ABSTRACT We explore full/partial tidal disruption events (TDEs) of stars/planets by stellar compact objects (black holes (BHs) or neutron stars (NSs)), which we term micro-TDEs. Disruption of a ...star/planet with mass M may lead to the formation of a debris disk around the BH/NS. Efficient accretion of a fraction of the debris may then give rise to bright, energetic, long (103-104 s), X-ray/gamma-ray flares, with total energies of up to erg, possibly resembling ultra-long gamma-ray bursts (GRBs)/X-ray flashes (XRFs). The energy of such flares depends on the poorly constrained accretion processes. Significantly fainter flares might be produced if most of the disk mass is blown away through strong outflows. We suggest three dynamical origins for such disruptions. In the first, a star/planet is tidally disrupted following a close random encounter with a BH/NS in a dense cluster. We estimate the BH (NS) micro-TDE rates from this scenario to be a few (a few ) per Milky Way galaxy. Another scenario involves the interaction of wide companions due to perturbations by stars in the field, likely producing comparable but lower rates. Finally, a third scenario involves a BH/NS that gains a natal velocity kick at birth, leading to a close encounter with a binary companion and the tidal disruption of that companion. Such events could be associated with a supernova, or even with a preceding GRB/XRF event, and would likely occur hours to days after the prompt explosion; the rates of such events could be larger than those obtained from the other scenarios, depending on the preceding complex binary stellar evolution.
V1309 Sco—UNDERSTANDING A MERGER NANDEZ, J L A; Ivanova, N; LOMBARDI, J C
The Astrophysical journal,
05/2014, Letnik:
786, Številka:
1
Journal Article
Recenzirano
Odprti dostop
One of the two outcomes of a common envelope (CE) event is a merger of the two stars. To date, the best known case of a binary merger is the V1309 Sco outburst, where the orbital period was known and ...observed to decay up to the outburst. Using the hydrodynamical code StarSmasher, we study in detail which characteristics of the progenitor binary affect the outburst and produce the best match with observations. We have developed a set of tools in order to quantify any CE event. We consider binaries consisting of a 1.52 M sub(middot in circle) giant and a 0.16 M sub(middot in circle) companion with P sub(orb) ~ 1.4 days, varying the nature of the companion and its synchronization. We show that all considered progenitor binaries evolve toward the merger primarily because of Darwin instability. The merger is accompanied by mass ejection that proceeds in several separate mass outbursts and takes away a few percent of the donor mass. This very small mass, nonetheless, is important as it is not only sufficient to explain the observed light curve, but it also carries away up to one-third of both the initial total angular momentum and initial orbital energy. We find that all synchronized systems experience L sub(2) mass loss that operates during just a few days prior to the merger and produces ring-shaped ejecta. The formed star is always a strongly heated radiative star that differentially rotates. We conclude that the case of a synchronized binary with a main-sequence companion gives the best match with observations of V1309 Sco.
Autonomic nervous system (ANS) has been extensively explored in obstructive sleep apnea (OSA).
Autonomic alterations in these patients have been described by means of several methods, evaluating ANS ...function both directly with microneurography and indirectly through baroreflex sensitivity (BRS, by the sequence method or the cross-spectral approach), heart rate variability analysis (HRV, both in the time and frequency domain) during sleep and wake, or conventional laboratory tests, including cold pressor test, hand grip test or measurement of urinary cathecolamine excretion.
Several studies in OSA patients have shown ANS alterations, in particular sympathetic overactivity, both acutely during apnea events and chronically during the daytime, being both also involved in cardiovascular consequences of sleep disordered breathing.
The association between OSA and sympathetic dysregulation suggests a dose response relationship between OSA severity and the degree of sympathetic overactivity and this association seems to be reversible as the treatment of OSA is implemented.
Additionally ANS is involved in regulating visceral and humoral functions to maintain the body homeostasis and in reaction and adaptation to external and internal stressor stimuli.
