Large Angular Scale Polarization of the Cosmic Microwave Background and the Feasibility of its Detection

In addition to its spectrum and temperature anisotropy, the 2.7K Cosmic Microwave Background is also expected to exhibit a low level of polarization. The spatial power spectrum of the polarization can provide details about the formation of structure in the universe as well as its ionization history. Here we calculate the magnitude of the CMB polarization in various cosmological scenarios, with both an analytic and a numerical method. We then outline the fundemental challenges to measuring these signals and focus on two of them: achieving adequate sensitivity and removing contamination from foreground sources. We then describe the design of a ground based instrument (POLAR) that could detect polarization of the CMB at large angular scales in the new few years.Comment: 40 pages, 7 figures, accepted for publication in the Astrophysical Journa

Response of a spaceborne gravitational wave antenna to solar oscillations

We investigate the possibility of observing very small amplitude low frequency solar oscillations with the proposed laser interferometer space antenna (LISA). For frequencies $\nu$ below $3\times 10^{-4} {\rm Hz}$ the dominant contribution is from the near zone time dependent gravitational quadrupole moments associated with the normal modes of oscillation. For frequencies $\nu$ above $3\times 10^{-4} {\rm Hz}$ the dominant contribution is from gravitational radiation generated by the quadrupole oscillations which is larger than the Newtonian signal by a factor of the order $(2 \pi r \nu/ c)^4$, where $r$ is the distance to the Sun, and $c$ is the velocity of light. The low order solar quadrupole pressure and gravity oscillation modes have not yet been detected above the solar background by helioseismic velocity and intensity measurements. We show that for frequencies $\nu \lesssim 2\times 10^{-4} {\rm Hz}$, the signal due to solar oscillations will have a higher signal to noise ratio in a LISA type space interferometer than in helioseismology measurements. Our estimates of the amplitudes needed to give a detectable signal on a LISA type space laser interferometer imply surface velocity amplitudes on the sun of the order of 1-10 mm/sec in the frequency range $1\times 10^{-4} -5\times 10^{-4} {\rm Hz}$. If such modes exist with frequencies and amplitudes in this range they could be detected with a LISA type laser interferometer.Comment: 16 pages, 6 figures, 1 table. A reworked and considerably improved version of ArXiv:astro-ph/0103472, Published in PR

Hydrodynamics of primordial black hole formation

The hydrodynamic picture of the formation of primordial black holes (PBH) at the early stages of expansion of the Universe is considered. It is assumed that close to singularity, expansion occurs in a quasi-isotropic way. Using an EVM, a spherically symmetrical nonlinear problem of the evolution of primary strong deviation from the Fridman solution was solved. What these deviations must be, so that the formation of PBH occurred was clarified. Attention was devoted to the role of pressure gradients. It is pointed out that at the moment of formation of PBH, only a small part of matter enters into it, primarily the component of perturbation. It is also pointed out that at this moment, the mass of PBH essentially is smaller than the mass considered within the cosmic horizon. The possibility of changing the mass of the PBH as a result of accretion is analyzed

The evolution of a binary in a retrograde circular orbit embedded in an accretion disk

Supermassive black hole binaries may form as a consequence of galaxy mergers. Both prograde and retrograde orbits have been proposed. We study a binary of a small mass ratio, q, in a retrograde orbit immersed in and interacting with a gaseous accretion disk in order to estimate time scales for inward migration leading to coalescence and the accretion rate to the secondary component. We employ both semi-analytic methods and two dimensional numerical simulations, focusing on the case where the binary mass ratio is small but large enough to significantly perturb the disk. We develop the theory of type I migration for this case and determine conditions for gap formation finding that then inward migration occurs on a time scale equal to the time required for one half of the secondary mass to be accreted through the unperturbed disk, with accretion onto the secondary playing only a minor role. The semi-analytic and fully numerical approaches are in good agreement, the former being applicable over long time scales. Inward migration induced by interaction with the disk alleviates the final parsec problem. Accretion onto the secondary does not significantly affect the orbital evolution, but may have observational consequences for high accretion efficiency. The binary may then appear as two sources of radiation rotating around each other. This study should be extended to consider orbits with significant eccentricity and the effects of gravitational radiation at small length scales. Note too that torques acting between a circumbinary disk and a retrograde binary orbit may cause the mutual inclination to increase on a timescale that can be similar to, or smaller than that for orbital evolution, depending on detailed parameters. This is also an aspect for future study (abridged).Comment: 24 pages, 18 figures, accepted for publication in A&A. For movies of the simulations see http://astro.qmul.ac.uk/people/sijme-jan-paardekooper/publication

On the origin of kinematic distribution of the sub-parsec young stars in the Galactic center

Within a half-parsec from the Galactic center (GC), there is a population of coeval young stars which appear to reside in a coherent disk. Surrounding this dynamically-cool stellar system, there is a population of stars with a similar age and much larger eccentricities and inclinations relative to the disk. We propose a hypothesis for the origin of this dynamical dichotomy. Without specifying any specific mechanism, we consider the possibility that both stellar populations were formed within a disk some 6 Myr ago. But this orderly structure was dynamically perturbed outside-in by an intruding object with a mass ~10^4 Msun, which may be an intermediate-mass black hole (IMBH) or a dark stellar cluster hosting an IMBH. We suggest that the perturber migrated inward to ~0.15-0.3pc from the GC under the action of dynamical friction. Along the way, it captured many stars in the outer disk region into its mean-motion resonance, forced them to migrate with it, closely encountered with them, and induced the growth of their eccentricity and inclination. But stars in the inner regions of the disk retain their initial coplanar structure. We predict that some of the inclined and eccentric stars surrounding the disk may have similar Galactocentric semimajor axis. Future precision determination of their kinematic distribution of these stars will not only provide a test for this hypothesis but also evidences for the presence of an IMBH or a dark cluster at the immediate proximity of the massive black hole at the GC. (abridged)Comment: 14 pages, including 13 figures, typo corrected, reference added, ApJ in pres