The Core-Cusp Problem

Dark matter is one of the main ingredients of the universe.Early optical measurements of the rotation of spiral galaxies indicated the possible presence of large amount of dark matter in their outer parts, though in many cases the rotation curve could also be explained by the stars alone .Observation at even large distance from the galaxy centers using the 21 cm line of neutral hydrogen definitively confirmed the mass discrepancy .For an extensive review see Sofue and Rubin .Most of these early observation concentrated on late-type disk galaxies which all share the property of having an almost constant rotation velocity in their outer parts  (the so-called flat rotation curve.As the dynamical contribution  of the stars and the gas is insufficient to explain the high rotation velocities in the outer parts this implies that most of the observe rotation there must be due to some other material  the dark matter.The observe constant velocity suggests that the dark matter in the outer parts of galaxies has a mass density profile closely resembling that of an isothermal sphere that is p ~ r-2

 In the inner parts pf galaxies stars are obviously presents and they must be the cause of a (possibly large) fraction of the observed rotation velocity.This therefore leads to a transition from the inner parts where the starts contribute to (and in many cases dominate) the dynamics to the outer parts where the dark matter important. 

   

Dwarf spheroidal galaxies are considered

Dwarf spheroidal galaxies are considered to provide good astronomical sites for the study of the nature of dark
matter.in kinematics of milky way satellites mass estimates, rotation limits, and proper motion,
L.Strigari reviews the evidence for the presence of dark matter in dwarf spheroidal companions
of the milky way.M. Khulen portrays prospects for the detection of the hypothetical dark matter
particle.His paper titled .The dark matter annihilation singal from
dwarf galaxies and subhalos.A. Kosowsky makes the case that 

Dwarf-Galax Cosmology

Guest Editor:Regina Schult-Ladbeck,Ulrich Hopp Elias Brinks,and Andrey kravtsov
Dwarf glaxies provide opportunities for drawing inferences
 about the processes in the early universe by observing our
 <cosmological backyard>--the Local Group and its vicinity.
This special issue of the open-access journal Advance in
Astronomy is a snapshot of the current state of the art of
dwarf-glaxy cosmology.The issue contains fourteen review
papers, and one original research artical.All papers were
peer-reviewed by a minimum of two referees.
    Dwarf galaxy continue to challenge our cosmology
models and models of glaxy formation. Two well-known
problems are the <missing satellites problem> and the cores
versus cups problem.
The dilemma posed by the fact that observation seem to indicate an
approximately constant dark matter density in the inner parts of galaxies
 when cosmological simulation prefer a step power law like behavior that
 is assessed by W. J. G. de Blok in the paper .Dark matter substructure
dwarf galactic satellites .He emphasizes and their tension with observe
tional data