However, the vast majority of studies have focussed on cardiovascular alterations, which are easier to measure, somewhat neglecting the other functions regulated by ANS.
More evidence is therefore needed to better characterize the impact that sleep disorder breathing may have on ANS both in the short and long term.
Identification of the Long-Sought Common-Envelope Events Ivanova, N.; Justham, S.; Nandez, J. L. Avendano ...
Science (American Association for the Advancement of Science),
01/2013, Letnik:
339, Številka:
6118
Journal Article
Recenzirano
Odprti dostop
Common-envelope events (CEEs), during which two stars temporarily orbit within a shared envelope, are believed to be vital for the formation of a wide range of close binaries. For decades, the only ...evidence that CEEs actually occur has been indirect, based on the existence of systems that could not be otherwise explained. Here we propose a direct observational signature of CEEs arising from a physical model where emission from matter ejected in a CEE is controlled by a recombination front as the matter cools. The natural range of time scales and energies from this model, as well as the expected colors, light-curve shapes, ejection velocities, and event rate, match those of a recently recognized class of red transient outbursts.
Abstract
Recent analyses have shown that close encounters between stars and stellar black holes occur frequently in dense star clusters. Depending upon the distance at closest approach, these ...interactions can lead to dissipating encounters such as tidal captures and disruptions, or direct physical collisions, all of which may be accompanied by bright electromagnetic transients. In this study, we perform a wide range of hydrodynamic simulations of close encounters between black holes and main-sequence stars that collectively cover the parameter space of interest, and we identify and classify the various possible outcomes. In the case of nearly head-on collisions, the star is completely disrupted with roughly half of the stellar material becoming bound to the black hole. For more distant encounters near the classical tidal-disruption radius, the star is only partially disrupted on the first pericenter passage. Depending upon the interaction details, the partially disrupted stellar remnant may be tidally captured by the black hole or become unbound (in some cases, receiving a sufficiently large impulsive kick from asymmetric mass loss to be ejected from its host cluster). In the former case, the star will undergo additional pericenter passages before ultimately being disrupted fully. Based on the properties of the material bound to the black hole at the end of our simulations (in particular, the total bound mass and angular momentum), we comment upon the expected accretion process and associated electromagnetic signatures that are likely to result.
In this Letter, we investigate the role of recombination energy during a common envelope event. We confirm that taking this energy into account helps to avoid the formation of the circumbinary ...envelope commonly found in previous studies. For the first time, we can model a complete common envelope event, with a clean compact double white dwarf binary system formed at the end. The resulting binary orbit is almost perfectly circular. In addition to considering recombination energy, we also show that between 1/4 and 1/2 of the released orbital energy is taken away by the ejected material. We apply this new method to the case of the double white dwarf system WD 1101+364, and we find that the progenitor system at the start of the common envelope event consisted of an ∼1.5 M⊙ red giant star in an ∼30 d orbit with a white dwarf companion.
The onset of runaway stellar collisions in young star clusters is more likely to initiate with an encounter between a binary and a third star than between two single stars. Using the initial ...conditions of such three-star encounters from direct N-body simulations, we model the resulting interaction by means of smoothed particle hydrodynamics (SPH). Our code implements new equations of motion that allow for efficient use of non-equal mass particles and is capable of evolving contact binaries for thousands of orbits, if not indefinitely. We find that, in the majority of the cases considered, all three stars merge together. In addition, we compare our SPH calculations against those of the sticky-sphere approximation. If one is not concerned with mass loss, then the sticky sphere approach gives the correct qualitative outcome in approximately 75 per cent of the cases considered. Among those cases in which the sticky-sphere algorithm identifies only two particular stars to collide, the hydrodynamic calculations find the same qualitative outcome in about half of the instances. If the sticky-sphere approach determines that all three stars merge, then the hydrodynamic simulations invariably agree. However, in such three-star mergers, the hydrodynamic simulations reveal that: (i) mass lost as ejecta can be a considerable fraction of the total mass in the system (up to ∼25 per cent); (ii) due to asymmetric mass loss, the collision product can sometimes receive a kick velocity that exceeds 10 km s−1, large enough to allow the collision product to escape the core of the cluster; and (iii) the energy of the ejected matter can be large enough (up to ∼3 × 1050 erg) to remove or disturb the inter cluster gas appreciably.
