Centrifugal Breakup Research Articles

A Broadband X-Ray Investigation of Fast-spinning Intermediate Polar CTCV J2056–3014

We report on XMM-Newton, NuSTAR, and NICER X-ray observations of CTCV J2056–3014, a cataclysmic variable (CV) with one of the fastest-spinning white dwarfs (WDs) at P = 29.6 s. While previously classified as an intermediate polar, CJ2056 also exhibits the properties of WZ Sge–type CVs, such as dwarf novae and superoutbursts. With XMM-Newton and NICER, we detected the spin period up to ∼2 keV with 7σ significance. We constrained its derivative to |Ṗ|<1.8×10−12 s s−1 after correcting for binary orbital motion. The pulse profile is characterized by a single broad peak with ∼25% modulation. NuSTAR detected a fourfold increase in unabsorbed X-ray flux coincident with an optical flare, in 2022 November. The XMM-Newton and NICER X-ray spectra at 0.310 keV are best characterized by an absorbed, optically thin three-temperature thermal plasma model (kT = 0.3, 1.0, and 4.9 keV), while the NuSTAR spectra at 3–30 keV are best fit by a single-temperature thermal plasma model (kT = 8.4 keV), both with Fe abundance Z Fe/Z ⊙ = 0.3. CJ2056 exhibits similarities to other fast-spinning CVs, such as low plasma temperatures and no significant X-ray absorption at low energies. As the WD’s magnetic field strength is unknown, we applied both nonmagnetic and magnetic CV spectral models (MKCFLOW and MCVSPEC) to determine the WD mass. The derived WD mass range (M = 0.7–1.0 M ⊙) is above the centrifugal breakup mass limit of 0.56 M ⊙ and consistent with the mean WD mass of local CVs (M ≈ 0.8–0.9 M ⊙).

Is (3599) Basov a large C-type super-fast rotator?

The rubble-pile model of asteroids deduced from the existence of a spin cutoff is an important paradigm in the interior structure of asteroids as a consequence of their collisional evolution. Many objects with size less than 200 ​m have been found to be rotating with a spin period less than 2.2 ​h but seldom so for bigger objects. Thus, asteroids with rotation periods significantly less than this spin cutoff limit are called super-fast rotators. Most often this picture of spin cutoff and hence the rubble-pile model has been applied to the S-type asteroids. In this study, we report the interesting case of (3599) Basov which is a member of the Themis family of C-class composition. The spin barrier of the Themis family asteroids has been shown to be P ​= ​3 ​h. What is unusual about (3599) Basov is that its rotation period has been confirmed to be P ​= ​2.157 ​± ​0.037 ​h which is significantly shorter than the critical value for centrifugal breakup. Furthermore, its size of 18 ​km is much larger than those of the S-class super-fast rotators. The physical property of (3599) Basov might therefore be quite unique. • C-type asteroids of rubble-pile structure should have a spin-cutoff at about 3 h • The rotation period of (3599) Basov is confirmed to be P=2.157±0.037 h and a C-type asteroid by photometry and spectroscopy observations. • If (3599) Basov has a rubble-pile structure, it should not have such a short rotation period unless it has a very large cohesive force.

