Low Angular Momentum Research Articles

Parametrically narrow tetraquark states containing one heavy quark and one heavy antiquark

This paper focuses on tetraquarks containing one heavy quark and one heavy antiquark in the formal limit where the heavy quark masses go to infinity. It extends the theoretical framework developed for tetraquark containing two heavy quarks based on semi-classical analysis and the Born-Oppenheimer approximation. It is shown that for sufficiently small light quark masses, parametrically narrow $q\bar{q}'Q\bar{Q}$ tetraquarks must exist in the formal limit of arbitrarily large heavy quark masses. The analysis is model-independent; it requires no assumptions about the structure of the state or the mechanism of its decay beyond what can be deduced directly from QCD. The formal analysis here is only directly applicable to tetraquarks with large angular momentum and hence does not directly apply to experimentally observed tetraquark candidates. We also discuss the condition needed for a version of the analysis to apply for low angular momenta states. Whether this condition holds can be explored via lattice calculations. Current lattice calculations suggest that the condition is not met. If these preliminary calculations are confirmed, there are strong implications for the nature of the observed tetraquark resonances containing $\bar{c}c$ or $\bar{b}b$ pairs. It raises the possibility that the observed tetraquarks exist and are narrow not because the charm and bottom quarks are extremely heavy, but because they are sufficiently light.

Relativity and the periodic table.

The periodic table provides a deep unifying principle for understanding chemical behaviour by relating the properties of different elements. For those belonging to the fifth and earlier rows, the observations concerning these properties and their interrelationships acquired a sound theoretical basis by the understanding of electronic behaviour provided by non-relativistic quantum mechanics. However, for elements of high nuclear charge, such as occur in the sixth and higher rows of the periodic table, the systematic behaviour explained by non-relativistic quantum mechanics begins to fail. These problems are resolved by realizing that relativistic quantum mechanics is required in heavy elements where electrons velocities can reach significant fractions of the velocity of light. An essentially non-mathematical description of relativistic quantum mechanics explains how relativity modifies valence electron behaviour in heavy elements. The direct relativistic effect, arising from the relativistic increase of the electron mass with velocity, contracts orbitals of low angular momentum, increasing their binding energies. The indirect relativistic effect causes valence orbitals of high angular momentum to be more effectively screened as a result of the relativistic contraction of the core orbitals. In the alkali and alkaline earths, the s orbital contractions reverse the chemical trends on descending these groups, with heavy elements becoming less reactive. For valence d and f electrons, the indirect relativistic effect enhances the reductions in their binding energies on descending the periodic table. The d electrons in the heavier coinage metals thus become more chemically active, which causes these elements to exhibit higher oxidation states. The indirect effect on d orbitals causes the chemistries of the sixth-row transition elements to differ significantly from the very similar behaviours of the fourth and fifth-row transition series. The relativistic destabilization of f orbitals causes lanthanides to be chemically similar, forming mainly ionic compounds in oxidation state three, while allowing the earlier actinides to show a richer range of chemical behaviour with several higher oxidation states. For the 7p series of elements, relativity divides the non-relativistic p shell of three degenerate orbitals into one of much lower energy with the energies of the remaining two being substantially increased. These orbitals have angular shapes and spin distributions so different from those of the non-relativistic ones that the ability of the 7p elements to form covalent bonds is greatly inhibited. This article is part of the theme issue 'Mendeleev and the periodic table'.

Role of the quasifission yields in the multinucleon transfer reactions of Xe136+Pb208

The mass distribution in $^{136}\mathrm{Xe}+^{208}\mathrm{Pb}$ is investigated within the dinuclear system model. With the contribution of quasifission yields, the probability of all the fragments is conserved, and the mass distribution becomes wider with increasing the evolution time. The difference between including and excluding the contribution of quasifission yields is more obvious at a lower angular momentum. The cross sections, including quasifission yields in the region with mass less than the projectile and more than the target, are closer to the experimental data. The impact from the quasifission yields on the neutron-deficient isotopes is greater than the neutron-rich ones. The quasifission yields concentrate on the initial stage of evolution time, corresponding to a lower excitation energy. Considering the time-dependent excitation energy of the quasifission fragments produced within the interaction time, fewer neutrons are evaporated comparing to the case with the excitation energy at the interaction time.

