Escape Velocity Research Articles

Determination of the escape velocity of the Milky Way using a halo sample selected based on proper motion

Context. The Gaia mission has provided the largest catalogue ever of sources with tangential velocity information. However, it is difficult to use this catalogue for dynamical studies because most of the stars lack line-of-sight velocity measurements. Recently, we presented a selection of ∼107 halo stars with accurate distances that were selected based on their photometry and proper motions. Aims. Using this sample, we model the tail of the velocity distribution in the stellar halo locally and as a function of distance. Our goal is to measure the escape velocity, and based on this, to constrain the mass of our Galaxy. Methods. We fitted the tail of the velocity distribution with a power-law distribution, a commonly used approach that has long been established. For the first time, we used tangential velocities that were accurately measured for an unprecedented number of halo stars to estimate the escape velocity. Results. In the solar neighbourhood, we obtain a very precise estimate of the escape velocity, which is 497−8+8 km s−1. This estimate is most likely biased low, our best guess is by 10%. As a result, the true escape velocity is most likely closer to 550 km s−1. The escape velocity directly constrains the total mass of the Milky Way. To find the best-fitting halo mass and concentration parameter, we adjusted the dark (spherical Navarro-Frenk-White) halo of a realistic Milky Way potential while keeping the circular velocity at the solar radius fixed at vc(R⊙) = 232.8 km s−1. The resulting halo parameters are M200+10% = 1.11−0.07+0.08 · 1012 M⊙, and the concentration parameter is c+10% = 11.8−0.3+0.3, where we use the explicit notation to indicate that they are corrected for the 10% bias. The slope of the escape velocity with galactocentric distance is as expected in the inner Galaxy based on Milky Way models. Curiously, we find a disagreement beyond the solar radius where the estimated escape velocity is higher than at the solar radius. This result is likely an effect of a change in the shape of the velocity distribution and could be related to the presence of velocity clumps. A tentative analysis of the escape velocity as a function of (R, z) shows that the slope is shallower than expected for a spherical halo when standard values are used for the characteristic parameters describing the galactic disc.

Kiloparsec view of a typical star-forming galaxy when the Universe was ∼1 Gyr old

We present new Atacama Large Millimeter/Submillimeter Array observations of the [C II] 158 μm transition and the dust continuum in HZ4, a typical star-forming galaxy when the Universe was only ∼1 Gyr old (z ≈ 5.5). Our high ≈0.3″ spatial resolution allows us to study the relationships between [C II] line emission, star formation rate, and far-infrared emission on spatial scales of ∼2 kpc. In the central ∼4 kpc of HZ4, the [C II]/FIR is ∼3 × 10−3 on global scales as well as on spatially resolved scales of ∼2 kpc, comparable to the ratio observed in local moderate starburst galaxies such as M 82 or M 83. For the first time in an individual normal galaxy at this redshift, we find evidence for outflowing gas from the central star-forming region in the direction of the minor axis of the galaxy. The projected velocity of the outflow is ∼400 km s−1, and the neutral gas-mass outflow rate is ∼3 − 6 times higher than the star formation rate in the central region. Finally, we detect a diffuse component of [C II] emission, or [C II] halo, that extends beyond the star-forming disk and has a diameter of ∼12 kpc. The outflow, which has a velocity approximately half of the escape velocity of the system, most likely partly fuels the [C II] extended emission. Together with the kinematic analysis of HZ4 (presented in a forthcoming paper), the analysis supports the hypothesis that HZ4 is a typical star-forming disk at z ∼ 5 with interstellar medium conditions similar to present-day galaxies forming stars at a similar level, driving a galactic outflow that may already play a role in its evolution.

