Podcasts about Cold dark matter

In the first half of the last Century, scientists realised that there must be more to space than meets the eye: without some invisible force hanging on to them, clusters of stars rotating around galaxies ought to be being flung out into space like children letting go on a playground roundabout. That force, they knew, must be gravity, but its origin - where it was coming from - no one knew.A popular theory at the time was that millions of small stars we couldn't see were lending their mass to the equation, but by carefully logging what was out there in our own Milky Way Galaxy, Gerry Gilmore... Like this podcast? Please help us by supporting the Naked Scientists

Did JWST discover dark stars? Neil deGrasse Tyson and comedian Chuck Nice explore the dark universe and how learning about dark matter could help uncover the mystery of JWST's primordial objects with theoretical physicist Katherine Freese.NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free here: https://startalkmedia.com/show/uncovering-dark-matter-mysteries-with-katherine-freese/Thanks to our Patrons Shara McAlister, Foohawt, Donna Palmieri, Trooj, Leroy Gutierrez, Tricia Livingston, Christina, Chris Ocampo, Eric Stellpflug, and John Potanos for supporting us this week.

Das Lambda-CDM-Modell beschreibt wie sich das gesamte Universum vom Urknall bis heute entwickelt hat. Es ist eigentlich erstaunlich, dass es so eine Theorie gibt, aber es gibt sie und was sie aussagt, erfahrt ihr in der neuen Folge der Sternengeschichten. Wer den Podcast finanziell unterstützen möchte, kann das hier tun: Mit PayPal (https://www.paypal.me/florianfreistetter), Patreon (https://www.patreon.com/sternengeschichten) oder Steady (https://steadyhq.com/sternengeschichten)

IWDM: The fate of an interacting non-cold dark matter - vacuum scenario by Supriya Pan et al. on Tuesday 22 November In almost every cosmological models, the equation of state of the dark matter is assumed to be zero (i.e. a pressure-less/cold dark matter). Although such hypothesis is motivated by the abundance of cold dark matter in the universe, there is however no compelling reason to set the dark matter equation of state to zero, rather, the more generic picture is to consider a free-to-vary dark matter equation of state and let the observational data decide its fate. With the growing sensitivity of the experimental data, we choose the second possibility and consider an interacting non-cold dark matter $-$ vacuum scenario in which the dark matter equation of state is constant but free-to-vary in an interval. Considering a very well known and most used interaction function in the literature, we constrain this scenario using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the legacy Planck release, baryon acoustic oscillations distance measurements and the Pantheon catalogue from Supernovae Type Ia. We find that for all the observational data sets, a non-zero value of the dark matter equation of state is preferred at 68% CL which indicates that a non-cold dark matter sector in the universe should be investigated further in order to understand the intrinsic nature of the dark matter sector. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11047v1

IWDM: The fate of an interacting non-cold dark matter - vacuum scenario by Supriya Pan et al. on Monday 21 November In almost every cosmological models, the equation of state of the dark matter is assumed to be zero (i.e. a pressure-less/cold dark matter). Although such hypothesis is motivated by the abundance of cold dark matter in the universe, there is however no compelling reason to set the dark matter equation of state to zero, rather, the more generic picture is to consider a free-to-vary dark matter equation of state and let the observational data decide its fate. With the growing sensitivity of the experimental data, we choose the second possibility and consider an interacting non-cold dark matter $-$ vacuum scenario in which the dark matter equation of state is constant but free-to-vary in an interval. Considering a very well known and most used interaction function in the literature, we constrain this scenario using the Cosmic Microwave Background (CMB) anisotropies and the CMB lensing reconstruction from the legacy Planck release, baryon acoustic oscillations distance measurements and the Pantheon catalogue from Supernovae Type Ia. We find that for all the observational data sets, a non-zero value of the dark matter equation of state is preferred at 68% CL which indicates that a non-cold dark matter sector in the universe should be investigated further in order to understand the intrinsic nature of the dark matter sector. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.11047v1

