of entropy injection as unknown input parameters. Using a Fisher matrix approach, we evaluate the expected simultaneous statistical errors on cosmological and cluster model parameters. We study two types of surveys, in which a comparable number of clusters are identified either through their X-ray emission or through their integrated Sunyaev-Zel'dovich (SZ) effect. We find that compared to a phenomenological parametrization of the mass-observable relation, using our physical model yields significantly tighter constraints in both surveys, and offers substantially improved synergy when the two surveys are combined. These results suggest that parametrized physical models of cluster structure will be useful when extracting cosmological constraints from SZ and X-ray cluster surveys. (abridged)Comment: 22 pages, 8 figures, accepted to Ap

Physical approximations for the nonlinear evolution of perturbations in dark energy scenarios

The abundance and distribution of collapsed objects such as galaxy clusters will become an important tool to investigate the nature of dark energy and dark matter. Number counts of very massive objects are sensitive not only to the equation of state of dark energy, which parametrizes the smooth component of its pressure, but also to the sound speed of dark energy as well, which determines the amount of pressure in inhomogeneous and collapsed structures. Since the evolution of these structures must be followed well into the nonlinear regime, and a fully relativistic framework for this regime does not exist yet, we compare two approximate schemes: the widely used spherical collapse model, and the pseudo-Newtonian approach. We show that both approximation schemes convey identical equations for the density contrast, when the pressure perturbation of dark energy is parametrized in terms of an effective sound speed. We also make a comparison of these approximate approaches to general relativity in the linearized regime, which lends some support to the approximations.Comment: 15 pages, 2 figure

Redefining the Missing Satellites Problem

Numerical simulations of Milky-Way size Cold Dark Matter (CDM) halos predict a steeply rising mass function of small dark matter subhalos and a substructure count that greatly outnumbers the observed satellites of the Milky Way. Several proposed explanations exist, but detailed comparison between theory and observation in terms of the maximum circular velocity (Vmax) of the subhalos is hampered by the fact that Vmax for satellite halos is poorly constrained. We present comprehensive mass models for the well-known Milky Way dwarf satellites, and derive likelihood functions to show that their masses within 0.6 kpc (M_0.6) are strongly constrained by the present data. We show that the M_0.6 mass function of luminous satellite halos is flat between ~ 10^7 and 10^8 M_\odot. We use the ``Via Lactea'' N-body simulation to show that the M_0.6 mass function of CDM subhalos is steeply rising over this range. We rule out the hypothesis that the 11 well-known satellites of the Milky Way are hosted by the 11 most massive subhalos. We show that models where the brightest satellites correspond to the earliest forming subhalos or the most massive accreted objects both reproduce the observed mass function. A similar analysis with the newly-discovered dwarf satellites will further test these scenarios and provide powerful constraints on the CDM small-scale power spectrum and warm dark matter models.Comment: 8 pages, 6 figure

Substructure Boosts to Dark Matter Annihilation from Sommerfeld Enhancement

The recently introduced Sommerfeld enhancement of the dark matter annihilation cross section has important implications for the detection of dark matter annihilation in subhalos in the Galactic halo. In addition to the boost to the dark matter annihilation cross section from the high densities of these subhalos with respect to the main halo, an additional boost caused by the Sommerfeld enhancement results from the fact that they are kinematically colder than the Galactic halo. If we further believe the generic prediction of CDM that in each subhalo there is an abundance of substructure which is approximately self-similar to that of the Galactic halo, then I show that additional boosts coming from the density enhancements of these small substructures and their small velocity dispersions enhance the dark matter annihilation cross section even further. I find that very large boost factors ($10^5$ to $10^9$) are obtained in a large class of models. The implications of these boost factors for the detection of dark matter annihilation from dwarf Spheroidal galaxies in the Galactic halo are such that, generically, they outshine the background gamma-ray flux and are detectable by the Fermi Gamma-ray Space Telescope.Comment: PRD in pres