Dark Matter in the Milky Way

Abstract

We review most dynamical constraints on the gravitational field of spiral galaxies in general, and of the Milky Way in particular. Such constraints are of prime importance for determining the charateristics of the putative dark matter haloes of galaxies. For the Milky Way, we review observational constraints in the inner parts (cored or cusped dark matter distribution, maximum disk or not), in the solar neighbourhood (local dark matter density) and in the outer parts (virial mass and triaxial shape of the dark matter halo). We also point out various caveats, systematic effects, and large current uncertainties. Many fundamental parameters such as the local circular velocity are poorly known, evidence for triaxiality of the dark halo is shaky, and different estimates of the virial mass as well as of the local dark matter density vary by at least a factor of two. We however argue that the current best-fit value for the local dark matter density, which should be used as a benchmark for direct dark matter detection searches, is of the order of 0.5 GeV cm −3 . We also explain why alternatives to particle dark matter on galactic scales should still be very seriously considered.

Is it possible to discover a dark matter particle with an accelerator?

“…One should absolutely agree with the authors of [2], that "... the goal is to detect the particles that constitute the massive halo of dark matter that surrounds the Milky Way, as they pass through our detectors ..." Another argument is [6] that "... until dark matter particles are detected in the laboratory, it is also healthy to remember that there are hints that the dark sector might be more complicated ..." Perhaps unconsciously, the decisive role of the laboratory direct DM detection experiments was stressed here.…”

“…Dark matter particles are stable, neutral, with a clear galaxy feature Galactic Dark Matter (DM) particles do not emit or reflect any detectable electromagnetic radiation and clearly manifest themselves today only gravitationally by affecting other astrophysical objects. Numerous observational indications at astronomical and cosmological scales [1,2,3,4,5,6,7,8,9,10,11], as well as results from very sophisticated numerical many-body simulations of genesis of cosmic large-and small-scale structures (see, for example, [12]), indicate the presence of this new form of matter in the Universe.…”

“…For further consideration the local density (nearby the solar system) and local distribution of the relic DM-particle population are both very important [15]. To allow a measurable direct detection event rate in a modern DM-detector it must be not very low [6,7,10]. According to estimates based on a detailed model of our Galaxy [16] the local density of DM amounts to about ρ DM local 0.3 GeV/cm 3 5 • 10 −25 g/cm 3 .…”

“…According to estimates based on a detailed model of our Galaxy [16] the local density of DM amounts to about ρ DM local 0.3 GeV/cm 3 5 • 10 −25 g/cm 3 . Recent studies argue that the current best-fit value for the local DM density, which should be used as a benchmark for direct DM detection searches, is 0.4-0.5 GeV/cm 3 [6,17]. The local flux of DM particles, which can cross the Earth, is expected to be Φ DM local 10 5 100 GeV m DM cm −2 s −1 , where m DM is the DM particle mass.…”

A direct dark matter detection experiment is inevitable

“…Dark Matter (DM) particles do not emit or reflect any detectable electromagnetic radiation and clearly manifest themselves today only gravitationally by affecting other astrophysical objects. Numerous observational indications at astronomical and cosmological scales [3,4,5,6,7,8,9,10,11,12,13], as well as results from very sophisticated numerical many-body simulations of the genesis of cosmic large-and small-scale structures (see, for example, [14]), indicate the presence of this new form of matter in the Universe.…”