The Dark Matter Of Galactic Halos

The unexplained source of the extended flat portion of rotation curves of galaxies is attributed to dark matter in the galactic halos. 1. We show it is extremely implausible that any galactic halo is made of particles. 2. We show that if halos are made of fluctuations in a simple classic scalar field, one can produce observed rotation curves. 3. If we consider a universe filled with abuting scalar field halos, we can define a new average cosmological fluid whose density scales as R–2, where R is the cosmological scale factor. It is possible that this can result in the “quintessence” effect. ~ Observations The rotation curves, Vrot versus r, of many galaxies are composite, with baryonic material responsible for the inner portion r Rh. Poisson’s equation gives the density structure of a idealized DM halo to be: For r ≤ Rh we adopt r(r) ≈ 〈r〉 and r(r) = /3〈r〉(Rh/r) 2 for Rh ≤ r ≤ R (for Vrot(r) = Vh) . Here R >5 – 10 Rh . Often the luminous underlying galaxy extends to greater than ~1 – 2Rh. As representative, we use values for the Milky Way, Vh = 200 – 210 km/s and Rh ~ 5 kpc, giving 〈r〉 ~ 6 × 10–24 g cm–3 with the luminous matter’s average density clearly exceeding this when r ≤ ~2.5 kpc. TC6875 • A scalar field satisfactorily represents observed halos – An (unquantized) scalar field, f, provides an adequate phenomenological description of the halo DM. Steady-state spatial fluctuations in this field form gravitational potential wells into which baryonic matter may flow, possibly forming luminous galaxies in their center regions. The halos correspond to steady state solutions of the generic field equation: • The field's past history – We suggest that these halos arose as very small amplitude unstable field fluctuations, df ~ 10–4, carried along with the cosmological CDM. With appropriate boundary conditions, the growth of fluctuations is limited by the nonlinear term. Only solutions spherically symmetric in the central regions can grow. From this initial value, it takes ~10 m–1/c ~105 years to develop to finite amplitude, therefore they could not have been important in the very early days of the universe. We assume adequate damping occurs and guess that values of m are determined by values of the local Jeans’ wavenumber associated with the onset of instability of the CDM at the time of radiation-CDM equipartion. c∂tt 2 f−∇2f = m2f(1− f2). (1)