Tidal Tracks and Artificial Disruption of Cold Dark Matter Halos by Andrew J. Benson et al. on Sunday 25 September We describe a simple extension to existing models for the tidal heating of dark matter subhalos which takes into account second order terms in the impulse approximation for tidal heating. We show that this revised model can accurately match the tidal tracks along which subhalos evolve as measured in high-resolution N-body simulations. We further demonstrate that, when a constant density core is introduced into a subhalo, this model is able to quantitatively reproduce the evolution and artificial disruption of N-body subhalos arising from finite resolution effects. Combining these results we confirm prior work indicating that artificial disruption in N-body simulations can result in a factor two underestimate of the subhalo mass function in the inner regions of host halos, and a 10--20% reduction over the entire virial volume. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2206.01842v2

Tidal Tracks and Artificial Disruption of Cold Dark Matter Halos by Andrew J. Benson et al. on Sunday 25 September We describe a simple extension to existing models for the tidal heating of dark matter subhalos which takes into account second order terms in the impulse approximation for tidal heating. We show that this revised model can accurately match the tidal tracks along which subhalos evolve as measured in high-resolution N-body simulations. We further demonstrate that, when a constant density core is introduced into a subhalo, this model is able to quantitatively reproduce the evolution and artificial disruption of N-body subhalos arising from finite resolution effects. Combining these results we confirm prior work indicating that artificial disruption in N-body simulations can result in a factor two underestimate of the subhalo mass function in the inner regions of host halos, and a 10--20% reduction over the entire virial volume. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2206.01842v2

The phenomenology of the external field effect in cold dark matter models by Aseem Paranjape et al. on Tuesday 20 September In general relativity (GR), the internal dynamics of a self-gravitating system under free-fall in an external gravitational field should not depend on the external field strength. Recent work has claimed a statistical detection of an `external field effect' (EFE) using galaxy rotation curve data. We show that large uncertainties in rotation curve analyses and inaccuracies in published simulation-based external field estimates compromise the significance of the claimed EFE detection. We further show analytically that a qualitatively similar statistical signal is, in fact, expected in a $Lambda$-cold dark matter ($Lambda$CDM) universe without any violation of the strong equivalence principle. Rather, such a signal arises simply because of the inherent correlations between galaxy clustering strength and intrinsic galaxy properties. We explicitly demonstrate the effect in a baryonified mock catalog of a $Lambda$CDM universe. Although the detection of an EFE-like signal is not, by itself, evidence for physics beyond GR, our work shows that the $textit{sign}$ of the EFE-like correlation between the external field strength and the shape of the radial acceleration relation can be used to probe new physics: e.g., in MOND, the predicted sign is opposite to that in our $Lambda$CDM mocks. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2112.00026v2

Now time to find out more about the audio described tour of the Cornelia Parker exhibition at Tate Britain in London on Friday 24 June 2022 at 5.30pm lead by visually impaired artist Sally Booth. Cornelia Parker is one of Britain's best loved and most acclaimed contemporary artists. Always driven by curiosity, she reconfigures domestic objects to question our relationship with the world. Using transformation, playfulness and storytelling, she engages with important issues of our time, be it violence, ecology or human rights.  The exhibition of her work at Tate Britain brings together such iconic suspended works as Thirty Pieces of Silver 1988–9 and Cold Dark Matter: An Exploded View 1991; the immersive War Room 2015 and Magna Carta 2015, her monumental collective embroidery, as well as her films and a wealth of her innovative drawings, prints and photographs. Some works will spill out beyond the confines of the exhibition and infiltrate the permanent collection, in dialogue with the historical works they reference. RNIB Connect Radio's Toby Davey was joined by Nathan Ladd one of the Curators of the Cornelia Parker exhibition at Tate Britain to find out more about Cornelia and some of her iconic pieces that are on display in the exhibition at Tate Britain including Thirty Pieces of Silver, Cold Dark Matter and Nathan's must see work War Room. The Cornelia Parker exhibition continues at Tate Britain until 16 October 2022 and for more about the audio described tour on Friday 24 June 2022 at 5.30pm plus other accessible events and resources for blind and partially sighted people at Tate Britain do email hello@tate.org.uk or visit the Tate website - https://www.tate.org.uk/tatebritain (Image shows RNIB logo. 'RNIB' written in black capital letters over a white background and underlined with a bold pink line, with the words 'See differently' underneath)