Compact Starburst Galaxies with Fast Outflows: Central Escape Velocities and Stellar Mass Surface Densities from Multiband Hubble Space Telescope Imaging

Abstract We present multiband Hubble Space Telescope imaging that spans rest-frame near-ultraviolet through near-infrared wavelengths ( –1.1 μm) for 12 compact starburst galaxies at z = 0.4–0.8. These massive galaxies ( ) are driving very fast outflows ( –3000 km s−1), and their light profiles are dominated by an extremely compact starburst component (half-light radius ∼ 100 pc). Our goal is to constrain the physical mechanisms responsible for launching these fast outflows by measuring the physical conditions within the central kiloparsec. Based on our stellar population analysis, the central component typically contributes ≈25% of the total stellar mass, and the central escape velocities km s−1 are a factor of two smaller than the observed outflow velocities. This Requires physical mechanisms that can accelerate gas to speeds significantly beyond the central escape velocities, and it makes clear that these fast outflows are capable of traveling into the circumgalactic medium, and potentially beyond. We find central stellar densities kpc−2 comparable to theoretical estimates of the Eddington limit, and we estimate surface densities within the central kiloparsec comparable to those of compact massive galaxies at . Relative to “red nuggets” and “blue nuggets” at , we find significantly smaller r e values at a given stellar mass, which we attribute to the dominance of a young stellar component in our sample and the better physical resolution for rest-frame optical observations at versus . We compare to theoretical scenarios involving major mergers and violent disk instability, and we speculate that our galaxies are progenitors of power-law ellipticals in the local universe with prominent stellar cusps.

Magellanic satellites in ΛCDM cosmological hydrodynamical simulations of the Local Group

ABSTRACT We use the APOSTLE ΛCDM cosmological hydrodynamical simulations of the Local Group to study the recent accretion of massive satellites into the halo of Milky Way (MW)-sized galaxies. These systems are selected to be close analogues to the Large Magellanic Cloud (LMC), the most massive satellite of the MW. The simulations allow us to address, in a cosmological context, the impact of the Clouds on the MW, including the contribution of Magellanic satellites to the MW satellite population, and the constraints placed on the Galactic potential by the motion of the LMC. We show that LMC-like satellites are twice more common around Local Group-like primaries than around isolated haloes of similar mass; these satellites come from large turnaround radii and are on highly eccentric orbits whose velocities at first pericentre are comparable with the primary’s escape velocity. This implies $V_{\rm esc}^{\rm MW} (50$ kpc) ∼ 365 km s−1, a strong constraint on Galactic potential models. LMC analogues contribute about two satellites with $M_*\gt 10^5\, \mathrm{ M}_\odot$, having thus only a mild impact on the luminous satellite population of their hosts. At first pericentre, LMC-associated satellites are close to the LMC in position and velocity, and are distributed along the LMC’s orbital plane. Their orbital angular momenta roughly align with the LMC’s, but, interestingly, they may appear to ‘counter-rotate’ the MW in some cases. These criteria refine earlier estimates of the LMC association of MW satellites: only the SMC, Hydrus1, Car3, Hor1, Tuc4, Ret2, and Phoenix2 are compatible with all criteria. Carina, Grus2, Hor2, and Fornax are less probable associates given their large LMC relative velocity.

Analysis of Forces generated in Human Body segments for Real time Space flight

Human body modelling for a space travel is a significant task to be considered for analyzing the forces generated on the human body segments. During the flight from earths atmosphere due to high escape velocity and acceleration, huge reaction forces will be generated on body segments which are beyond human capacitance. Recent studies evaluated the forces generated in various body segments by equipping external sensor vest or strips around the body parts where the application is limited for several on ground operations like hopping, sitting etc. and few studies analyzed the theoretical forces by modelling the human body as a second order spring mass damper system. The main objective of this work is to analyze the forces experienced by the human body segments for like Head, Neck, Upper Torso, Central Torso and Lower Torso for real time space flight data. The analysis is done on the anthropometric data of 50th percentile male US citizens available in literature by considering the human body as a second order spring mass damper system and the real time space flight parameters are taken from STS-121 space shuttle launched from Kennedy Space centre on July 4th 2006. The obtained resultant forces are plotted against the time of flight and it is observed that high forces are generated on Central Torso compared to remaining body parts and are varying with altitude of the vehicle.