Fundamental physics and the absence of sub-millisecond pulsars

Context. Rapidly rotating neutron stars are an ideal laboratory to test models of matter at high densities. In particular, the maximum rotation frequency of a neutron star depends on the equation of state and can be used to test models of the interior. However, observations of the spin distribution of rapidly rotating neutron stars show evidence for a lack of stars spinning at frequencies higher than f ≈ 700 Hz, well below the predictions of theoretical equations of state. This has generally been taken as evidence of an additional spin-down torque operating in these systems, and it has been suggested that gravitational wave torques may be operating and be linked to a potentially observable signal. Aims. We aim to determine whether additional spin-down torques (possibly due to gravitational wave emission) are necessary, or if the observed limit of f ≈ 700 Hz could correspond to the Keplerian (mass-shedding) break-up frequency for the observed systems, and is simply a consequence of the currently unknown state of matter at high densities. Methods. Given our ignorance with regard to the true equation of state of matter above nuclear saturation densities, we make a minimal physical assumption and only demand causality, that is, that the speed of sound in the interior of the neutron star should be lower than or equal to the speed of light c. We then connected our causally limited equation of state to a realistic microphysical crustal equation of state for densities below nuclear saturation density. This produced a limiting model that gave the lowest possible maximum frequency, which we compared to observational constraints on neutron star masses and frequencies. We also compared our findings with the constraints on the tidal deformability obtained in the observations of the GW170817 event. Results. We rule out centrifugal breakup as the mechanism preventing pulsars from spinning faster than f ≈ 700 Hz, as the lowest breakup frequency allowed by our causal equation of state is f ≈ 1200 Hz. A low-frequency cutoff, around f ≈ 800 Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M ≈ 2 M⊙. This would have to be due either to selection effects, or possibly to a phase transition in the interior of the neutron star that leads to softening at high densities and a collapse to either a black hole or a hybrid star above M ≈ 2 M⊙. Such a scenario would, however, require a somewhat unrealistically stiff equation of state for hadronic matter, in tension with recent constraints obtained from gravitational wave observations of a neutron star merger.

Chaotic Zones around Rotating Small Bodies

Abstract Small bodies of the solar system, like asteroids, trans-Neptunian objects, cometary nuclei, and planetary satellites, with diameters smaller than 1000 km usually have irregular shapes, often resembling dumb-bells or contact binaries. The spinning of such a gravitating dumb-bell creates around it a zone of chaotic orbits. We determine its extent analytically and numerically. We find that the chaotic zone swells significantly if the rotation rate is decreased; in particular, the zone swells more than twice if the rotation rate is decreased 10 times with respect to the “centrifugal breakup” threshold. We illustrate the properties of the chaotic orbital zones in examples of the global orbital dynamics about asteroid 243 Ida (which has a moon, Dactyl, orbiting near the edge of the chaotic zone) and asteroid 25143 Itokawa.

Initial data for black hole–neutron star binaries, with rotating stars

The coalescence of a neutron star with a black hole is a primary science target of ground-based gravitational wave detectors. Constraining or measuring the neutron star spin directly from gravitational wave observations requires knowledge of the dependence of the emission properties of these systems on the neutron star spin. This paper lays foundations for this task, by developing a numerical method to construct initial data for black hole–neutron star binaries with arbitrary spin on the neutron star. We demonstrate the robustness of the code by constructing initial-data sets in large regions of the parameter space. In addition to varying the neutron star spin-magnitude and spin-direction, we also explore neutron star compactness, mass-ratio, black hole spin, and black hole spin-direction. Specifically, we are able to construct initial data sets with neutron stars spinning near centrifugal break-up, and with black hole spins as large as .

Melt film formation and disintegration during novel atomization process

Hybrid atomization is a new powder-making method and can produce economically very fine, clean, spherical tin alloy powders with average particle size about 10μm and narrow size distributions. The key concept of hybrid atomization is to control the liquid film formation on disk for fine powder production. Low-pressure gas atomization was utilized to promote the formation of a very thin stable liquid film before centrifugal breakup and give a better preparation for the final disintegration of melts. Besides the breakup ability of the rotating atomizer, the characteristics of liquid film on rotating disk affect the atomization mechanism and results remarkably. The main disintegration mode of melt is the breakup type of liquid film, which depends on the film instability and the atomization ability of the rotating disk. On the other hand, the mean powder size relates closely to the film thickness. The powder size distribution is mainly controlled by the atomization mode and the stability, flow type of liquid film on the rotating disk. A very thin, stable liquid film with long ligaments and a small pitch in LF mode results in very fine uniform tin alloy powders.

Nuclear-powered millisecond pulsars and the maximum spin frequency of neutron stars.

