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Register a new userSpin-orbit misalignment from triple-star common envelope evolution
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Authors
Noam Soker
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I study a triple star common envelope evolution (CEE) of a tight binary system that is spiraling-in inside a giant envelope and launches jets that spin-up the envelope with an angular momentum component perpendicular to the orbital angular momentum of the triple star system. This occurs when the orbital plane of the tight binary system and that of the triple star system are inclined to each other, so the jets are not along the triple star orbital angular momentum. The merger of the tight binary stars also tilts the envelope spin direction. If the giant is a red supergiant (RSG) star that later collapses to form a black hole (BH) the BH final spin is misaligned with the orbital angular momentum. Therefore, CEE of neutron star (NS) or BH tight binaries with each other or with one main sequence star (MSS) inside the envelope of an RSG, where the jets power a common envelope jets supernova (CEJSN) event, might end with a NS/BH - NS/BH close binary system with spin-orbit misalignment. Such binaries can later merge to be gravitational waves sources. I list five triple star scenarios that might lead to spin-orbit misalignments of NS/BH - NS/BH binary systems, two of which predict that the two spins be parallel to each other. In the case of a tight binary system of two MSSs inside an asymptotic giant branch star the outcome is an additional non-spherical component to the mass loss with the formation of a messy planetary nebula.
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Common envelope (CE) is an important phase in the evolution of interacting evolved binary systems. The interaction of the binary components during the CE evolution (CEE) stage gives rise to orbital inspiral and the formation of a short-period binary or a merger, on the expense of extending and/or ejecting the envelope. CEE is not well understood, as hydrodynamical simulations show that only a fraction of the CE-mass is ejected during the dynamical inspiral, in contrast with observations of post-CE binaries. Different CE models suggest different timescales are involved in the CE-ejection, and hence a measurement of the CE-ejection timescale could provide direct constraints on the CEE-process. Here we propose a novel method for constraining the mass-loss timescale of the CE, using post-CE binaries which are part of wide-orbit triple systems. The orbit/existence of a third companion constrains the CE mass-loss timescale, since rapid CE mass-loss may disrupt the triple system, while slower CE mass-loss may change the orbit of the third companion without disrupting it. As first test-cases we examine two observed post-CE binaries in wide triples, Wolf-1130 and GD-319. We follow their evolution due to mass-loss using analytic and numerical tools, and consider different mass-loss functions. We calculate a wide grid of binary parameters and mass-loss timescales in order to determine the most probable mass-loss timescale leading to the observed properties of the systems. We find that mass-loss timescales of the order of $10^{3}-10^{5}{rm yr}$ are the most likely to explain these systems. Such long timescales are in tension with most of the CE mass-loss models, which predict shorter, dynamical timescales, but are potentially consistent with the longer timescales expected from the dust-driven winds model for CE ejection.
Over forty years of research suggests that the common envelope phase, in which an evolved star engulfs its companion upon expansion, is the critical evolutionary stage forming short-period, compact-object binary systems, such as coalescing double compact objects, X-ray binaries, and cataclysmic variables. In this work, we adapt the one-dimensional hydrodynamic stellar evolution code, MESA, to model the inspiral of a 1.4M$_{odot}$ neutron star (NS) inside the envelope of a 12$M_{odot}$ red supergiant star. We self-consistently calculate the drag force experienced by the NS as well as the back-reaction onto the expanding envelope as the NS spirals in. Nearly all of the hydrogen envelope escapes, expanding to large radii ($sim$10$^2$ AU) where it forms an optically thick envelope with temperatures low enough that dust formation occurs. We simulate the NS orbit until only 0.8M$_{odot}$ of the hydrogen envelope remains around the giant stars core. Our results suggest that the inspiral will continue until another $approx$0.3M$_{odot}$ are removed, at which point the remaining envelope will retract. Upon separation, a phase of dynamically stable mass transfer onto the NS accretor is likely to ensue, which may be observable as an ultraluminous X-ray source. The resulting binary, comprised of a detached 2.6M$_{odot}$ helium-star and a NS with a separation of 3.3-5.7R$_{odot}$, is expected to evolve into a merging double neutron-star, analogous to those recently detected by LIGO/Virgo. For our chosen combination of binary parameters, our estimated final separation (including the phase of stable mass transfer) suggests a very high $alpha_{rm CE}$-equivalent efficiency of $approx$5.
Stars hosting hot Jupiters are often observed to have high obliquities, whereas stars with multiple co-planar planets have been seen to have low obliquities. This has been interpreted as evidence that hot-Jupiter formation is linked to dynamical disruption, as opposed to planet migration through a protoplanetary disk. We used asteroseismology to measure a large obliquity for Kepler-56, a red giant star hosting two transiting co-planar planets. These observations show that spin-orbit misalignments are not confined to hot-Jupiter systems. Misalignments in a broader class of systems had been predicted as a consequence of torques from wide-orbiting companions, and indeed radial-velocity measurements revealed a third companion in a wide orbit in the Kepler-56 system.
The observational appearance of black holes in X-ray binary systems depends on their masses, spins, accretion rate and the misalignment angle between the black hole spin and the orbital angular momentum. We used high-precision optical polarimetric observations to constrain the position angle of the orbital axis of the black hole X-ray binary MAXI J1820+070. Together with previously obtained orientation of the relativistic jet and the inclination of the orbit this allowed us to determine a lower limit of 40 degrees on the misalignment angle. Such a large misalignment challenges the models of quasi-periodic oscillations observed in black hole X-ray binaries, puts strong constraints on the black hole formation mechanisms, and has to be accounted for when measuring black hole masses and spins from the X-ray data.
We present a new model describing the evolution of triple stars which undergo common envelope evolution, using a combination of analytic and numerical techniques. The early stages of evolution are driven by dynamical friction with the envelope, which causes the outer triple orbit to shrink faster than the inner binary. In most cases, this leads to a chaotic dynamical interaction between the three stars, culminating in the ejection of one of the stars from the triple. This ejection and resulting recoil on the remnant binary are sufficient to eject all three stars from the envelope, which expands and dissipates after the stars have escaped. These results have implications for the properties of post-common envelope triples: they may only exist in cases where the envelope was ejected before the onset of dynamical instability, the likelihood of which depends on the initial binary separation and the envelope structure. In cases where the triple becomes dynamically unstable, the triple does not survive and the envelope dissipates without forming a planetary nebula.
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