Relativistic tidal accelerations in the exterior Schwarzschild spacetime

We study further a general-relativistic mechanism for the acquisition of tidal energy by free test particles near a gravitationally collapsed configuration. Specifically, we investigate the solutions of the timelike geodesic equation in a Fermi normal coordinate system established about the world line of an accelerated observer that remains spatially at rest in the exterior Schwarzschild spacetime. Such static observers in effect define the rest frame of the collapsed source. The gain in tidal energy is due to local spacetime curvature. Previous work in this direction in connection with astrophysical jets involved geodesic motion along the Kerr rotation axis where outward-moving particles could be tidally accelerated to almost the speed of light if their initial speed, as measured by the reference observer, is above a certain threshold escape velocity. We focus here for simplicity on the exterior Schwarzschild spacetime and show that the effective tidal acceleration to near the speed of light can occur for geodesic motion in certain radially outward directions. The implications of these results for the physics of gravitationally collapsed systems are briefly discussed.

Statistics of collision parameters computed from 2D simulations

ABSTRACTThere are two popular ways to speed up simulations of planet formation via increasing the collision probability: (i) confine motion to 2D, (ii) artificially enhance the physical radii of the bodies by an expansion factor. In this paper, I have performed 100 simulations each containing 104 interacting bodies and computed the collision parameters from the results of the runs. Each run was executed for a lower and a higher accuracy parameter. The main goal is to determine the probability distribution functions of the collision parameters and their dependence on the expansion factor. A simple method is devised to improve the determination of the collision parameters from the simulation data. It was shown that the distribution of the impact parameter is uniform and independent of the expansion factor. For real collisions, the impact velocity is greater than 1 mutual escape velocity, a finding that can be explained using the two-body problem. The results cast some doubts on simulations of the terrestrial planets’ final accretion that have assumed merge. Collision outcome maps were created adopting the fragmentation model of recent studies to estimate the number of different types of collisions. A detailed comparison with earlier works indicates that there are similarities as well as significant differences between the different works. The results indicate that as the planetary disc matures and the masses of the bodies differ progressively than the majority of collisions lead to mass growth either via partial accretion or via graze-and-merge collision.

Adrenergic Tone as an Intermediary in the Temperament Syndrome Associated With Flight Speed in Beef Cattle

The temperament of farm animals can influence their resilience to everyday variations within the managed production environment and has been under strong direct and indirect selection during the course of domestication. A prominent objective measure used for assessing temperament in beef cattle is the behavioral flight response to release from confinement in a crush or chute. This behavioral measure, termed flight speed (also known as escape velocity) is associated with physiological processes including body temperature, feeding behavior, growth rate, carcass composition, immune function, and health outcomes. This review examines the functional links between this suite of traits and adrenergic activity of the sympathetic nervous system and the adrenomedullary hormonal system. It is suggested that flight speed is the behavioral aspect of an underlying “flightiness” temperament syndrome, and that elevated adrenergic tone in animals with a high level of flightiness (i.e., flighty animals) tunes physiological activities toward a sustained “fight or flight” defense profile that reduces productivity and the capacity to flourish within the production environment. Nonetheless, despite a common influence of adrenergic tone on this suite of traits, variation in each trait is also influenced by other regulatory pathways and by the capacity of tissues to respond to a range of modulators in addition to adrenergic stimuli. It is suggested that tuning by adrenergic tone is an example of homeorhetic regulation that can help account for the persistent expression of behavioral and somatic traits associated with the flight speed temperament syndrome across the life of the animal. At a population level, temperament may modulate ecological fit within and across generations in the face of environmental variability and change. Associations of flight speed with the psychological affective state of the animal, and implications for welfare are also considered. The review will help advance understanding of the developmental biology and physiological regulation of temperament syndromes.

Departure of the thermal escape rate from the jeans escape rate for atomic hydrogen at Earth, Mars, and Pluto

