There is robust evidence of dark matter in our galaxy
the verdict
SUPPORTED
the evidence backs this
refutedsupported
the weight of evidence
10 sources for · 0 against
Multiple peer-reviewed cosmological studies, cosmic microwave background measurements, and galactic kinematic surveys consistently confirm the existence of dark matter and its role as a fundamental component of the universe.
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also well-motivated within high energy physics, appearing in theories related to CP -violation in the standard model, supersymmetric theories, and theories with extra-dimensions, including string theory, and so axion cosmology offers us a unique view onto these theories. I review the motivation and models for axions in particle physics and string theory. I then present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via BBN, the CMB, reionization and structure formation, up to the present-day Universe. Topics covered include: axion dark matter (DM); direct and indirect detection of axions, reviewing existing and future experiments; axions as dark radiation; axions and the cosmological constant problem; decays of heavy axions; axions and stellar astrophysics; black hole superradiance; axions and astrophysical magnetic fields; axion inflation, and axion DM as an indirect probe of inflation. A major focus is on the population of ultralight axions created via vacuum realignment, and its role as a DM candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be use
We present cosmological parameter results from the final full-mission Planck measurements of the cosmic microwave background (CMB) anisotropies, combining information from the temperature and polarization maps and the lensing reconstruction. Compared to the 2015 results, improved measurements of large-scale polarization allow the reionization optical depth to be measured with higher precision, leading to significant gains in the precision of other correlated parameters. Improved modelling of the small-scale polarization leads to more robust constraints on many parameters, with residual modelling uncertainties estimated to affect them only at the 0.5σ level. We find good consistency with the standard spatially-flat 6-parameter ΛCDM cosmology having a power-law spectrum of adiabatic scalar perturbations (denoted “base ΛCDM” in this paper), from polarization, temperature, and lensing, separately and in combination. A combined analysis gives dark matter density Ωch2 = 0.120 ± 0.001, baryon density Ωbh2 = 0.0224 ± 0.0001, scalar spectral index ns = 0.965 ± 0.004, and optical depth τ = 0.054 ± 0.007 (in this abstract we quote 68% confidence regions on measured parameters and 95% on upper limits). The angular acoustic scale is measured to 0.03% precision, with 100θ* = 1.0411 ± 0.0003. These results are only weakly dependent on the cosmological model and remain stable, with somewhat increased errors, in many commonly considered extensions. Assuming the base-ΛCDM cosmology, the inferr
(abridged) Applying the Jeans equation to eight bright dSph galaxies, we find that the enclosed mass at the half-light radius is well constrained and robust to a wide range of halo models and anisotropies. We derive a simple formula that estimates M(r_{half}) accurately with respect to a full Jeans analysis. Applying this formula to Local Group dSphs with kinematic data, we demonstrate a correlation between M(r_{half}) and r_{half}. The slope is M\propto r^{1.4\pm 0.4}, or in terms of the mean density interior to the half-light radius, \propto r^{-1.6\pm 0.4}. This relation is driven by the fact that the dSph data exhibit a correlation between global velocity dispersion and half-light radius. These empirical results are consistent with the notion that all dSphs are embedded within a 'universal' dark matter halo of fixed shape and narrow range in normalization. A cuspy 'NFW' halo with scale radius r_0 ~ 1 kpc represents one viable candidate. A cored universal halo must have scale radius $\la 200$ pc and is slightly less suitable than NFW in terms of $\chi^2$, but is not ruled out. We argue that tidal forces are unlikely to cause universality of dSph halos, but tides can affect the inferred inner shape of a universal halo. For an NFW halo or core of fixed scale radius, the velocity dispersion profiles of the brightest dSphs are consistent with a range in maximum circular velocity, V_{max} \sim 10-25 km/s. Assuming that their measured velocity dispersions accurately reflect thei
The European Space Agency’s Planck satellite, which was dedicated to studying the early Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the microwave and submillimetre sky continuously between 12 August 2009 and 23 October 2013, producing deep, high-resolution, all-sky maps in nine frequency bands from 30 to 857 GHz. This paper presents the cosmological legacy of Planck, which currently provides our strongest constraints on the parameters of the standard cosmological model and some of the tightest limits available on deviations from that model. The 6-parameter ΛCDM model continues to provide an excellent fit to the cosmic microwave background data at high and low redshift, describing the cosmological information in over a billion map pixels with just six parameters. With 18 peaks in the temperature and polarization angular power spectra constrained well, Planck measures five of the six parameters to better than 1% (simultaneously), with the best-determined parameter (θ*) now known to 0.03%. We describe the multi-component sky as seen by Planck, the success of the ΛCDM model, and the connection to lower-redshift probes of structure formation. We also give a comprehensive summary of the major changes introduced in this 2018 release. The Planck data, alone and in combination with other probes, provide stringent constraints on our models of the early Universe and the large-scale structure within which all astrophysical objects form and evolve. We di