It's a very NSFW one, pals! And also, it's got VALENCE S1E11 spoilers, so make sure you listen to that first! In this episode, I talk to Josh Rubino (Liam) and John Westover (Nico) about conveying "fuck energy." But also, we talk about modern art, control issues, and how people convey their trauma. Check out Cornelia Parker's "Mass (Colder Darker Matter)," the art piece discussed in this episode, here: The Phoenix Art Museum: https://phxart.org/arts/mass-colder-darker-matter-monton-materia-mas-oscura-mas-fria/ A video on another Cornelia Parker piece, just "Cold Dark Matter": https://www.youtube.com/watch?v=NrTvMxPl3xA&t=35s About Scoring Magic Scoring Magic is presented by Hug House Productions. You can support us for behind-the-scenes details and early previews of upcoming projects on Patreon. Support Scoring Magic by donating to the tip jar: https://tips.pinecast.com/jar/scoring-magic

Learn about why your biases are so strong, you’d choose them over making money; a new theory that “dark fluid” might mean that dark matter and dark energy are the same weird substance; and Oymyakon, one of the coldest places on Earth where people continuously live. In this podcast, Cody Gough and Ashley Hamer discuss the following stories from Curiosity.com to help you get smarter and learn something new in just a few minutes: You'd Choose Your Biases Over Making Money — https://curiosity.im/2LxPldv A New Theory Says Dark Energy and Dark Matter Might Be the Same Weird Substance — https://curiosity.im/2Lr1ocf Oymyakon Is One of the Coldest Places on Earth, But People Live There — https://curiosity.im/2LsXuQe If you love our show and you're interested in hearing full-length interviews, then please consider supporting us on Patreon. You'll get exclusive episodes and access to our archives as soon as you become a Patron! https://www.patreon.com/curiositydotcom Download the FREE 5-star Curiosity app for Android and iOS at https://curiosity.im/podcast-app. And Amazon smart speaker users: you can listen to our podcast as part of your Amazon Alexa Flash Briefing — just click “enable” here: https://curiosity.im/podcast-flash-briefing.

Professor Carlos Frenk is a cosmologist and one of the originators of the Cold Dark Matter theory for the formation of galaxies and the structure of the universe. He has worked at Durham University since 1985, where he was appointed the inaugural Ogden Professor of Fundamental Physics in 2001 and has been Director of the Institute for Computational Cosmology since 2002. Born in Mexico in 1951, he is the son of a German Jewish immigrant father and a Mexican mother with Spanish roots. After completing his physics degree in Mexico, he came to Cambridge University in the mid-1970s to do a PhD in Astronomy. His first postgraduate job took him to the University of California where he worked on a computer simulation of the universe with three fellow cosmologists, disproving the idea that the universe contains hot dark matter and establishing the theory of cold dark matter instead.Professor Frenk's papers have received more than 100,000 citations, making him one of the most frequently cited authors in the field of space science and astronomy. He has won a number of prizes for his work, including the Gold Medal of the Royal Astronomical Society. He was awarded a CBE in 2017.Presenter: Kirsty Young Producer: Cathy Drysdale.

Professor Carlos Frenk is a cosmologist and one of the originators of the Cold Dark Matter theory for the formation of galaxies and the structure of the universe. He has worked at Durham University since 1985, where he was appointed the inaugural Ogden Professor of Fundamental Physics in 2001 and has been Director of the Institute for Computational Cosmology since 2002. Born in Mexico in 1951, he is the son of a German Jewish immigrant father and a Mexican mother with Spanish roots. After completing his physics degree in Mexico, he came to Cambridge University in the mid-1970s to do a PhD in Astronomy. His first postgraduate job took him to the University of California where he worked on a computer simulation of the universe with three fellow cosmologists, disproving the idea that the universe contains hot dark matter and establishing the theory of cold dark matter instead. Professor Frenk's papers have received more than 100,000 citations, making him one of the most frequently cited authors in the field of space science and astronomy. He has won a number of prizes for his work, including the Gold Medal of the Royal Astronomical Society. He was awarded a CBE in 2017. Presenter: Kirsty Young Producer: Cathy Drysdale.