The recent observations of the Pluto’s upper atmosphere by the UV spectrometer Alice on the New Horizons spacecraft mission have shown that it is not in slow hydrodynamic escape as predicted by some fluid models but not by kinetic models. This instrument also detects the Lyman-alpha emission of atomic hydrogen. On Pluto, the hydrogen atoms are produced by the photodissociation of methane and reside in an extended corona around Pluto. Similar to the case at Earth and Mars, the Jeans escape should be the dominant escape process for hydrogen on Pluto due to the low value of the escape parameter at the exobase. However, because of this escape, the velocity distribution at the exobase is truncated at high velocities and the Jeans’s escape rate needs to be reduced by a factor B. The goal of this study is to calculate the value of B for the hydrogen on Pluto and check if a plane parallel model, valid to estimate B on Earth and Mars is also valid to calculate B on Pluto.We compute B with a plane parallel model for the planets’ exospheres, and with a more realistic spherical model to check the validity of the plane parallel model. We find very good agreement between the two models for the current exobase temperatures at Earth, Mars and Pluto. The departure of the thermal hydrogen escape rate from the predicted Jeans escape rate is larger for Mars and Earth than Pluto, even though the escape parameter is lower on Pluto than Mars and Earth. This difference is due to the presence of a minimum in this correction factor for an escape parameter near 3. This minimum is due to the large fraction of particles with a velocity larger than the escape velocity at low escape parameter, leading to an upward-directed velocity distribution close to the Maxwellian distribution at the exobase. The factor B can be decomposed as the product of two terms: one associated with the departure of the distribution velocity from a Maxwellian distribution at the exobase, and the second, associated with the few collisions above the exobase, reducing the escape rate. The first term has a minimum as a function of exobase temperature, while the second term is a monotonically decreasing function of exobase temperature to an asymptotic value.

The antesonic condition for the explosion of core-collapse supernovae – II. Rotation and turbulence

ABSTRACT In the problem of steady free fall on to a standing shockwave around a central mass, the ‘antesonic’ condition limits the regime of stable accretion to $c_T^2/v_\mathrm{esc}^2\le 3/16$, where cT is the isothermal sound speed in the subsonic post-shock flow, and vesc is the escape velocity at the shock radius. Above this limit, it is impossible to satisfy both the Euler equation and the shock jump conditions, and the system transitions to a wind. This physics explains the existence of a critical neutrino luminosity in steady-state models of accretion in the context of core-collapse supernovae. Here, we extend the antesonic condition to flows with rotation and turbulence using a simple one-dimensional formalism. Both effects decrease the critical post-shock sound speed required for explosion. While quite rapid rotation is required for a significant change to the critical condition, we show that the level of turbulence typically achieved in supernova simulations can greatly impact the critical value of $c_T^2/v_\mathrm{esc}^2$. A core angular velocity corresponding to a millisecond rotation period after contraction of the proto-neutron star results in only a ∼5 per cent reduction of the critical curve. In contrast, near-sonic turbulence with specific turbulent kinetic energy $K/c_T^2=0.5-1$, leads to a decrease in the critical value of $c_T^2/v_{\rm esc}^2$ by ∼20 to 40 per cent. This analysis provides a framework for understanding the role of post-shock turbulence in instigating explosions in models that would otherwise fail and helps explain why multidimensional simulations explode more easily than their one-dimensional counterparts.

Micro analysis of riverbank sediment stability under different wetted surface conditions

Quantity of water entrapped between sediment particles imparts strength up to a limit and increases the stability of a riverbank. In the present study, this strength of the sediments has been investigated in terms of escape velocity of the sediments. Escape velocity has a considerable impact on the stability of the bank surface. Here, the “Truncated Pyramid Model (TPM)” for arrangement of the sediments has been utilized to determine escape velocity for different wetted surface conditions and inter-granular spaces. It has been found from the present investigation that irrespective of the variability in the riverbank morphology, the escape velocity attains a large value due to enhancement of the wetted surface area resulting in riverbank stability.

Blue extreme disk-runaway stars with Gaia EDR3

Since the discovery of hypervelocity stars in 2005, it has been widely believed that only the disruption of a binary system by a supermassive black hole at the Galactic center (GC), that is, the so-called Hills mechanism, is capable of accelerating stars to beyond the Galactic escape velocity. In the meantime, however, driven by the Gaia space mission, there is mounting evidence that many of the most extreme high-velocity early-type stars at high Galactic latitudes do originate in the Galactic disk and not in the GC. Moreover, the ejection velocities of these extreme disk-runaway stars exceed the predicted limits of the classical scenarios for the production of runaway stars. Based on proper motions from the Gaia early data release 3 and on recent and new spectrophotometric distances, we studied the kinematics of 30 such extreme disk-runaway stars, allowing us to deduce their spatial origins in and their ejection velocities from the Galactic disk with unprecedented precision. Only three stars in the sample have past trajectories that are consistent with an origin in the GC, most notably S5-HVS 1, which is the most extreme object in the sample by far. All other program stars are shown to be disk runaways with ejection velocities that sharply contrast at least with classical ejection scenarios. They include HVS 5 and HVS 6, which are both gravitationally unbound to the Milky Way. While most stars originate from within a galactocentric radius of 15 kpc, which corresponds to the observed extent of the spiral arms, a group of five stars stems from radii of about 21−29 kpc. This indicates a possible link to outer Galactic rings and a potential origin from infalling satellite galaxies.

