Related papers: Dark Matter in Many Forms
Dark matter, proposed decades ago as a speculative component of the universe, is now known to be the vital ingredient in the cosmos, eight times more abundant than ordinary matter, one quarter of the total energy density and the component…
Dark matter constitutes about $23\%$ of the total energy density of the universe but its properties are still little known besides that it should be composed by cold and weakly interacting particles. Many beyond standard model theories can…
Dark matter is a fundamental constituent of the universe, which is needed to explain a wide variety of astrophysical and cosmological observations. Although the existence of dark matter was first postulated nearly a century ago and its…
Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% +/- 1% baryons; 29% +/- 4% cold dark matter;…
From astronomical observations, we know that dark matter exists, makes up 23% of the mass budget of the Universe, clusters strongly to form the load-bearing frame of structure for galaxy formation, and hardly interacts with ordinary matter…
Observations in the optical, in X-rays, and gravitational lensing of galaxies, clusters of galaxies, and large-scale structure are beginning to provide clues to the dark matter problem. I review the impact of these observations on some of…
How much dark matter is there in the universe and where is it located? These are two of the most fundamental questions in cosmology. We use in this paper optical and x-ray mass determinations of galaxies, groups, and clusters of galaxies to…
It is now widely accepted that most of mass--energy in the universe is unobserved except by its gravitational effects. Baryons make only about 4% of the total, with "dark matter" making up about 23% and the "dark energy" responsible for the…
About 80 percent of the matter content of the universe is dark matter. However, the particle origin of dark matter is yet to be established. Many extensions of the Standard Model (SM) contain candidates of dark matter. The search for the…
Over the past few decades, a consensus picture has emerged in which roughly a quarter of the universe consists of dark matter. I begin with a review of the observational evidence for the existence of dark matter: rotation curves of…
A short story of dark matter as an example of a scientific revolution is given. The characteristics of stellar populations are compared with those of dark halos. The mean mass-to-luminosity ratio of stellar populations is found to be 4 in…
About one-fourth of the universe is thought to consist of dark matter. Yet there is no clear understanding about the nature of these particles. Commonly discussed dark matter candidates includes the so called WIMPs or weakly interacting…
The nature of dark matter (DM) and dark energy (DE) which is supposed to constitute about 95% of the energy density of the universe is still a mystery. There is no shortage of ideas regarding the nature of both. While some candidates for DM…
The entropies of the known entities in the universe add to a total which is some twenty orders of magnitude below the holographic limit. Based on an assumption that the entropies should saturate the limit, we suggest that there exists dark…
After two decades of efforts to identify the enigmatic dark matter that comprises the dominant form of matter in our galaxy, the mass range for viable candidates appears to have been reduced by more than 50 orders of magnitude. Positive…
The universe is composed of ordinary matter (for example, stars, planets, ourselves), dark matter and dark energy. The estimated percentage of dark matter is about $27\%$ of the entire universe, while $5\%$ is ordinary matter and the…
Astronomical and cosmological observations of the past 80 years build solid evidence that atomic matter makes up only a small fraction of the matter in the universe. The dominant fraction does not interact with electromagnetic radiation,…
We propose that dark matter consists of collections of atoms encapsulated inside pieces of an alternative vacuum, in which the Higgs field vacuum expectation value is appreciably smaller than in the usual vacuum. The alternative vacuum is…
There is strong evidence for a large fraction of dark matter in the Universe. Some of the evidence and candidates for dark matter are reviewed. Dark matter in spiral galaxies may be in the form of cold dense clouds of molecular hydrogen.…
Most of the mass density in the Universe---and in the halo of our own galaxy---exists in the form of dark matter. Overall, the contribution of luminous matter (in stars) to the mass density of the Universe is less than 1\%; primordial…