arXiv subjects

Joel E. Tohline

Publications and source records attributed to Joel E. Tohline.

22 records · Page 2Linked to original sources

arXiv2000

Gravitational Waves from Long-Duration Simulations of the Dynamical Bar Instability

Compact astrophysical objects that rotate rapidly may encounter the dynamical ``bar instability.'' The bar-like deformation induced by this rotational instability causes the object to become a potentially strong source of gravitational radiation. We have carried out a set of long-duration simulations of the bar instability with two Eulerian hydrodynamics codes. Our results indicate that the remnant of this instability is a persistent bar-like structure that emits a long-lived gravitational radiation signal.

astro-ph↗

arXiv1998

A Physical Model of Warped Galaxy Disks

Warped H I gas layers in the outer regions of spiral galaxies usually display a noticeably twisted structure. This structure almost certainly arises primarily as a result of differential precession in the H I disk as it settles toward a preferred orientation in an underlying dark halo potential well that is not spherically symmetric. In an attempt to better understand the structure and evolution of these twisted, warped disk structures, we have adopted the "twist-equation" formalism originally developed by Petterson (1977) to study accretion onto compact objects. Utilizing more recent treatments of this formalism, we have generalized the twist-equation to allow for the treatment of non-Keplerian disks and from it have derived a steady-state structure of twisted disks that develops from free precession in a nonspherical, logarithmic halo potential. We have used this steady-state solution to produce H I maps of five galaxies (M83, NGC 300, NGC 2841, NGC 5033, NGC5055), which match the general features of the observed maps of these galaxies quite well. In addition, the model provides an avenue through which the kinematical viscosity of the H I disk and the quadrupole distortion of the dark halo in each galaxy can be quantified. This generalized equation can also be used to examine the time-evolutionary behavior of warped galaxy disks.

astro-ph↗

arXiv1997

The Relative Stability Against Merger of Close, Compact Binaries

The orbital separation of compact binary stars will shrink with time due to the emission of gravitational radiation. This inspiralling phase of a binary system's evolution generally will be very long compared to the system's orbital period, but the final coalescence may be dynamical and driven to a large degree by hydrodynamic effects, particularly if there is a critical separation at which the system becomes dynamically unstable toward merger. Indeed, if weakly relativistic systems (such as white dwarf-white dwarf binaries) encounter a point of dynamical instability at some critically close separation, coalescence may be entirely a classical, hydrodynamic process. Therefore, a proper investigation of this stage of binary evolution must include three-dimensional hydrodynamic simulations. We have constructed equilibrium sequences of synchronously rotating, equal-mass binaries in circular orbit with a single parameter - the binary separation - varying along each sequence. Sequences have been constructed with various polytropic as well as realistic white dwarf and neutron star equations of state. Using a Newtonian, finite-difference hydrodynamics code, we have examined the dynamical stability of individual models along these equilibrium sequences. Our simulations indicate that no points of instability exist on the sequences we analyzed that had relatively soft equations of state (polytropic sequences with polytropic index $n=1.0$ and 1.5 and two white dwarf sequences). However, we did identify dynamically unstable binary models on sequences with stiffer equations of state ($n=0.5$ polytropic sequence and two neutron star sequences). We thus infer that binary systems with soft equations of state are not driven to merger by a dynamical instability.

gr-qc↗

arXiv1995

Millisecond Pulsars: Detectable Sources of Continuous Gravitational Waves?

Laboratory searches for the detection of gravitational waves have focused on the detection of burst signals emitted during a supernova explosion, but have not resulted in any confirmed detections. An alternative approach has been to search for continuous wave (CW) gravitational radiation from the Crab pulsar. In this paper, we examine the possibility of detecting CW gravitational radiation from pulsars and show that nearby millisecond pulsars are generally much better candidates. We show that the minimum strain h_c ~ 10E-26 that can be detected by tuning an antenna to the frequency of the milli- second pulsar PSR 1957+20, with presently available detector technology, is orders of magnitude better than what has been accomplished so far by observing the Crab pulsar, and within an order of magnitude of the maximum strain that may be produced by it. In addition, we point out that there is likely to be a population of rapidly rotating neutron stars (not necessarily radio pulsars) in the solar neighborhood whose spindown evolution is driven by gravitational radiation. We argue that the projected sensitivity of modern resonant detectors is sufficient to detect the subset of this population that lies within 0.1 kpc of the sun.

astro-ph↗