Rapid filamentary accretion as the origin of extended thin discs

ABSTRACT Galactic outflows driven by stellar feedback are crucial for explaining the inefficiency of star formation in galaxies. Although strong feedback can promote the formation of galactic discs by limiting star formation at early times and removing low angular momentum (AM) gas, it is not understood how the same feedback can result in diverse objects such as elliptical galaxies or razor thin spiral galaxies. We investigate this problem using cosmological zoom-in simulations of two galaxies forming within 1012 M⊙ haloes with almost identical mass accretion histories and halo spin parameters. However, the two resulting galaxies end up with very different bulge-to-disc ratios at z = 0. At z > 1.5, the two galaxies feature a surface density of star formation ΣSFR ≃ 10 M⊙ yr−1 kpc−2, leading to strong outflows. After the last starburst episode, both galaxies feature a dramatic gaseous disc growth from 1 to 5 kpc during 1 Gyr, a decisive event we dub ‘the Grand Twirl’. After this event, the evolutionary tracks diverge strongly, with one galaxy ending up as a bulge-dominated galaxy, whereas the other ends up as a disc-dominated galaxy. The origins of this dichotomy are the AM of the accreted gas, and whether it adds constructively to the initial disc angular momentum. The build-up of this extended disc leads to a rapid lowering of ΣSFR by over two orders of magnitude with ΣSFR ≲ 0.1 M⊙ yr−1 kpc−2, in remarkable agreement with what is derived from Milky Way stellar populations. As a consequence, supernovae explosions are spread out and cannot launch galactic outflows anymore, allowing for the persistence of a thin, gently star-forming, extended disc.

ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377

Submillimetre and millimetre line and continuum observations are important in probing the morphology, column density, and dynamics of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their mechanical feedback. With very high-resolution (0.​​″02 × 0.​​″03 (2 × 3 pc)) ALMA 345 GHz observations of CO 3–2, HCO+ 4–3, vibrationally excited HCN 4–3 ν2 = 1f, and continuum we have studied the remarkable, extremely radio-quiet, molecular jet and wind of the lenticular galaxy NGC 1377. The outflow structure is resolved, revealing a 150 pc long, clumpy, high-velocity (∼600 km s−1), collimated molecular jet where the molecular emission is emerging from the spine of the jet with an average diameter of 3–7 pc. The jet widens to 10–15 pc about 25 pc from the centre, which is possibly due to jet-wind interactions. A narrow-angle (50°–70°), misaligned and rotating molecular wind surrounds the jet, and both are enveloped by a larger-scale CO-emitting structure at near-systemic velocity. The jet and narrow wind have steep radial gas excitation gradients and appear turbulent with high gas dispersion (σ > 40 km s−1). The jet shows velocity reversals that we propose are caused by precession, or more episodic directional changes. We discuss the mechanisms powering the outflow, and we find that an important process for the molecular jet and narrow wind is likely magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r ∼ 2 pc dust structure with a high inferred molecular column density N(H2) ≃1.8 × 1024 cm−2 is detected in continuum and also shows compact emission from vibrationally excited HCN. The nuclear dust emission is hot (Td > 180 K) and its luminosity is likely powered by a buried AGN. The lopsided structure appears to be a warped disk, which is responsible for a significant part of the nuclear obscuration and possibly formed as a result of uneven gas inflows. The dynamical mass inside r = 1.4 pc is estimated to 9−3+2 × 106 M⊙, implying that the supermassive black hole (SMBH) has a high mass with respect to the stellar velocity dispersion of NGC 1377. We suggest that the SMBH of NGC 1377 is currently in a state of moderate growth, at the end of a more intense phase of accretion and also evolving from a state of more extreme nuclear obscuration. The nuclear growth may be fuelled by low-angular momentum gas inflowing from the gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic outflows and central accretion could explain why there is still a significant reservoir of molecular gas in this ageing, lenticular galaxy. A feedback-loop would be an effective process in growing the nuclear SMBH and thus would constitute an important phase in the evolution of NGC 1377. This also invites new questions as to SMBH growth processes in obscured, dusty galaxies.

