7,094 research outputs found
Peculiar Velocity and Deaberration of the Sky
Recent studies have found the earth's peculiar velocity to be significant in
microwave background based tests for compact cosmic topology, and modifications
to these tests have been proposed. Tests of non-gaussianity, weak lensing
analysis and new tests using improved CMB data will also be sensitive to
peculiar velocity. We propose here to simplify matters by showing how to
construct a deaberrated CMB map to which any test requiring a Hubble flow
viewpoint can be applied without further complication. In a similar manner
deaberration can also be applied to object surveys used for example in
topological searches and matter distribution analysis. In particular we have
produced a revised list of objects with z > 1.0 using the NASA/IPAC
Extragalactic Database.Comment: 8 pages, 1 figure, v4 accepted by Ap
Nuclear Equation of State and Internal Structure of Magnetars
Recently, neutron stars with very strong surface magnetic fields have been
suggested as the site for the origin of observed soft gamma repeaters (SGRs).
We investigate the influence of a strong magnetic field on the properties and
internal structure of such strongly magnetized neutron stars (magnetars). The
presence of a sufficiently strong magnetic field changes the ratio of protons
to neutrons as well as the neutron appearance density. We also study the pion
production and pion condensation in a strong magnetic field. We discuss the
pion condensation in the interior of magnetars as a possible source of SGRs.Comment: 5 pages with 3 figures, To appear in the Proceedings of the 5th
Huntsville Gamma Ray Burst Symposium, Huntsville, Alabama, USA, Oct. 18-22,
199
Absence of a Lower Limit on Omega_b in Inhomogeneous Primordial Nucleosynthesis
We show that a class of inhomogeneous big bang nucleosynthesis models exist
which yield light-element abundances in agreement with observational
constraints for baryon-to-photon ratios significantly smaller than those
inferred from standard homogeneous big bang nucleosynthesis (HBBN). These
inhomogeneous nucleosynthesis models are characterized by a bimodal
distribution of baryons in which some regions have a local baryon-to-photon
ratio eta=3*10e-10, while the remaining regions are baryon-depleted. HBBN
scenarios with primordial (2H+3He)/H<9*10e-5 necessarily require that most
baryons be in a dark or non-luminous form, although new observations of a
possible high deuterium abundance in Lyman-alpha clouds may relax this
requirement somewhat. The models described here present another way to relax
this requirement and can even eliminate any lower bound on the baryon-to-photon
ratio.Comment: 13 pages, 2 figures (available upon request by email), plain te
Stellar Orbits and the Interstellar Gas Temperature in Elliptical Galaxies
We draw attention to the close relationship between the anisotropy parameter
beta(r) for stellar orbits in elliptical galaxies and the temperature profile
T(r) of the hot interstellar gas. For nearly spherical galaxies the gas density
can be accurately determined from X-ray observations and the stellar luminosity
density can be accurately found from the optical surface brightness. The Jeans
equation and hydrostatic equilibrium establish a connection between beta(r) and
T(r) that must be consistent with the observed stellar velocity dispersion.
Purely optical observations of the bright elliptical galaxy NGC 4472 indicate
beta(r) < 0.35 within the effective radius. However, the X-ray gas temperature
profile T(r) for NGC 4472 requires significantly larger anisotropy, beta = 0.6
- 0.7, about twice the optical value. This strong preference for radial stellar
orbits must be understood in terms of the formation history of massive
elliptical galaxies. Conversely, if the smaller, optically determined
anisotropy is indeed correct, we are led to the important conclusion that the
temperature profile T(r) of the hot interstellar gas in NGC 4472 must differ
from that indicated by X-ray observations, or that the hot gas is not in
hydrostatic equilibrium.Comment: 6 pages (emulateapj5) with 4 figures; accepted by The Astrophysical
Journa
Enhanced Heavy-Element Formation in Baryon-Inhomogeneous Big-Bang Models
We show that primordial nucleosynthesis in baryon inhomogeneous big-bang
models can lead to significant heavy-element production while still satisfying
all the light-element abundance constraints including the low lithium abundance
observed in population II stars. The parameters which admit this solution arise
naturally from the process of neutrino induced inflation of baryon
inhomogeneities prior to the epoch of nucleosynthesis. These solutions entail a
small fraction of baryons (\le 2\%) in very high density regions with local
baryon-to-photon ratio , while most baryons are at a
baryon-to-photon ratio which optimizes the agreement with light-element
abundances. The model would imply a unique signature of baryon inhomogeneities
in the early universe, evidenced by the existence of primordial material
containing heavy-element products of proton and alpha- burning reactions with
an abundance of .Comment: 19 pages in plain Tex, 5 figures (not included) available by fax or
mail upon request, ApJ in press, L
- âŠ