The wide upper main sequence and main-sequence turnoff of the ∼ 800 Myr old star cluster NGC 1831

ABSTRACT We present the analysis of the colour–magnitude diagram (CMD) morphology of the ∼800 Myr old star cluster NGC 1831 in the Large Magellanic Cloud, exploiting deep, high-resolution photometry obtained using the Wide Field Camera 3 onboard the Hubble Space Telescope. We perform a simultaneous analysis of the wide upper main sequence and main-sequence turn-off observed in the cluster, to verify whether these features are due to an extended star formation or a range of stellar rotation rates, or a combination of these two effects. Comparing the observed CMD with Monte Carlo simulations of synthetic stellar populations, we derive that the morphology of NGC 1831 can be fully explained in the context of the rotation velocity scenario, under the assumption of a bimodal distribution for the rotating stars, with ∼40 per cent of stars being slow rotators (Ω/Ωcrit < 0.5) and the remaining ∼60 per cent being fast rotators (Ω/Ωcrit > 0.9). We derive the dynamical properties of the cluster, calculating the present cluster mass and escape velocity, and predicting their past evolution starting at an age of 10 Myr. We find that NGC 1831 has an escape velocity vesc = 18.4 km s−1 at an age of 10 Myr, above the previously suggested threshold of 15 km s−1 below which the cluster cannot retain the material needed to create second-generation stars. These results, combined with those obtained from the CMD morphology analysis, indicate that for the clusters whose morphology cannot be easily explained only in the context of the rotation velocity scenario, the threshold limit should be at least ∼20 km s−1.

A Common Origin for Low-mass Ratio Events Observed by LIGO and Virgo in the First Half of the Third Observing Run

Abstract In its third observing run, the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration has announced a potential neutron star−black hole (NS−BH) merger candidate, GW190426_152155. Together with GW190814, these two events belong to a class of binaries with a secondary mass less than 3 M ⊙. While the secondary system in GW190426_152155 is consistent with being a neutron star (NS) with a mass of , that of GW190814 is a object and counts as the first confirmed detection of a mass-gap object. Here we argue that these two events could have a common origin as follows: both are formed as NS−BH systems; however, the larger escape velocity of a system with more massive primary black hole (BH) increases the bound fraction of the ejecta material from the supernova explosion leading to the formation of a NS. This bound material forms a disk, which is preferentially accreted onto the NS. This scenario predicts the secondary component mass should correlate with the primary component mass, which is consistent with GW190426_152155 and GW190814. If this hypothesis is corroborated by upcoming observations, GW190814-like events can be excluded from the binary BH population when inferring their global characteristics.

The impact of urban block typology on pollutant dispersion

Block typology is a central component for urban planning and a key element to represent the urban form, which affects the airflow. Therefore, the aim of this work consists of investigating the impact of different urban block typologies in urban pollutant dispersion. Five typologies derived from real cities were investigated using the computational fluid dynamics technique: single-block, detached buildings, central courtyard, inner courtyards, and row. The numerical simulations were performed using URANS (Unsteady Reynolds-Averaged Navier-Stokes) equations and the κ−ω SST model to represent the turbulence effects. The model was validated using wind tunnel experimental data. Urban air quality was assessed using five parameters: mean age of air, net escape velocity, pollutant concentration at pedestrian level, and pollutant mass fluxes towards the urban canopy and outwards from it. The results showed that the single-block typology revealed an average pollutant concentration at pedestrian height 80% lower than that estimated in the detached building typology, which presented the highest concentration, probably due to the highest aspect ratio associated with permeable facades. Further, the higher the wind velocity, the lower the mean age of air. Finally, the unbuilt areas’ disposition within the block proved to be the more important parameter influencing the pollutant dispersion.