Millisecond pulsars are neutron stars that are thought to have been spun-up by mass accretion from a stellar companion. It is not known whether there is a natural brake for this process, or if it continues until the centrifugal breakup limit is reached at submillisecond periods. Many neutron stars that are accreting mass from a companion star exhibit thermonuclear X-ray bursts that last tens of seconds, caused by unstable nuclear burning on their surfaces. Millisecond-period brightness oscillations during bursts from ten neutron stars (as distinct from other rapid X-ray variability that is also observed) are thought to measure the stellar spin, but direct proof of a rotational origin has been lacking. Here we report the detection of burst oscillations at the known spin frequency of an accreting millisecond pulsar, and we show that these oscillations always have the same rotational phase. This firmly establishes burst oscillations as nuclear-powered pulsations tracing the spin of accreting neutron stars, corroborating earlier evidence. The distribution of spin frequencies of the 11 nuclear-powered pulsars cuts off well below the breakup frequency for most neutron-star models, supporting theoretical predictions that gravitational radiation losses can limit accretion torques in spinning up millisecond pulsars.

Magnetars in the Metagalaxy: An Origin for Ultra–High‐Energy Cosmic Rays in the Nearby Universe

I show that the relativistic winds of newly born magnetars (neutron stars with petagauss surface magnetic fields) with initial spin rates close to the centrifugal breakup limit, occurring in all normal galaxies with massive star formation, can provide a source of ultrarelativistic light ions with an E-1 injection spectrum, steepening to E-2 at higher energies, with an upper cutoff at 1021-1022 eV. Interactions with the cosmic microwave background yield a spectrum at the Earth that compares favorably with the spectrum of ultra-high-energy cosmic rays (UHECRs) observed at energies up to a few times 1020 eV. The fit to the observations suggests that ~5%-10% of the magnetars are born with rotation rates and voltages sufficiently high to allow the acceleration of the UHECR. The form the spectrum incident on the Earth takes depends sensitively on the mechanism and the magnitude of gravitational wave losses during the early spin-down of these neutron stars: pure electromagnetic spin-down (the E-1 injection spectrum) yields a GZK feature [a flattening of the E3J(E) spectrum] below 1020 eV, rather than a cutoff, while a moderate GZK cutoff appears if gravitational wave losses are strong enough to steepen the injection spectrum above 1020 eV. The flux above 1020 eV comes from magnetars in relatively nearby galaxies (D 100 EeV air showers, the model predicts gravitational wave strains ~3 × 10-21. Such bursts of gravitational radiation should correlate with bursts of ultra-high-energy particles. The Auger experiment should see bursts of particles with energy above 100 EeV every few years.

Tidal Spin‐up of Stars in Dense Stellar Cusps around Massive Black Holes

We show that main-sequence stars in dense stellar cusps around massive black holes are likely to rotate at a significant fraction of the centrifugal breakup velocity as a result of spin-up by hyperbolic tidal encounters. We use realistic stellar structure models to calculate analytically the tidal spin-up in soft encounters and extend these results to close and penetrating collisions using smoothed particle hydrodynamics simulations. We find that the spin-up effect falls off only slowly with distance from the black hole because the increased tidal coupling in slower collisions at larger distances compensates for the decrease in the stellar density. We apply our results to the stars near the massive black hole in the Galactic center. Over their lifetime, ~1 M☉ main-sequence stars in the inner 0.3 pc of the Galactic center are spun-up on average to ~10%-30% of the centrifugal breakup limit. Such rotation is ~20-60 times higher than is usual for such stars and may affect their subsequent evolution and their observed properties.

The Nucleus of Comet Hyakutake (C/1996 B2)

Infrared, optical, and radio continuum observations were made of the long-period comet C/Hyakutake 1996 B2 during its close approach to Earth in March 1996. Using these observations to characterize the comet's nucleus, we find an estimated nuclear radius of 2.4±0.5 km (1σ) from photometric resolution of the nucleus in the thermal infrared at 8–20 μm on 25 March 1996, no detectable optical nuclear emission above that of the coma on 19–23 March 1996, and a 3σ upper limit to the radius of 2.7 km (assuming an emissivity of 0.9) in the radio at 3.6 cm on 27 March 1996. The infrared color temperature of the nucleus was consistent with a 320-K blackbody, and assuming a 2.4-km radius, the maximum effective temperature at 3.6 cm was 230 K. We explain the optical nondetection of the nucleus as due to excess emission from a halo of small, cold, and high optical albedo dust particles surrounding the nucleus; such particles would have low emissivity in the infrared and radio. A surrounding halo of icy dust grains emitting water in addition to the nucleus accounts for the small nuclear size but large production rate of water from C/Hyakutake; otherwise an anomalously large fraction of the nuclear surface, nearly 100%, must be active. A fast rotation period of 6.30±0.03 h due to coma dust cross-sectional variations was found from optical and infrared imaging on March 20–23. The minimum bulk tensile strength required to stabilize the comet against centrifugal breakup due to this rotation, ∼103 dynes cm−2, is similar to that found for other comets.

