Star Formation Research Papers - Academia.edu (original) (raw)

""Knowledge of the physical and chemical processes which occur within the circum-stellar nebula of a newly formed star is still uncertain and permits a number of distinct theories to account for the formation of planets. In order to gain a greater insight into the complexities of planetary formation, researchers have concentrated on 'realistic' simulations of clearly defined and limited aspects of the problem of the formation of the Solar System. Attempts to describe the nature of planetary systems of other stars have been left largely to popular speculation.
The microcomputer model presented here produces a wide range of data for possible planetary systems with primary stars in the mass range 0.6 - 1.3 M⊙. A synthesis of current theory, research and speculation, the purpose of this model is not to add to our understanding of the processes that form planets, but to give an integrated view of the possible nature of extra-solar planetary systems and to investigate the possibility of a systematic variation in planetary characteristics with primary mass. ""

- by Martyn Fogg
- •
- Star Formation, Extrasolar planets, Planet Formation, Habitable Exoplanets

Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medium (ISM) mass. The structure, properties and lifetimes of molecular clouds are determined by the overall dynamics and evolution of a very complex system – the ISM. Understanding the physics of the ISM is of prime importance not only for Galactic but also for extragalactic and cosmological studies. Most of the ISM volume (∼ 65%) is filled with diffuse gas at temperatures between 3000 and 300 000 K, representing about 50% of the ISM mass. The physics of accretion and outflow. Powerful outflows are known to regulate angular momentum transport during star formation, the so-called accretion–outflow engine. Elementary physical considerations show that, to be efficient, the acceleration region for the outflows must be located close to the star (within 1 AU) where the gravitational field is strong. According to recent numerical simulations, this is also the region where terrestrial planets could form after 1 Myr. One should keep in mind that today the only evidence for life in the Universe comes from a planet located in this inner disk region (at 1 AU) from its parent star. The temperature of the accretion–outflow engine is between 3000 and 10 7 K. After 1 Myr, during the classical T Tauri stage, extinction is small and the engine becomes naked and can be observed at ultraviolet wavelengths. The physics of planet formation. Observations of volatiles released by dust, planetesimals and comets provide an extremely powerful tool for determining the relative abundances of the vaporizing species and for studying the photochemical and physical processes acting in the inner parts of young planetary systems. This region is illuminated by the strong UV radiation field produced by the star and the accretion–outflow engine. Absorption spectroscopy provides the most sensitive tool for determining the properties of the circumstellar gas as well as the characteristics of the atmospheres of the inner planets transiting the stellar disk. UV radiation also pumps the electronic transitions of the most abundant molecules (H 2, CO, etc.) that are observed in the UV. Here we argue that access to the UV spectral range is essential for making progress in this field, since the resonance lines of the most abundant atoms and ions at temperatures between 3000 and 300 000 K, together with the electronic transitions of the most abundant molecules (H 2, CO, OH, CS, S 2, CO 2+, C 2, O 2, O3, etc.) are at UV wavelengths. A powerful UV-optical instrument would provide an efficient mean for measuring the abundance of ozone in the atmosphere of the thousands of transiting planets expected to be detected by the next space missions (GAIA, Corot, Kepler, etc.). Thus, a follow-up UV mission would be optimal for identifying Earth-like candidates.

- by Ana I Gomez de Castro
- •
- Interstellar Medium, Star Formation, Molecular Clouds, Complex System

Evidence for the existence of planetary mass objects, unattached to any star and free-floating in interstellar space, has recently emerged. In this paper, this evidence and the history of the concept of free-floating planets is reviewed and a classification is proposed, based on mode of origin. It is suggested that free floating planets can originate in two settings: 1) interstellar space, where the object forms in the manner of a star; 2) circumstellar space, where the object forms in the manner of a conventional planet and is subsequently lost to interstellar space. We designate the former type of object a planetar and the latter an unbound planet. Three possible scenarios of planetar formation and four scenarios of unbound planet origin are explored and discussed. Estimates of the abundance of these objects suggest that planetars in the mass range of 1 – 13 M♃ may be about as common as stars and brown dwarfs. The number of unbound planets however may exceed the number of stars by two orders of magnitude, although most of them should be low-mass rock/ice planetary embryos ejected from planetary systems in formation. It seems likely therefore that advances in observational techniques, such as infrared astronomy and microlensing, will lead to the discovery of many more free-floating planets in the future, securing their recognition as genuine astrophysical objects.