Study of relativistic accretion flow in Kerr-Taub-NUT spacetime

We study the properties of the relativistic, steady, axisymmetric, low angular momentum, inviscid, advective, geometrically thin accretion flow in a Kerr-Taub-NUT (KTN) spacetime which is characterized by the Kerr parameter ($a_{\rm k}$) and NUT parameter ($n$). Depending on $a_{\rm k}$ and $n$ values, KTN spacetime represents either a black or a naked singularity. We solve the governing equations that describe the relativistic accretion flow in KTN spacetime and obtain all possible global transonic accretion solutions around KTN black hole in terms of the energy $({\cal E})$ and angular momentum $(\lambda)$ of the flow. We identify the region of the parameter space in $\lambda-{\cal E}$ plane that admits the flow to possess multiple critical points for KTN black hole. We examine the modification of the parameter space due to $a_{\rm k}$ and $n$ and find that the role of $a_{\rm k}$ and $n$ in determining the parameter space is opposite to each other. This clearly indicates that the NUT parameter $n$ effectively mitigates the effect of black hole rotation in deciding the accretion flow structure. Further, we calculate the maximum disc luminosity ($L_{\rm max}$) corresponding to the accretion solutions around the KTN black hole and for a given set of $a_{\rm k}$ and $n$. In addition, we also investigate all possible flow topologies around the naked singularity and find that there exists a region around the naked singularity which remains inaccessible to the flow. We study the critical point properties for naked singularities and find that the flow possesses maximum of four critical points. Finally, we obtain the parameter space for multiple critical points for naked singularity and find that parameter space is shrunk and shifted to lower $\lambda$ and higher ${\cal E}$ side as $a_{\rm k}$ is increased which ultimately disappears.

Emergence of Haldane Pseudo-Potentials in Systems with Short-Range Interactions

In the setting of the fractional quantum Hall effect we study the effects of strong, repulsive two-body interaction potentials of short range. We prove that Haldane’s pseudo-potential operators, including their pre-factors, emerge as mathematically rigorous limits of such interactions when the range of the potential tends to zero while its strength tends to infinity. In a common approach the interaction potential is expanded in angular momentum eigenstates in the lowest Landau level, which amounts to taking the pre-factors to be the moments of the potential. Such a procedure is not appropriate for very strong interactions, however, in particular not in the case of hard spheres. We derive the formulas valid in the short-range case, which involve the scattering lengths of the interaction potential in different angular momentum channels rather than its moments. Our results hold for bosons and fermions alike and generalize previous results in [6], which apply to bosons in the lowest angular momentum channel. Our main theorem asserts the convergence in a norm-resolvent sense of the Hamiltonian on the whole Hilbert space, after appropriate energy scalings, to Hamiltonians with contact interactions in the lowest Landau level.

The rise of active galactic nuclei in the galaxy evolution and assembly semi-analytic model

ABSTRACT We present a new implementation of the GAlaxy Evolution and Assembly (gaea) semi-analytic model, that features an improved modelling of the process of cold gas accretion on to supermassive black hole (SMBHs), derived from both analytic arguments and high-resolution simulations. We consider different scenarios for the loss of angular momentum required for the available cold gas to be accreted on to the central SMBHs, and we compare different combinations of triggering mechanisms, including galaxy mergers and disc instabilities in star-forming discs. We compare our predictions with the luminosity function (LF) observed for active galactic nuclei (AGNs) and we confirm that a non-instantaneous accretion time-scale (either in the form of a low-angular momentum reservoir or as an assumed light-curve evolution) is needed in order to reproduce the measured evolution of the AGN-LF and the so-called AGN-downsizing trend. Moreover, we also study the impact of AGN feedback, in the form of AGN-driven outflows, on the SF properties of model galaxies, using prescriptions derived both from empirical studies and from numerical experiments. We show that AGN-driven outflows are effective in suppressing the residual star formation rate in massive galaxies (>1011 M⊙) without changing their overall assembly history. These winds also affect the SFR of lower mass galaxies, resulting in a too large fraction of passive galaxies at <1010 M⊙. Finally, we study the Eddington ratio distribution as a function of SMBH mass, showing that only objects more massive than 108 M⊙ are already in a self-regulated state as inferred from observations.

The Angular Momentum of the Circumgalactic Medium in the TNG100 Simulation

Abstract We present an analysis of the angular momentum content of the circumgalactic medium (CGM) using TNG100, one of the flagship runs of the IllustrisTNG project. We focus on Milky Way–mass halos (∼1012 M ⊙) at z = 0 but also analyze other masses and redshifts up to z = 5. We find that the CGM angular momentum properties are strongly correlated with the stellar angular momentum of the corresponding galaxy: the CGM surrounding high-angular momentum galaxies has a systematically higher angular momentum and is better aligned to the rotational axis of the galaxy itself than the CGM surrounding low-angular momentum galaxies. Both the hot and cold phases of the CGM show this dichotomy, though it is stronger for colder gas. The CGM of high-angular momentum galaxies is characterized by a large wedge of cold gas with rotational velocities at least ∼1/2 of the halo’s virial velocity, extending out to ∼1/2 of the virial radius, and by biconical polar regions dominated by radial velocities suggestive of galactic fountains; both of these features are absent from the CGM of low-angular momentum galaxies. These conclusions are general to halo masses ≲1012 M ⊙ and for z ≲ 2, but they do not apply for more massive halos or at the highest redshift studied. By comparing simulations run with alterations to the fiducial feedback model, we identify the better alignment of the CGM to high-angular momentum galaxies as a feedback-independent effect and the galactic winds as a dominant influence on the CGM’s angular momentum.