Secondary fragmentation of comet Shoemaker-Levy 9 and the ramifications for the progenitor's breakup in July 1992

Comprehensive analysis of discrete events of secondary fragmentation leads to a conceptually new understanding of the process of disintegration of comet Shoemaker-Levy 9. We submit that the jovian tidal forces inflicted extensive cracks throughout the interior of the original nucleus but did not split it apart. The initial disruption was apparently accomplished by stresses exerted on the cracked object by its fast rotation during the early post-perijove period of time. We argue that this disruption was in fact a rapid sequence of episodes during July 1992 that gave birth to the 12 on-train, or primary, fragments: A, C, D, E, G, H, K, L, Q (later Q 1), R, S, and W. The discrete events of secondary fragmentation, which gave birth to the off-train fragments, are understood in this scenario as stochastic manifestations of the continuing process of progressive disintegration. Of the 13 off-train fragments considered, nine were secondary—B, F, G 2, M, N, P (later P 2 or P 2a), Q 2, U, and V—and four tertiary (J, P 1, P 2b, and T). The separation parameters of 11 off-train fragments were determined. The vectorial distribution of separation velocities of these fragments shows a strong concentration toward a great circle, unquestionably an effect of the approximately conserved angular momentum of the progenitor comet since the time of its initial disruption. Also apparent is their clumping (except for P 1) to a segment along the great circle, implying that the fragments were consistently released from one side of their parents, thus explaining for the first time why the off-train fragments preferentially appeared on one side of the nuclear train. In order to obtain a consistent solution, our model requires that the points of separation be on the antisolar side of the parent fragments, where thermal stresses are likely to enhance the effect of rotation. The episodes of secondary fragmentation are found to have occurred in a period of time from a few weeks to at least nine months after the close encounter with Jupiter in early July 1992, and the separation velocities ranged between 0.36 and 1.7 m s −1. The spin-axis position is determined to have been nearly in the jovicentric orbit plane, which rules out the Asphaug-Benz-Solem strengthless aggregate model as a plausible breakup hypothesis. Since the separation velocities are rotational in nature, they cannot substantially exceed the critical limit for centrifugal breakup and offer an estimate for the original nuclear dimensions. The comet's nucleus is found to have been approximately 10 km in diameter and spinning rapidly. With the exception of P 1, and apparently also P 2 and F, no nongravitational deceleration was detected in the motions of the off-train fragments. Serious doubts are cast on continuing appreciable activity of any of these fragments. Indeed, when it was necessary to introduce a deceleration into the equations of motion, the effect appears to have been due to the action of solar radiation pressure on the centroid of centimeter-sized particulates in the disintegrating condensations.

Simplified models of completely degenerate, differentially rotating stars

The properties of differentially rotating, completely degenerate sections of infinite cylinders are examined. Their construction is simple, with variables depending only on the radial cylindrical coordinate. They are found to possess important characteristics which qualitatively resemble much more complicated two-dimensional models of differentially rotating degenerate stars: (1) an analog of the Chandrasekhar limit; (2) a limit to uniform rotation imposed by centrifugal breakup; (3) massive, differentially rotating structures of moderate radius can be constructed; and (4) models obey the Solberg–Ho/iland criterion for stability of the rotation field and appear to be stable against inverse beta decay and general relativistic collapse. These characteristics combined with the simplicity of construction make these models useful in the study of the structure and evolution of differentially rotating stars.