The Formation of Black-Hole X-Ray Transients

Studies of the observed characteristics of black-hole (BH) X-ray binaries can be provide us with valuable information about the process of BH formation. In this paper I address some of the aspects of our current understanding of BH formation in binaries and point out some of the existing problems of current theoretical models. In particular, the measured orbital periods and donor-star properties indicate that a common-envelope phase appears to be a necessary ingredient of the evolutionary history of observed BH X-ray transients, and that it must be associated only with a modest orbital contraction. The timing of this common-envelope phase is crucial in determining the final BH masses and current evolutionary models of mass-losing massive stars place strong constraints on the possible masses for immediate BH progenitors and wind mass loss from helium stars. Last, it is interesting that, even in the absence of any source of mass loss, the highest helium-star masses predicted by current evolutionary models are still not high enough to account for the measured BH mass in V404 Cyg (>10 solar masses). An alternative for the formation of relatively massive BH may be provided by the evolutionary sequence proposed by Eggleton & Verbunt (1986), which invokes hierarchical triples as progenitors of BH X-ray binaries with low-mass companions.Comment: 10 pages, 3 figures, to appear in Evolution of Binary and Multiple Star Systems, ASP Conf.Series, 2001, P. Podsiadlowski et al. (eds.) (proceedings from a Meeting in Celebration of Peter Eggleton's 60th Birthday

Compact Binary Mergers and Accretion-Induced Collapse: Event Rates

This paper is a brief review of the topic of binary systems as sources of gravitational-wave emission for both LIGO and LISA. In particular I review the current estimates of the associated Galactic event rates and their implications for expected detection rates. I discuss the estimates for (i) the coalescence of close binaries containing neutron stars or black holes, (ii) white dwarfs going through accretion-induced collapse into neutron stars, and (iii) detached but close binaries containing two white dwarfs. The relevant uncertainties and robustness of the estimates are addressed along with ways of obtaining conservative upper limits.Comment: 10 pages, 2 figures included, to appear in the proceedings of the 3rd Amaldi Conference on Gravitational Wave

Event Rates for Binary Inspiral

Double compact objects (neutron stars and black holes) found in binaries with small orbital separations are known to spiral in and are expected to coalesce eventually because of the emission of gravitational waves. Such inspiral and merger events are thought to be primary sources for ground based gravitational-wave interferometric detectors (such as LIGO). Here, we present a brief review of estimates of coalescence rates and we examine the origin and relative importance of uncertainties associated with the rate estimates. For the case of double neutron star systems, we compare the most recent rate estimates to upper limits derived in a number of different ways. We also discuss the implications of the formation of close binaries with two non-recycled pulsars.Comment: 12 pages, to appear in AIP proceedings ``Astrophysical Sources of Gravitational Radiation for Ground-Based Detectors.'

Adiabatic Mass Loss and the Outcome of the Common Envelope Phase of Binary Evolution

We have developed a new method for calculating common envelope (CE) events based on explicit consideration of the donor star's structural response to adiabatic mass loss. In contrast to existing CE prescriptions, which specify a priori the donor's remnant mass, we determine this quantity self-consistently and find it depends on binary and CE parameters. This aspect of our model is particularly important to realistic modeling for upper main sequence star donors without strongly degenerate cores (and hence without a clear core/envelope boundary). We illustrate the central features of our method by considering CE events involving 10 solar mass donors on or before their red giant branch. For such donors, the remnant core mass can be as much as 30% larger than the star's He-core mass. Applied across a population of such binaries, our methodology results in a significantly broader remnant mass and final orbital separation distribution and a 20% increase in CE survival rates as compared to previous prescriptions for the CE phase.Comment: 4 pages, 3 figures; corrected typo in equation (1); updated reference dat