The introduction of a so-called dark sector in cosmology resolved many inconsistencies between cosmological theory and observation, but it also triggered many new questions. Dark Matter (DM) explained gravitational effects beyond what is accounted for by observed luminous matter and Dark Energy (DE) accounted for the observed accelerated expansion of the universe. The most sought after discoveries in the field would give insight into the nature of these dark components. Dark Matter is considered to be the better established of the two, but the understanding of its nature may still lay far in the future. This thesis is concerned with explaining and eliminating the discrepancies between the current theoretical model, the standard model of cosmology, containing the cosmological constant Λ as the driver of accelerated expansion and Cold Dark Matter (CDM) as main source of gravitational effects, and available observational evidence pertaining to the dark sector. In particular, we focus on the small, galaxy-sized scales and below, where N-body simulations of cosmological structure in the ΛCDM universe predict much more structure and therefore much more power in the matter power spectrum than what is found by a range of different observations. This discrepancy in small scale power manifests itself for example through the well known "dwarf-galaxy problem'" (e.g. Klypin, 1999), the density profiles and concentrations of individual haloes (Donato, 2009) as well as the properties of voids (Tikhonov, 2009). A physical process that would suppress the fluctuations in the dark matter density field might be able to account for these discrepancies. Free-streaming dark matter particles dampen the overdensities on small scales of the initial linear matter density field. This corresponds to a suppression of power in the linear matter power spectrum and can be modeled relatively straightforwardly for an early decoupled thermal relic dark matter particle. Such a particle would be neutrino-like, but heavier; an example being the gravitino in the scenario, where it is the Lightest Supersymmetric Particle and it decouples much before neutrinos, but while still relativistic. Such a particle is not classified as Hot Dark Matter, like neutrinos, because it only affects small scales as opposed to causing a suppression at all scales. However, its free-streaming prevents the smallest structures from gravitationally collapsing and does therefore not correspond to Cold Dark Matter. The effect of this Warm Dark Matter (WDM) may be observable in the statistical properties of cosmological Large Scale Structure. The suppression of the linear matter density field at high redshifts in the WDM scenario can be calculated by solving the Boltzmann equations. A fit to the resulting linear matter power spectrum, which describes the statistical properties of this density field in the simple thermal relic scenario is provided by Viel (2004). This linear matter power spectrum must then be corrected for late-time non-linear collapse. This is rather difficult already in the standard cosmological scenario, because exact solutions the the evolution of the perturbed density field in the nonlinear regime cannot be found. The widely used approaches are to the 'halofit' method of Smith (2002), which is essentially a physically motivated fit to the results of numerical simulations or using the even more physical, but slightly less accurate halo model. However, both of these non-linear methods were developed assuming only CDM and are therefore not necessarily appropriate for the WDM case. In this thesis, we modify the halo model (see also Smith, 2011) in order to better accommodate the effects of the smoothed WDM density field. Firstly, we treat the dark matter density field as made up of two components: a smooth, linear component and a non-linear component, both with power at all scales. Secondly, we introduce a cut-off mass scale, below which no haloes are found. Thirdly, we suppress the mass function also above the cut-off scale and finally, we suppress the centres of halo density profiles by convolving them with a Gaussian function, whose width depends on the WDM relic thermal velocity. The latter effect is shown to not be significant in the WDM scenario for the calculation of the non-linear matter power spectrum at the scales relevant to the present and near future capabilities of astronomical surveys in particular the Euclid weak lensing survey. In order to determine the validity of the different non-linear WDM models, we run cosmological simulations with WDM (see also Viel, 2012) using the cutting edge Lagrangian code Gadget-2 (Springel, 2005). We provide a fitting function that can be easily applied to approximate the non-linear WDM power spectrum at redshifts z = 0.5 - 3.0 at a range of scales relevant to the weak lensing power spectrum. We examine the simple thermal relic scenario for different WDM masses and check our results against resolution issues by varying the size and number of simulation particles. We finally briefly discuss the possibility that the effects of WDM on the matter power spectrum might resemble the analogous, but weaker and larger scale effects of the free-streaming of massive neutrinos. We consider this with the goal of re-examining the Sloan Digital Sky Survey data (as in Thomas, 2010). We find that the effects of the neutrinos might just differ enough from the effects of WDM to prevent the degeneracy of the relevant parameters, namely the sum of neutrino masses and the mass of the WDM particle.