Dynamic behavior of chloride ion-electrically charged open carbon nanocone oscillators: A molecular dynamics study

This paper is intended to study the dynamic oscillatory behavior of chloride ion inside electrically charged open carbon nanocones (CNCs) using the molecular dynamics (MD) simulations. The small and wide ends of nanocone are assumed to be identically and uniformly charged with positive electric charges. In the simulation, the Tersoff-Brenner (TB) and the Lennard-Jones (LJ) potential functions are employed to evaluate the interatomic interactions between carbon atoms and the van der Waals (vdW) interactions between the ion and the nanocone, respectively. The Coulomb potential is also adopted to evaluate the electrostatic interactions between the ion and the electric charges distributed at both ends of nanocone. Numerical results are presented to examine the effects of magnitude of electric charges, initial separation distance and initial velocity on the mechanical oscillatory behavior of system and the obtained results are also compared with the ones related to an uncharged nanocone. It is found that operating frequency as well as escape velocity enhance considerably as a result of electrostatic interactions. It is further found that regardless of the value of electric charges, optimal oscillation frequency is achievable when no initial velocity is imposed on the ion initially located inside of nanocone with an offset of 2 Å from its small end.

Near‐horizon structure of escape zones of electrically charged particles around weakly magnetized rotating black hole: Case of oblique magnetosphere

AbstractWe study the effects of large‐scale magnetic fields on the dynamics of charged particles near a rotating black hole. We consider a scenario in which the initially neutral particles on geodesic orbits in the equatorial plane become ionized, and hence they are destabilized by the charging process. Fraction of charged particles are then accelerated out of the equatorial plane and then follow jet‐like trajectories with relativistic velocities. We explore nonaxisymmetric systems in which the magnetic field is inclined with respect to the black hole spin. We study the system numerically in order to locate the zones of escaping trajectories and compute the terminal escape velocity. By breaking the axial symmetry, we notice increasing fraction of unbound orbits which allow for acceleration to ultrarelativistic velocities.

Uncertainty principle, minimal escape velocities, and observability inequalities for Schrödinger Equations

Uncertainty principle, minimal escape velocities, and observability inequalities for Schrödinger Equations

Vortices and waves in light dark matter

In a galactic halo like the Milky Way, bosonic dark matter particles lighter than about 100 eV have a de Broglie wavelength larger than the average inter-particle separation and are therefore well described as a set of classical waves. This applies to, for instance, the QCD axion as well as to lighter axion-like particles such as fuzzy dark matter. We show that the interference of waves inside a halo inevitably leads to vortices, locations where chance destructive interference takes the density to zero. The phase of the wavefunction has non-trivial winding around these points. This can be interpreted as a non-zero velocity circulation, so that vortices are sites where the fluid velocity has a non-vanishing curl. Using analytic arguments and numerical simulations, we study the properties of vortices and show they have a number of universal features: (1) In three spatial dimensions, the generic defects take the form of vortex rings. (2) On average there is about one vortex ring per de Broglie volume and (3) generically only single winding (± 1) vortices are found in a realistic halo. (4) The density near a vortex scales as r2 while the velocity goes as 1/r, where r is the distance to vortex. (5) A vortex segment moves at a velocity inversely proportional to its curvature scale so that smaller vortex rings move faster, allowing momentary motion exceeding escape velocity. We discuss observational/experimental signatures from vortices and, more broadly, wave interference. In the ultra-light regime, gravitational lensing by interference substructures leads to flux anomalies of 5–10 % in strongly lensed systems. For QCD axions, vortices lead to a diminished signal in some detection experiments but not in others. We advocate the measurement of correlation functions by axion detection experiments as a way to probe and capitalize on the expected interference substructures.

Particle dynamics around quintessential Reissner-Nordström black hole

In this article, we study the dynamics of neutral as well as charged particle in the presence of magnetic field around Reissner-Nordström black hole surrounded by quintessence by taking into account Noether symmetries and conservation laws in the corresponding spacetime. Using these conservation laws, we explore the effect of angular momentum, quintessence parameter, and magnetic field graphically on the dynamics of neutral/charged particles in the context of the effective potential, effective force, and escape velocity. Additionally, we investigate the orbit stability of the said spacetime with the help of the Lyapunov exponent.