Stellar angular momentum distribution linked to galaxy morphology

ABSTRACT We study the spatially resolved stellar specific angular momentum j* in a high-quality sample of 24 Calar Alto Legacy Integral Field Area galaxies covering a broad range of visual morphology, accounting for stellar velocity and velocity dispersion. The shape of the spaxelwise probability density function of normalized s = j*/j*mean, PDF(s), deviates significantly from the near-universal initial distribution expected of baryons in a dark matter halo and can be explained by the expected baryonic effects in galaxy formation that remove and redistribute angular momentum. Further we find that the observed shape of the PDF(s) correlates significantly with photometric morphology, where late-type galaxies have a PDF(s) that is similar to a normal distribution, whereas early types have a strongly skewed PDF(s) resulting from an excess of low-angular momentum material. Galaxies that are known to host pseudo-bulges (bulge Sérsic index nb < 2.2) tend to have less skewed bulge PDF(s), with skewness (b1rb) ≲ 0.8. The PDF(s) encodes both kinematic and photometric information and appears to be a robust tracer of morphology. Its use is motivated by the desire to move away from traditional component-based classifications which are subject to observer bias, to classification on a galaxy’s fundamental (stellar mass and angular momentum) properties. In future, PDF(s) may also be useful as a kinematic decomposition tool.

Dressed metric predictions revisited

It was recently shown that the volume operator of loop quantum cosmology (LQC) and all its positive powers are ill-defined on physical states. In this paper, we investigate how it effects predictions of cosmic microwave background (CMB) power spectra obtained within dressed metric approach for which expectations values of â are the key element. We find that almost every step in the procedure is ill-defined and relies heavily upon a (seemingly premature) numerical truncation. Thus, it suggests that more care is needed in making predictions regarding pre-inflationary physics. We propose a new scheme which contains only well-defined quantities. The surprising agreement of the hitherto models with observational data, especially at low angular momenta l is explained.

Different modes of star formation – II. Gas accretion phase of initially subcritical star-forming clouds

ABSTRACT The accretion phase of star formation is investigated in magnetically dominated clouds that have an initial subcritical mass-to-flux ratio. We employ non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and ohmic dissipation. During the early prestellar phase, the mass-to-flux ratio rises towards the critical value for collapse, and during this time the angular momentum of the cloud core is reduced significantly by magnetic braking. Once a protostar is formed in the core, the accretion phase is characterized by the presence of a small amount of angular momentum but a large amount of magnetic flux in the near-protostellar environment. The low angular momentum leads to a very small (or even non-existent) disc and weak outflow, while the large magnetic flux can lead to an interchange instability that rapidly removes flux from the central region. The effective magnetic braking in the early collapse phase can even lead to a counterrotating disc and outflow, in which the rotation direction of the disc and outflow is opposite to that of the infalling envelope. The solutions with a counterrotating disc, tiny disc, or non-existent disc (direct collapse) are unique outcomes that are realized in collapse from magnetically dominated clouds with an initial subcritical mass-to-flux ratio.

The Splash without a Merger

Abstract The Milky Way’s progenitor experienced several merger events that left their imprints on the stellar halo, including the Gaia-Sausage/Enceladus. Recently, it has been proposed that this event perturbed the proto-disk and gave rise to a metal-rich ([Fe/H] > −1), low angular momentum (v ϕ < 100 km s−1) stellar population. These stars have dynamical and chemical properties different from the accreted stellar halo, but are continuous with the canonical thick disk. In this Letter, we use a hydrodynamical simulation of an isolated galaxy that develops clumps that produce a bimodal thin+thick disk chemistry to explore whether it forms such a population. We demonstrate that clump scattering forms a metal-rich, low angular momentum population, without the need for a major merger. We show that, in the simulation, these stars have chemistry, kinematics, and density distribution in good agreement with those in the Milky Way.