Are the foundations of Dark Matter crumbling? How can a planet be blacker than black paint? What are the sunsets like on a planet with 2 suns? In this month's Naked Astronomy, we'll discover Kepler-16b; a planet with two suns, we look to recent experimental results to see if the Cold Dark Matter theory still stands, and we explore the least reflective planet ever found... Like this podcast? Please help us by supporting the Naked Scientists

Are the foundations of Dark Matter crumbling? How can a planet be blacker than black paint? What are the sunsets like on a planet with 2 suns? In this month's Naked Astronomy, we'll discover Kepler-16b; a planet with two suns, we look to recent experimental results to see if the Cold Dark Matter theory still stands, and we explore the least reflective planet ever found... Like this podcast? Please help us by supporting the Naked Scientists

Currently favoured cosmological models for structure formation of the Universe assume that a large fraction of the mass of the Universe is 'dark'. The evidence for dark matter comes from observations of its gravitational influence. Examples such as the flatness of rotation curves of spiral galaxies or the large velocities of galaxies in galaxy clusters are thought to be manifestations of its presence. Gravitational lensing can now also be used to map the dark matter distribution of the Universe. Despite the fact that the evidence for dark matter has existed for more than 75 years, it is still not clear what dark matter is made of. Particle physics provides some interesting and well-motivated candidates, but the elusive dark matter particles have not yet been detected. Therefore, the hunt for dark matter is one of the major joint efforts of cosmology and particle physics. The only way to prove the dark matter hypothesis is the direct detection of dark matter particles in a laboratory. Experiments exploit various techniques to detect dark matter particles. All of these experiments require as input the phase-space distribution of dark matter. This means they require information on the configuration-space and velocity-space distributions. These insights can only come from cosmology and the theory of structure formation in the Universe. The goal of this thesis is to predict the expected dark matter phase-space distribution near the solar system and in the dark matter halo of the Milky Way. A large part of this thesis is dedicated to a detailed analysis of the coarse-grained dark matter distribution near the Sun based on the Aquarius project, the currently largest set of Milky Way-like dark matter halo simulations. Based on these simulations we predict the local dark matter density distribution to be remarkably smooth: the density at the Sun differs from the mean over a best-fit ellipsoidal equidensity contour by less than 15% at the 99.9% confidence level. The local velocity distribution is also very smooth, but it differs systematically from a (multivariate) Gaussian distribution. This is not due to the presence of individual clumps or streams, but to broad features in the velocity modulus and energy distributions that are stable both in space and time and reflect the detailed assembly history of each halo. These features have a significant impact on the signals predicted for WIMP (weakly interacting massive particle) and axion searches. For example, WIMP recoil rates can deviate by ~10% from those expected from the best-fit multivariate Gaussian models. The axion spectra in the simulations typically peak at lower frequencies than in the case of multivariate Gaussian velocity distributions. Also in this case, the spectra show significant imprints of the formation of the halo. This implies that once direct dark matter detection has become routine, features in the detector signal will allow the study of the dark matter assembly history of the Milky Way. A new field, 'dark matter astronomy', will then emerge. The main part of this thesis focuses on the fine-grained phase-space structure of the dark matter distribution near the Sun. A new and completely general technique for calculating the fine-grained phase-space structure of dark matter throughout the Galactic halo is presented. Its goal is to understand dark matter structure on the scales relevant for direct and indirect detection experiments. The method is based on evaluating the geodesic deviation equation along the trajectories of individual dark matter simulation particles. It requires no assumptions about the symmetry or stationarity of the halo formation process. General static potentials that exhibit more complex behaviour than the separable potentials studied previously are discussed. For ellipsoidal logarithmic