During the merger of a black hole and a neutron star, baryonic mass can become unbound from the system. Because the ejected material is extremely neutron-rich, the r-process rapidly synthesizes heavy ...nuclides as the material expands and cools. In this work, we map general relativistic models of black hole-neutron star mergers into a Newtonian smoothed particle hydrodynamics (SPH) code and follow the evolution of the thermodynamics and morphology of the ejecta until the outflows become homologous. We investigate how the subsequent evolution depends on our mapping procedure and find that the results are robust. Using thermodynamic histories from the SPH particles, we then calculate the expected nucleosynthesis in these outflows while varying the level of neutrino irradiation coming from the post-merger accretion disc. We find that the ejected material robustly produces r-process nucleosynthesis even for unrealistically high neutrino luminosities, due to the rapid velocities of the outflow. None the less, we find that neutrinos can have an impact on the detailed pattern of the r-process nucleosynthesis. Electron neutrinos are captured by neutrons to produce protons while neutron capture is occurring. The produced protons rapidly form low-mass seed nuclei for the r-process. These low-mass seeds are eventually incorporated into the first r-process peak at A ~ 78. We consider the mechanism of this process in detail and discuss if it can impact galactic chemical evolution of the first peak r-process nuclei.
Abstract
We study close encounters of a 1
M
⊙
middle-age main-sequence star (modeled using MESA) with massive black holes through hydrodynamic simulations, and explore in particular the dependence of ...the outcomes on the black hole mass. We consider here black holes in the intermediate-mass range,
M
BH
= 100–10
4
M
⊙
. Possible outcomes vary from a small tidal perturbation for weak encounters all the way to partial or full disruption for stronger encounters. We find that stronger encounters lead to increased mass loss at the first pericenter passage, in many cases ejecting the partially disrupted star on an unbound orbit. For encounters that initially produce a bound system, with only partial stripping of the star, the fraction of mass stripped from the star increases with each subsequent pericenter passage and a stellar remnant of finite mass is ultimately ejected in all cases. The critical penetration depth that separates bound and unbound remnants has a dependence on the black hole mass when
M
BH
≲ 10
3
M
⊙
. We also find that the number of successive close passages before ejection decreases as we go from the stellar-mass black hole to the intermediate-mass black hole regime. For instance, after an initial encounter right at the classical tidal disruption limit, a 1
M
⊙
star undergoes 16 (5) pericenter passages before ejection from a 10
M
⊙
(100
M
⊙
) black hole. Observations of periodic flares from these repeated close passages could in principle indicate signatures of a partial tidal disruption event.
Background
Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent.
Methods
Six scientific Italian societies entitled to cure thyroid ...cancer patients (the Italian Thyroid Association, the Medical Endocrinology Association, the Italian Society of Endocrinology, the Italian Association of Nuclear Medicine and Molecular Imaging, the Italian Society of Unified Endocrine Surgery and the Italian Society of Anatomic Pathology and Diagnostic Cytology) felt the need to develop a consensus report based on significant scientific advances occurred in the field.
Objective
The document includes recommendations regarding initial evaluation of thyroid nodules, clinical and ultrasound criteria for fine-needle aspiration biopsy, initial management of thyroid cancer including staging and risk assessment, surgical management, radioiodine remnant ablation, and levothyroxine therapy, short-term and long-term follow-up strategies, and management of recurrent and metastatic disease. The objective of this consensus is to inform clinicians, patients, researchers, and health policy makers about the best strategies (and their limitations) relating to the diagnosis and treatment of differentiated thyroid cancer.
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