Abstract
In a substantial number of core-collapse supernovae (SNe), early-time interaction indicates a dense circumstellar medium (CSM) that may be produced by outbursts from the progenitor star. ...Wave-driven mass loss is a possible mechanism to produce these signatures, with previous work suggesting that this mechanism is most effective for low-mass (∼11
M
⊙
) SN progenitors. Using one-dimensional hydrodynamic simulations with MESA, we study the effects of this wave heating in SN progenitors of masses
M
ZAMS
= 10–13
M
⊙
. This range encompasses stars that experience semidegenerate central neon burning and more degenerate off-center neon ignition. We find that central Ne ignition at
M
ZAMS
= 11
M
⊙
produces a burst of intense wave heating that transmits ∼10
47
erg of energy at 10 yr before core collapse, whereas other masses experience smaller levels of wave heating. Wave heating does not hydrodynamically drive mass loss in any of our models and is unlikely to produce a very massive CSM on its own. However, wave heating can cause large radial expansion (by more than an order of magnitude), photospheric cooling, and luminosity brightening by up to ∼10
6
L
⊙
in hydrogen-poor stripped star models. Some Type Ib/c progenitors could drastically change their appearance in the final years of their lives, with brightness in the visual bands increasing by nearly 3 mag. Moreover, interaction with a close binary companion could drive intense mass loss, with implications for Type Ibn and other interaction-powered SNe.
Fast radio bursts (FRBs) are an emerging class of short and bright radio transients whose sources remain enigmatic. Within the Galactic Centre, the non-detection of pulsars within the inner ∼10 pc ...has created a missing pulsar problem that has intensified with time. With all reserve, we advance the notion that the two problems could be linked by a common solution: the collapse of neutron stars (NS) due to capture and sedimentation of dark matter (DM) within their cores. Bramante & Linden showed that certain DM properties allow for rapid NS collapse within the high DM density environments near galactic centres while permitting NS survival elsewhere. Each DM-induced collapse could generate an FRB as the NS magnetosphere is suddenly expelled. This scenario could explain several features of FRBs: their short time scales, large energies, locally produced scattering tails, and high event rates. We predict that FRBs are localized to galactic centres, and that our own galactic centre harbours a large population of NS-mass (M ∼ 1.4 M⊙) black holes. The DM-induced collapse scenario is intrinsically unlikely because it can only occur in a small region of allowable DM parameter space. However, if observed to occur, it would place tight constraints on DM properties.
ABSTRACT
In some semidetached binary systems, the donor star may transfer mass to the companion at a very high rate. We propose that, at sufficiently high mass-transfer rates such that the accretion ...disc around the companion becomes geometrically thick (or advection-dominated) near the disc outer radius, a large fraction of the transferred mass may be lost through the outer Lagrangian (L2) point, as a result of the excessive energy generated by viscous heating that cannot be efficiently radiated away. A physical model is constructed where the L2 mass-loss fraction is given by the requirement that the remaining material in the disc has Bernoulli number equal to the L2 potential energy. Our model predicts significant L2 mass-loss at mass transfer rates exceeding $\mbox{a few}\, 10^{-4}\, {\mathrm{ M}_\odot \, \mathrm{yr}^{-1}}$. An equatorial circumbinary outflow (CBO) is formed in these systems. Implications for the orbital evolution and the observational appearance of the system are discussed. In particular, (1) rapid angular momentum loss from the system tends to shrink the orbit, and hence may increase the formation rate of mergers and gravitational-wave sources; and (2) photons from the hot disc wind are reprocessed by the CBO into longer wavelength emission in the infrared bands, consistent with Spitzer observations of some ultra-luminous X-ray sources.
ABSTRACT The core rotation rates of massive stars have a substantial impact on the nature of core-collapse (CC) supernovae and their compact remnants. We demonstrate that internal gravity waves ...(IGWs), excited via envelope convection during a red supergiant phase or during vigorous late time burning phases, can have a significant impact on the rotation rate of the pre-SN core. In typical ( ) supernova progenitors, IGWs may substantially spin down the core, leading to iron core rotation periods . Angular momentum (AM) conservation during the supernova would entail minimum NS rotation periods of . In most cases, the combined effects of magnetic torques and IGW AM transport likely lead to substantially longer rotation periods. However, the stochastic influx of AM delivered by IGWs during shell burning phases inevitably spin up a slowly rotating stellar core, leading to a maximum possible core rotation period. We estimate maximum iron core rotation periods of in typical CC supernova progenitors, and a corresponding spin period of for newborn neutron stars (NSs). This is comparable to the typical birth spin periods of most radio pulsars. Stochastic spin-up via IGWs during shell O/Si burning may thus determine the initial rotation rate of most NSs. For a given progenitor, this theory predicts a Maxwellian distribution in pre-collapse core rotation frequency that is uncorrelated with the spin of the overlying envelope.