Cosmological observations provide our most robust evidence for dark matter that is (approximately) collisionless and cold, and furthermore can provide powerful tests of the non-gravitational properties of dark matter. There are exciting prospects for significant experimental/observational progress in the coming years. In particular, current experiments are targeting a first confirmed detection of primordial 21 cm radiation and a measurement of its power spectrum, which would open a new observational window on the end of the cosmic dark ages and cosmic dawn. On a longer timescale, there are proposed missions that could improve our measurements of the energy spectrum of the cosmic microwave background radiation by 3+ orders of magnitude, providing a new physical probe of the thermal history of the universe up to keV temperatures. In this contribution, I will discuss how signals from dark matter interactions with Standard Model particles, in particular through annihilation and decay of particle-like dark matter, could appear in these observables, and recent improvements in their theoretical modeling. There are existing stringent and broadly applicable limits on annihilating and decaying dark matter (especially at sub-GeV mass scales) from the cosmic microwave background, and complementary and competitive bounds from the Lyman-α forest for leptonically decaying light dark matter. I will outline how energy injections that are not currently excluded could change the conditions of t
Despite the incredible progress made in cosmology and particle physics in the last century, there are still many unanswered questions. Specifically, we have robust evidence showing that ~85 % of the matter content of the universe is invisible and only interacts gravitationally. Furthermore, observations show neutrinos to have a non-zero mass, which is not readily explained with the Standard Model of particle physics. Moreover, as we acquire increasingly precise data on different cosmological sca
I summarize recent observations of the kinematics of hot tracers in elliptical galaxy halos (globular clusters, planetary nebulae, and integrated stellar light), and what these tell us about the dynamics, dark matter content, and formation of ellipticals. A generic result is the ubiquity of dark matter halos in ellipticals. Studies of globular clusters and planetary nebulae are now finding outer-halo rotation in many ellipticals, with V/sigma ~ 1 beyond a few R_e. In some giant ellipticals (M49, M87), there are possible kinematic differences between metal-poor and metal-rich globular clusters. These results are consistent with a merger origin for ellipticals. High-quality data and new modelling techniques now make it possible to determine simultaneously the orbital anisotropy and gravitational potential in ellipticals from integrated-light measurements; such studies now provide the best evidence for dark matter halos in ellipticals.The new generation of 8-10m telescopes, with multi-object and integral-field spectrographs, will dramatically increase sample sizes of discrete tracers and provide two-dimensional spectroscopy of elliptical halos. New methods of analysis will allow robust determinations of stellar kinematics and dark matter distributions in a much larger number of ellipticals. Comparison with numerical simulations, which are becoming ever more detailed and physically realistic, will become increasingly important.
We report the serendipitous discovery of an extended stellar halo surrounding the low-mass galaxy Ark 227 ( M _* = 5 × 10 ^9 M _⊙ ; d = 35 Mpc) in deep JWST NIRCam imaging from the Blue Jay Survey. The F200W–F444W color provides robust star–galaxy separation, enabling the identification of stars at very low density. By combining resolved stars at large galactocentric distances with diffuse emission from NIRCam and Dragonfly imaging at smaller distances, we trace the surface-brightness and color profiles of this galaxy over the entire extent of its predicted dark matter halo, from 0.1 to 100 kpc. Controlled N -body simulations have predicted that minor mergers create “accretion shelves” in the surface-brightness profile at large radius. We observe such a feature in Ark 227 at 10–20 kpc, which, according to models, could be caused by a merger with total mass ratio 1:10. The metallicity declines over this radial range, further supporting the minor merger scenario. There is tentative evidence of a second shelf at μ _V ≈ 35 mag arcsec ^−2 extending from 50 to 100 kpc, along with a corresponding drop in metallicity. The stellar mass in this outermost envelope is ≈10 ^7 M _⊙ . These results suggest that Ark 227 experienced multiple mergers with a spectrum of lower-mass galaxies—a scenario that is broadly consistent with the hierarchical growth of structure in a cold-dark-matter-dominated universe. Finally, we identify an ultra-faint dwarf associated with Ark 227 with M _* ≈ 10 ^5 M
requires only that there is some state to play the role of false vacuum, and there is some mechanism to … there must be about ten times the | amount of dark matter in what had been thought of as the void surrounding … by particle physicists to explain dark matter. Although dark matter has been inferred from its gravitational
requires only that there is some state to play the role of false vacuum, and there is some mechanism to … there must be about ten times the amount of dark matter in what had been thought of as the void surrounding … by particle physicists to explain dark matter. Although dark matter has been inferred from its gravitational
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