Orbital Decay Timescale Research Articles

Orbital Decay of the PSR J0045−7319 Binary System: Age of Radio Pulsar and Initial Spin of Neutron Star

Recent timing observations of PSR J0045-7319 reveal that the neutron star/B star binary orbit is decaying on a timescale of |Porb/orb| = 0.5 Myr, shorter than the characteristic age (τc = 3 Myr) of the pulsar. We study mechanisms for the orbital decay. The standard weak-friction theory based on static tide requires far too short a viscous time to explain the observed orb. We show that dynamical tidal excitation of g-modes in the B star can be responsible for the orbital decay. However, to explain the observed short decay timescale, the B star must have some significant retrograde rotation with respect to the orbit—the retrograde rotation brings lower order g-modes, which couple much more strongly to the tidal potential, into closer resonances with the orbital motion, thus significantly enhancing the dynamical tide. A much less likely possibility is that the g-mode damping time is much shorter than the ordinary radiative damping time. The observed orbital decay timescale combined with a generic orbital evolution model based on dynamical tide can be used as a timer, yielding an upper limit of 1.4 Myr on the age of the binary system since the neutron star's formation. Thus the characteristic age of the pulsar is not a good age indicator. Assuming standard magnetic dipole braking for the pulsar and no significant magnetic field decay on a timescale 1 Myr, the upper limit for the age implies that the initial spin of the neutron star at birth was close to its current value.

Common-Envelope Evolution, the Formation of CVs, LMXBs, and the Fate of HMXBs

Recent three-dimensional studies of the common-envelope phase of binary evolution have provided important insights into its theoretical description. The role of non-axisymmetric effects associated with gravitational torques is essential for understanding all aspects of the evolution. For successful ejection of the common envelope and survival of the remnant compact binary it is required that the orbital period of the progenitor system is long, so that one of the components of the system is in the red giant or red supergiant stage of evolution. Not only must there be sufficient energy released from the orbit to unbind the common envelope, but it is also necessary that a sufficiently steep density gradient exist above the evolved core of the giant. If these conditions are satisfied, the time scale for orbital decay in the region above the core exceeds the time scale for mass loss from the common envelope and merger is avoided. The implications of these results for the formation of cataclysmic variables (CVs), low-mass X-ray binaries (LMXBs), and the descendants of high-mass X-ray binaries (HMXBs) are discussed.

Double core evolution. 7: The infall of a neutron star through the envelope of its massive star companion

view Abstract Citations (61) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Double Core Evolution. VII. The Infall of a Neutron Star through the Envelope of Its Massive Star Companion Terman, James L. ; Taam, Ronald E. ; Hernquist, Lars Abstract Binary systems with properties similar to those of high-mass X-ray binaries are evolved through the common envelope phase. Three-dimensional simulations show that the timescale of the infall phase of the neutron star depends upon the evolutionary state of its massive companion. We find that tidal torques more effectively accelerate common envelope evolution for companions in their late core helium-burning stage and that the infall phase is rapid (approximately several initial orbital periods). For less evolved companions the decay of the orbit is longer; however, once the neutron star is deeply embedded within the companion's envelope the timescale for orbital decay decreases rapidly. As the neutron star encounters the high-density region surrounding the helium core of its massive companion, the rate of energy loss from the orbit increases dramatically leading to either partial or nearly total envelope ejection. The outcome of the common envelope phase depends upon the structure of the evolved companion. In particular, it is found that the entire common envelope can be ejected by the interaction of the neutron star with a red supergiant companion in binaries with orbital periods similar to those of long-period Be X-ray binaries. For orbital periods greater than or approximately equal to 0.8-2 yr (for companions of mass 12-24 solar mass) it is likely that a binary will survive the common envelope phase. For these systems, the structure of the progenitor star is characterized by a steep density gradient above the helium core, and the common envelope phase ends with a spin up of the envelope to within 50%-60% of corotation and with a slow mass outflow. The efficiency of mass ejection is found to be approximately 30%-40%. For less evolved companions, there is insufficient energy in the orbit to unbind the common envelope and only a fraction of it is ejected. Since the timescale for orbital decay is always shorter than the mass-loss timescale from the common envelope, the two cores will likely merge to form a Thorne-Zytkow object. Implications for the origin of Cyg X-3, an X-ray source consisting of a Wolf-Rayet star and a compact companion, and for the fate of the remnant binary consisting of a helium star and a neutron star are briefly discussed. Publication: The Astrophysical Journal Pub Date: May 1995 DOI: 10.1086/175702 Bibcode: 1995ApJ...445..367T Keywords: Binary Stars; Neutron Stars; Orbit Decay; Stellar Envelopes; Stellar Evolution; Stellar Interiors; Stellar Mass Ejection; Density Distribution; Energy Distribution; Hydrodynamics; Orbital Mechanics; Radiation Pressure; Astrophysics; HYDRODYNAMICS; STARS: BINARIES: CLOSE; STARS: EVOLUTION; STARS: INTERIORS; STARS: NEUTRON full text sources ADS | data products SIMBAD (4) Related Materials (9) Part 1: 1978ApJ...222..269T Part 2: 1984ApJ...280..771B Part 3: 1989ApJ...337..849T Part 4: 1991ApJ...373..246T Part 5: 1994ApJ...422..729T Part 6: 1994ApJ...431..247T Part 8: 1995ApJ...451..308Y Part 9: 1996ApJ...458..692T Part 10: 1998ApJ...500..909S

The fate of central black holes in merging galaxies

This paper presents results of a series of numerical N-body experiments that describe the merging of galaxy pairs containing a massive black hole in their core. The aim is to study the orbital evolution of the two black holes through the merger event. It is found that merging does NOT lead to the formation of a CLOSE black hole pair} at the center of the remnant when the two progenitor galaxies have (1) similar masses, (2) different central densities, and (3) relative orbit with non zero angular momentum. Under these conditions, the central black hole of the less dense galaxy settles into an wide orbit, i.e., at a distance from the center comparable to the half mass radius of the remnant, where the time scale for orbital decay by dynamical friction can be several Gyrs. The implications of this result are briefly discussed.

A dynamical instability model for the period gap of cataclysmic variable binary sytems

view Abstract Citations (10) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Dynamical Instability Model for the Period Gap of Cataclysmic Variable Binary Systems Taam, Ronald E. ; McDermott, P. N. Abstract A dynamical instability in a convective secondary is proposed as an explanation of the period gap of cataclysmic variable systems. It is demonstrated that if, during the course of evolution of the binary system, the secondary component detaches from its Roche lobe when it is fully convective, then at the next onset of mass transfer a dynamical instability may ensue. It is shown that such a system at orbital period near 3 hr will be unstable to mass transfer and that stability will be regained at longer orbital periods when the system becomes detached. If the time scale for orbital decay by angular momentum losses associated with gravitational radiation and/or a magnetically coupled stellar wind is shorter than the Hubble time, the system will then resume mass transfer at periods near 2 hr. Publication: The Astrophysical Journal Pub Date: August 1987 DOI: 10.1086/184959 Bibcode: 1987ApJ...319L..83T Keywords: Binary Stars; Cataclysmic Variables; Dynamic Stability; Gravitational Waves; Mass Transfer; Angular Momentum; Roche Limit; Stellar Luminosity; Stellar Mass; Stellar Winds; White Dwarf Stars; Astrophysics; INSTABILITIES; STARS: BINARIES; STARS: VARIABLES full text sources ADS |