Gravity waves in strong magnetic fields Rui, Nicholas Z; Fuller, Jim
Monthly notices of the Royal Astronomical Society,
05/2023, Letnik:
523, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
Strong magnetic fields in the cores of stars are expected to significantly modify the behaviour of gravity waves: this is likely the origin of suppressed dipole modes observed in many red ...giants. However, a detailed understanding of how such fields alter the spectrum and spatial structure of magnetogravity waves has been elusive. For a dipole field, we analytically characterize the horizontal eigenfunctions of magnetogravity modes, assuming that the wavevector is primarily radial. For axisymmetric modes (m = 0), the magnetogravity wave eigenfunctions become Hough functions, and they have a radial turning point for sufficiently strong magnetic fields. For non-axisymmetric modes (m ≠ 0), the interaction between the discrete g-mode spectrum and a continuum of Alfvén waves produces nearly discontinuous features in the fluid displacements at critical latitudes associated with a singularity in the fluid equations. We find that magnetogravity modes cannot propagate in regions with sufficiently strong magnetic fields, instead becoming evanescent. When encountering strong magnetic fields, ingoing gravity waves are likely refracted into outgoing slow magnetic waves. These outgoing waves approach infinite radial wavenumbers, which are likely to be damped efficiently. However, it may be possible for a small fraction of the wave power to escape the stellar core as pure Alfvén waves or magnetogravity waves confined to a very narrow equatorial band. The artificially sharp features in the Wentzel–Kramers–Brillouin-separated solutions suggest the need for global mode solutions which include small terms neglected in our analysis.
ABSTRACT
Stellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be ...distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have overmassive envelopes relative to their cores, which is manifested asteroseismically by a g-mode period spacing smaller than expected for the star’s mass. Remnants of mergers that occur when the primary is still on the main sequence or whose total mass is less than $\approx \! 2 \, {\rm M}_\odot$ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogues of Vrard, Mosser & Samadi and Yu et al., we identify 24 promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.
ABSTRACT KIC 3230227 is a short period (P 7.0 days) eclipsing binary with a very eccentric orbit (e = 0.6). From combined analysis of radial velocities and Kepler light curves, this system is found ...to be composed of two A-type stars, with masses of M1 = 1.84 0.18 M , M2 = 1.73 0.17 M and radii of R1 = 2.01 0.09 R , R2 = 1.68 0.08 R for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat star system. After removing the binary light curve model, more than 10 pulsational frequencies are present in the Fourier spectrum of the residuals, and most of them are integer multiples of the orbital frequency. These pulsations are tidally driven, and both the amplitudes and phases are in agreement with predictions from linear tidal theory for l = 2, m = −2 prograde modes.
Tidal interactions between moons and planets can have major effects on the orbits, spins, and thermal evolution of the moons. In the Saturn system, tidal dissipation in the planet transfers angular ...momentum from Saturn to the moons, causing them to migrate outwards. The rate of migration is determined by the mechanism of dissipation within the planet, which is closely tied to the planet’s uncertain structure. We review current knowledge of giant planet internal structure and evolution, which has improved thanks to data from the
Juno
and
Cassini
missions. We discuss general principles of tidal dissipation, describing both equilibrium and dynamical tides, and how dissipation can occur in a solid core or a fluid envelope. Finally, we discuss the possibility of resonance locking, whereby a moon can lock into resonance with a planetary oscillation mode, producing enhanced tidal migration relative to classical theories, and possibly explaining recent measurements of moon migration rates.
Abstract
Tidal dissipation in binary star and planetary systems is poorly understood. Fortunately, eccentric binaries known as heartbeat stars often exhibit tidally excited oscillations, providing ...observable diagnostics of tidal circularization mechanisms and time-scales. We apply tidal theories to observations of the heartbeat star KIC 8164262, which contains an F-type primary in a very eccentric orbit that exhibits a prominent tidally excited oscillation. We demonstrate that the prominent oscillation is unlikely to result from a chance resonance between tidal forcing and a stellar oscillation mode. However, the oscillation has a frequency and amplitude consistent with the prediction of resonance locking, a mechanism in which coupled stellar and orbital evolution maintain a stable resonance between tidal forcing and a stellar oscillation mode. The resonantly excited mode produces efficient tidal dissipation (corresponding to an effective tidal quality factor Q ∼ 5 × 104), such that tidal orbital decay/circularization proceeds on a stellar evolution time-scale.
Abstract
Many core-collapse supernovae (SNe) with hydrogen-poor and low-mass ejecta, such as ultra-stripped SNe and type Ibn SNe, are observed to interact with dense circumstellar material (CSM). ...These events likely arise from the core collapse of helium stars that have been heavily stripped by a binary companion and have ejected significant mass during the last weeks to years of their lives. In helium star models run to days before core collapse we identify a range of helium core masses ≈2.5–3
M
⊙
whose envelopes expand substantially due to the helium shell burning while the core undergoes neon and oxygen burning. When modeled in binary systems, the rapid expansion of these helium stars induces extremely high rates of late-stage mass transfer (
M
̇
≳
10
−
2
M
⊙
yr
−
1
) beginning weeks to decades before core collapse. We consider two scenarios for producing CSM in these systems: either mass transfer remains stable and mass loss is driven from the system in the vicinity of the accreting companion, or mass transfer becomes unstable and causes a common envelope event (CEE) through which the helium envelope is unbound. The ensuing CSM properties are consistent with the CSM masses (∼10
−2
–1
M
⊙
) and radii (∼10
13
–10
16
cm) inferred for ultra-stripped SNe and several type Ibn SNe. Furthermore, systems that undergo a CEE could produce short-period neutron star binaries that merge in less than 100 Myr.
PDF