potentials with a core, phase mixing is sensitive to the resonance structure, as indicated by the number of independent orbital frequencies. Regions of chaotic mixing can be identified by the very rapid decrease in the configuration-space density of the associated dark matter streams. A relevant analysis is made on the evolution of the stream density in ellipsoidal NFW haloes with radially varying isopotential shape, showing that if such a model is applied to the Galactic halo, at least $10^5$ streams are expected near the Sun. The most novel aspect of the new approach is that general non-static systems can be studied through its implementation in cosmological N-body codes. The new scheme is embedded in a current state-of-the-art N-body code. Tests demonstrating that N-body discreteness effects can be kept under control in realistic configurations are presented. The new method also allows an analysis of caustics in the dark matter distribution and a detailed calculation of the annihilation radiation associated with them. Caustics are a generic feature of the nonlinear growth of structure in the dark matter distribution. If the dark matter were absolutely cold, its mass density would diverge at caustics, and the integrated annihilation probability would also diverge for individual particles participating in them. For realistic dark matter candidates, this behaviour is regularised by small but non-zero initial thermal velocities. A mathematical treatment of evolution from hot, warm or cold dark matter initial conditions is given. This scheme can be directly implemented in cosmological N-body codes. It allows the identification of caustics and the estimation of their annihilation radiation in fully general simulations of structure formation. The methods developed for the fine-grained phase-space and caustic analysis are applied to the growth of isolated dark matter haloes from self-similar and spherically symmetric initial conditions. A modified N-body code integrates the geodesic deviation equation in order to track the streams and caustics associated with individual simulation particles. The radial orbit instability causes the haloes to develop major-to-minor axis ratios approaching 10 to 1 in their inner regions. They grow similarly in time and have similar density profiles to the spherical similarity solution, but their detailed structure is very different. The higher dimensionality of the orbits causes their stream and caustic densities to drop much more rapidly than in the similarity solution. This results in a corresponding increase in the number of streams at each point. At 1% of the turnaround radius (corresponding roughly to the Sun's position in the Milky Way) we find of order 10^6 streams in our simulations, as compared to 10^2 in the similarity solution. The number of caustics in the inner halo increases by a factor of several, because a typical orbit has six turning points rather than one, but caustic densities drop by a much larger factor. This reduces the caustic contribution to the annihilation radiation. For the region between 1% and 50% of the turnaround radius, this is 4% of the total in our simulated haloes, as compared to 6.5% in the similarity solution. Caustics contribute much less at smaller radii. These numbers assume a 100GeV/c^2 neutralino with present-day velocity dispersion 0.03cm/s, but reducing the dispersion by ten orders of magnitude only doubles the caustic luminosity. Therefore, caustics will be unobservable in the inner parts of haloes. Only the outermost caustic might potentially be detectable. Finally, we present results on the fine-grained phase-space structure of cold dark matter haloes growing in the concordance LCDM cosmology. We use the geodesic deviation technique to follow the local phase-space evolution of individual simulation particles, and we apply this method to three different resolutions of the Aq-A halo of the Aquarius project. We use a fixed softening length and only change the number of particles. Good convergence is achieved for all fine-grained properties of the halo: caustic passages, stream densities, number of streams and intra-stream annihilation radiation. At the virial radius we expect about 10^7 streams. We find caustic densities to be subdominant within the virial radius: at the virial radius the maximum caustic density is comparable to the mean halo density, whereas at 10% of the virial radius the caustic density is already a factor 10^6 smaller than the mean density. We attribute this to the very efficient phase-space mixing. The contribution of caustics to the annihilation radiation at the turnaround radius is about 10%, but well below 0.1% at 10% of the virial radius.