Effects of Magnetic Field Loops on the Dynamics of Advective Accretion Flows and Jets around a Schwarzschild Black Hole

Abstract Magnetic fields advected along with low angular momentum accretion flows predominantly become toroidal owing to the strong azimuthal velocity close to a black hole. We study self-consistently the movements of these flux tubes inside an advective disk and how they dynamically influence the flow. We find that the centrifugal barrier slows down the radial motion of the flux tubes. In this case, the large magnetic flux tubes with a significant drag force escape along the vertical axis owing to buoyancy. Magnetic pressure rises close to the black hole and, together with the centrifugal force, combats gravity. The tug-of-war among these forces causes the centrifugal-pressure-supported shock to oscillate radially. We study the effects of successive injection of flux tubes and find how the flux tube could be trapped inside the disk in regions of highest entropy. Most interestingly, the shock wave remains at its average location and is not destroyed. We show that the toroidal field loops contribute significantly to collimate and accelerate the outflows from the centrifugal barrier and suggest that this mechanism is a way to collimate and accelerate jets.

Greybody factor for a rotating Bardeen black hole

In this paper, we formulate an analytical expression of the greybody factor in the context of a rotating Bardeen black hole which is valid in the low energy and low angular momentum region. Primarily, we analyze the profile of the effective potential which originates the absorption probability. We then derive two asymptotic solutions by solving the radial part of the Klein-Gordon equation in two different regions, namely, black hole and far-field horizons. We match these solutions smoothly to an intermediate regime to extend our results over the whole radial coordinate. In order to elaborate the significance of the analytical solution, we compute the energy emission rate and absorption cross-section for the massless scalar field. It is found that the rotation parameter increases the emission rate of scalar field particles while the orbital angular momentum minimizes the emission process.

Capacity of turbulent ocean links with carrier Bessel-Gaussian localized vortex waves.

Based on the power spectrum of the index fluctuation with the outer scale of seawater turbulence, we develop the channel capacity of oceanic turbulence links with carrier Bessel-Gaussian vortex localized waves. By this capacity model, we investigate the influences of seawater turbulence and carrier parameters on the channel capacity. The results show that a higher rate of dissipation of kinetic energy per unit mass of fluid, larger inner scale, or lower dissipation rate of the mean-squared temperature causes the higher channel capacity; the Bessel-Gaussian localized vortex wave with a larger source transverse size, smaller Bessel cone angle, lower orbital angular momentum quantum number, or broader initial half-pulse width has stronger resistance to oceanic turbulent perturbation. This work provides a theoretical basis for realizing high-capacity oceanic optical communication with carrier Bessel-Gaussian vortex localized waves.

Gas accretion and galactic fountain flows in the Auriga cosmological simulations: angular momentum and metal redistribution

ABSTRACT Using a set of 15 high-resolution magnetohydrodynamic cosmological simulations of Milky Way formation, we investigate the origin of the baryonic material found in stars at redshift zero. We find that roughly half of this material originates from subhalo/satellite systems and half is smoothly accreted from the intergalactic medium. About $90 {{\ \rm per\ cent}}$ of all material has been ejected and re-accreted in galactic winds at least once. The vast majority of smoothly accreted gas enters into a galactic fountain that extends to a median galactocentric distance of ∼20 kpc with a median recycling time-scale of ∼500 Myr. We demonstrate that, in most cases, galactic fountains acquire angular momentum via mixing of low angular momentum, wind-recycled gas with high angular momentum gas in the circumgalactic medium (CGM). Prograde mergers boost this activity by helping to align the disc and CGM rotation axes, whereas retrograde mergers cause the fountain to lose angular momentum. Fountain flows that promote angular momentum growth are conducive to smooth evolution on tracks quasi-parallel to the disc sequence of the stellar mass-specific angular momentum plane, whereas retrograde minor mergers, major mergers, and bar-driven secular evolution move galaxies towards the bulge sequence. Finally, we demonstrate that fountain flows act to flatten and narrow the radial metallicity gradient and metallicity dispersion of disc stars, respectively. Thus, the evolution of galactic fountains depends strongly on the cosmological merger history and is crucial for the chemodynamical evolution of Milky-Way-sized disc galaxies.