In this episode, Scientific American editor George Musser talks with Caltech Astronomer Josh Simon about dark matter, and about the efforts to try to locate the so-called missing satellites of the Milky Way--small galaxies that have yet to be found in the numbers that the cold dark matter theory predicts. Plus we'll test your knowledge of some recent science in the news. Websites mentioned on this episode include: tinyurl.com/27g9op; www.astro.caltech.edu/~jsimon

Galaxy formation is one of the most fascinating topics of modern cosmology. Since time immemorial, people have desired to understand the origin, motion and evolution of planets, stars and, more recently, galaxies and the Universe as a whole. Great advances in astronomy always have had impact on philosophy and redefined the self-understanding of mankind within the Universe. The first milestone on the long road of discoveries was undoubtedly the formulation of the laws of gravity and mechanics in 1687 by Newton. Einstein's extension of these laws in the years 1905 and 1913 led to a revolutionised understanding of space and time. In 1929 Hubble established the expanding Universe which subsequently led to the postulation of the hot Big Bang by Lemaitre (1934). Zwicky (1933) found that most of matter in the Universe is dark. The nature of this matter, interacting only through gravity and perhaps through the weak interaction, is still a mystery. Finally, Penzias and Wilson (1965) discovered the cosmic microwave background radiation, not only confirming the theory of the Big Bang, but also - as was observed later - revealing the origin of structure in the Universe. Today, cosmology and especially galaxy formation are fast paced exciting scientific fields. Surveys like the Sloan Digital Sky Survey will soon provide a catalogue of about 500 million galaxies with an unprecedent wealth of data. Deep observations with 8 or 10 m telescopes or with the Hubble Space telescope allow to observe objects in their very early evolutionary stages. In addition to this, the dramatic increase in computer power now allows us to carry out numerical experiments on galaxies and even on the large scale structure of the Universe. The latter is possible because of the extraordinary fact that as a result of microwave background observations the properties of the Universe some 300,000 years after the Big Bang are well known. As ordinary matter makes up only about ten percent of the total matter in the Universe, it can be neglected in simulations in a first approximation. An initial density field can then be evolved under the sole influence of gravity. The result of such simulations may be combined with semi-analytic models for the baryonic physics associated with galaxy formation. Gravity is a long range force, and it turns out that length scales of 100 Mpc or more have to be included in large scale structure simulations in order to obtain results that are representative for the Universe as a whole. The sizes of galaxies, however, are three to four orders of magnitude smaller than this so that numerical resolution has always been a concern in simulations which try to include galaxy formation. A clever and powerful trick alleviates this problem. After a low-resolution simulation has been performed, a small region of interest is selected and the simulation is run again, this time concentrating most of the computational effort on the small region, allowing the resolution to be increase dramatically without losing tidal influences from the large cosmological volume. This technique - called resimulation - is the driving force behind all the simulations that were performed for this thesis. After having run about 1500 supercomputer jobs it is clear that this technique is extremely powerful and allows the faithful simulation of objects that are far into the regime of non-linear evolution while taking into account the full cosmological context. In the first chapter of this work we briefly introduce aspects of the observable Universe and discuss the relevant theoretical background for this thesis. In the second chapter we use high-resolution simulations of structure formation to investigate the influence of the local environment of dark matter haloes on their properties. We run a series of four re-simulations of a typical, carefully selected representative region of the Universe so that we can explicitly check for convergence of the numerical results. In our highest resolution simulation we are able to resolve dark matter haloes as small as the one of the large Magellanic cloud. We propose a new method to estimate the density in the environment of a collapsed object and find weak correlations of the spin parameter and the concentration parameter with the local halo density. We find no such correlation for the halo shapes, the formation time and the last major merging event. In a second step we produce catalogues of model galaxies using a semi-analytic model of galaxy formation. We find correlations between the bulge-to-disk luminosity and the B-V colour index with the local environment. In chapter three we compare observations of the internal structure and kinematics of the eleven known satellites of the Milky Way with simulations of the formation of its dark halo in a LambdaCDM universe. Earlier work by Moore et al. 1999 and Klypin et al. 1999 claimed the cosmological concordance model of the Universe, the LambdaCDM model, to disagree with observations. The so-called "substructure-problem" is one of the two major challenges for this model and has attracted much attention. In order to remove the discrepancy, changes of the cosmological model have been proposed. We reinvestigate the substructure-problem using our ultra-high resolution simulations. For a galaxy-sized dark matter halo, our mass resolution is the highest resolution ever achieved. In contrast to the work of Moore et al. 1999 and Klypin et al. 1999, we find excellent agreement. The observed kinematics are exactly those predicted for stellar populations with the observed spatial structure orbiting within the most massive "satellite" substructures in our simulations. Less massive substructures have weaker potential wells than those hosting the observed satellites. If there is a halo substructure "problem", it consists in understanding why halo substructures have been so inefficient in making stars. We find that suggested modifications of dark matter properties (e.g. self-interacting or warm dark matter) may well spoil the good agreement found for standard Cold Dark Matter. If the dark matter in the Universe is made of weakly self-interacting particles, they may self-annihilate and emit gamma-rays. The detection of the gamma-ray signal would finally, after seventy years since its discovery, shed light on the nature of the dark matter. In chapter four we use our ultra-high resolution numerical simulations to estimate directly the annihilation flux from the central region of the Milky Way and from dark matter substructures in its halo. Such estimates remain uncertain because of their strong dependence on the structure of the densest regions of the halo. Our numerical experiments suggest, however, that less direct calculations have typically overestimated the emission from the centre of the Milky Way and from its halo's substructure. We find an overall enhancement of at most a factor of a few with respect to a smooth halo of standard NFW structure. For an observation outside the region around the galactic centre where the diffuse galactic gamma-ray background is dominant, GLAST can probe a large region of possible MSSM models. This result is independent of the exact structure of the innermost region of the Galaxy. Our analysis shows that the flux from the inner galaxy exceeds the expected contribution from the brightest substructure by a large factor. Nevertheless, for certain MSSM models substructure halos might be detectable with GLAST.