Disentangling the Arcturus stream

Context. The Arcturus stream is an over-density of stars in velocity space and its origin has been much debated recently without any clear conclusion. The (classical) dissolved open cluster origin is essentially refuted; instead the discussions try to distinguish between an accretion, a resonant, or an external-perturbation origin for the stream. As kinematic structures are observational footprints of ongoing and past dynamical processes in disc galaxies, resolving the nature of the Arcturus stream may provide clues to the formation history of the Milky Way and its stellar populations. Aims. We aim to characterise the kinematical and chemical properties of the Arcturus stream in order to resolve its origin. Methods. The space velocities, angular momenta, and actions for a sample of more than 5.8 million stars, composed from Gaia DR2 were analysed with a wavelet transform method to characterise kinematic over-densities in the Galactic disc. The kinematic characteristics of each identified group is used to select possible members of the groups from the GALAH and APOGEE spectroscopic surveys to further study and constrain their chemical properties. Results. In the velocity and angular momentum spaces the already known Sirius, Pleiades, Hyades, Hercules, AF06, Arcturus and KFR08 streams are clearly identified. The Hercules stream appears to be a mixture of thin and thick disc stars. The Arcturus stream, as well as the AF06 and KFR08 streams, are high-velocity and low-angular momentum structures with chemical compositions similar to the thick disc. These three groups extend further from the Galactic plane compared to the Hercules stream. The detections of all the groups were spaced by approximately 20 − 30 km s−1 in azimuthal velocity. Conclusions. A wide spread of chemical abundances within the Arcturus stream indicates that the group is not a dissolved open cluster. Instead the Arcturus stream, together with the AF06 and KFR08 streams, are more likely to be part of a phase-space wave, that could have been caused by a merger event. This conclusion is based on that the different structures are detected in steps of 20 − 30 km s−1 in azimuthal velocity, that the kinematic and chemical features are different from what is expected for bar-originated structures, and that the higher-velocity streams extend further from the disc than bar-originated structures.

Influence of geometrical configuration on low angular momentum relativistic accretion around rotating black holes

This work illustrates how the formation of energy-preserving shocks for polytropic accretion and temperature-preserving shocks for isothermal accretion are influenced by various geometrical configurations of general relativistic, axisymmetric, low-angular-momentum flow in the Kerr metric. Relevant pre- and post-shock states of the accreting fluid, both dynamical and thermodynamic, have been studied comprehensively. Self-gravitational back-reaction on the metric has not been considered in the present context. An elegant eigenvalue-based analytical method has been introduced to provide qualitative descriptions of the phase-orbits corresponding to stationary transonic accretion solutions, without resorting to involved numerical schemes. Effort has been made to understand how the weakly-rotating flow behaves in close proximity of the event horizon and how such `quasi-terminal' quantities are influenced by the black hole spin for different matter geometries. Our main purpose is thus to mathematically demonstrate that for non-self-gravitating accretion, separate matter geometries, in addition to the corresponding space-time geometry, control various shock-induced phenomena observed within black hole accretion discs. This work is expected to reveal how such phenomena observed near the horizon depend on physical environment of the source harbouring a supermassive black hole at its centre. It is also expected to unfold correspondences between the dependence of accretion-related parameters on flow geometries and on black hole spin. Temperature-preserving shocks in isothermal accretion may appear bright as substantial amount of rest-mass energy of the infalling matter gets dissipated at the shock surface, and the prompt removal of such energy to maintain isothermality may power the X-ray/IR flares emitted from our Galactic centre.

Population control of Mars Trojans by the Yarkovsky & YORP effects

We explore the hypothesis that the population of Martian Trojans is the result of a balance between the production of new asteroids (“YORPlets”) through the YORP effect and their eventual escape from the Trojan clouds through Yarkovsky-driven orbital evolution. Our principal observables are: (5261) Eureka, its family of 8 asteroids and the family-less Trojans (101429) 1998 VF31 & (121514) 1999 UJ7. We model the population evolution as a birth-death random process and assume it is in a steady state. We then simulate the discovery of Trojans to-date and find that family members of 101429 and 121514, if they exist, are intrinsically more difficult to detect than Eureka's. Their non-discovery can be used as evidence of their non-existence only under the assumption that their brightness relative to the parent asteroid is similar to that in the Eureka family. To find out how efficiently Mars Trojans are lost from the Trojan clouds due to the Yarkovsky effect, we carry out dynamical simulations of test particles originating from these parent bodies. We find that objects originating from Eureka and 121514 begin escaping after ~1 Gyr, but that those from 101429 are already lost by that time, probably due to that asteroid's proximity to an eccentricity-type secular resonance within Mars's co-orbital region. This is the likely cause behind the absence of Trojans in the orbital vicinity of 101429. In contrast, the solitary status of 121514 points to an intrinsic inability of the asteroid to produce YORPlets during the most recent ~20% of the solar system's history, a finding potentially related to 121514’s present, low angular momentum rotational state, unless the Eureka family formed rapidly during a single fission event.