- by Martyn Fogg
- •
- Star Formation, Astrophysics, Extrasolar planets, Planet Formation

Many giant exoplanets are thought to have formed in the outer regions of a protoplanetary
disk, and to have then migrated close to the central star. Hence, it is uncertain
whether terrestrial planets can grow and be retained in these `hot-Jupiter' systems.
Previous speculations, based on the assumption that migrating giant planets will clear
planet-forming material from their swept zone, have concluded that such systems
should lack terrestrial planets.
This thesis presents a succession of four planet formation models, of increasing
sophistication, aimed at examining how an inner system of solid bodies, undergoing
terrestrial planet formation, evolves under the inuence of a giant planet undergoing
inward type II migration. Protoplanetary growth is handled by an N+N'-body code,
capable of simulating the accretion of a two-phase protoplanetplanetesimal population,
and tracking their volatiles content. Gas dynamics and related dissipative processes
are calculated with a linked viscous gas disk algorithm capable of simulating:
gas accretion onto the central star and photoevaporation; type II migration of the giant
planet; type I migration of protoplanets; and the effect of gas drag on planetesimals.
In all simulations, a large fraction of the inner system material survives the passage
of the giant, either by accreting into massive planets shepherded inward of the
giant (reminiscent of the short-period `hot-Earths' discovered recently), or by being
scattered into external orbits. Typically, sufcient mass is scattered outward to provide
for the eventual accretion of a set of terrestrial planets in external orbits.
The results of this thesis lead to the prediction that hot-Jupiter systems are likely
to harbor water-rich terrestrial planets in their habitable zones and hot-Earths may
also be present. These planets may be detected by future planet search missions.

- by Martyn Fogg
- •
- Planetary Science, Star Formation, Astrobiology, Exoplanets
- by Zulfikar Najmudin
- •
- Star Formation, Active Galactic Nuclei, Early Universe, Multidisciplinary

The presence of unseen mass in the solar neighbourhood has prompted modelling of, and searches for, a population of cool, low mass stars to make up the deficit. Such brown dwarfs are thought to exist within a mass range of 0.01 M⊙ < M < 0.08 M⊙. In this paper the possibility of the existence of interstellar planets (ISPs) of mass range 5x10^-9 M⊙ < M < 0.01 M⊙ is examined. Six potential modes of formation of ISPs are identified, although some are mutually exclusive, depending of different cosmogonic hypotheses. ISPs are of two basic types: those formed solitary within molecular clouds and those formed within, and subsequently unbound from, planetary systems. While the existence of the former is uncertain, interstellar planets of the unbound variety almost definitely exist, although not in sufficient quantity to account for the unseen mass. The number density of unbound planets in the solar neighbourhood may be of a similar, or greater, order of magnitude to that of stars, the majority of them being massive planetesimals ejected from planetary systems in formation. The nearest extra-solar planet may thus be closer to the solar system than the nearest star.

- by Martyn Fogg
- •
- Star Formation, Extrasolar planets, Planet Formation, Free Floating Planets.
- by Guillermo Gonzalez
- •
- Geochemistry, Geophysics, Interstellar Medium, Cosmochemistry

"A lengthy analysis of the output of the "Silicon Creation" model is presented.
Seven thousand five hundred microcomputer simulations of stars in the mass range 0.6 - 1.3M⊙ suggest that habitable planets are to be expect to occur around stars of between 0.8 - 1.2 M⊙ and most commonly around stars between 0.95 - 1.05 M⊙. The characteristics of these planets range between extremes of mass ~ 0.4 - 2.8 M_e; surface gravity ~ 0.7 - 1.5 g; atmospheric pressure ~ 500 - 2000 mb; average surface temperature ~ 1 C - 21 C; hydrosphere ~ 50 - 99%.
An extended simulation of an evolving volume of Galactic disc space, 270 ly in diameter, containing 100,000 star systems of maximum age 10^10 years was performed, assuming constant stellar birthrate and rising metallicity with time. 86 habitable planets were produced giving a value for the ratio of habitable planets to stars in the disc N_HP / N_*disc = 8.6x10^4. The average separation between habitable planets is therefore ~ 50 ly and the number of habitable planets in the Galaxy is approximately 90 million.
Comparison of these results is made with those of other authors and uncertainties inherent in the "Silicon Creation" model are briefly discussed."

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Extrasolar planets, Planet Formation

A Monte Carlo computer model of extra-solar planetary formation and evolution, which includes the planetary geochemical carbon cycle, is presented. The results of a run of one million galactic disc stars are shown where the aim was to assess the possible abundance of both biocompatible and habitable planets. (Biocompatible planets are defined as worlds where the long-term presence of surface liquid water provides environmental conditions suitable for the origin and evolution of life. Habitable planets are those worlds with more specifically Earth-like conditions.) The model gives an estimate of 1 biocompatible planet per 39 stars, with the subset of habitable planets being much rarer at 1 such planet per 413 stars. The nearest biocompatible planet may thus lie ~ 14 LY distant and the nearest habitable planet ~ 31 LY away. If planets form in multiple star systems then the above planet/star ratios may be more than doubled. By applying these results to stars in the solar neighbourhood, it is possible to identify 28 stars at distances of < 22 LY with a non-zero probability of possessing a biocompatible planet.

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Extrasolar planets, Planet Formation
- by Bruce Johnson and +2
- •
- Star Formation, Astronomy, Astronomy Education, Surveys
- by Francis Albarede
- •
- Pharmacology, Biochemistry, Bioinformatics, Evolutionary Biology

About a fifth of the exoplanetary systems that have been discovered contain a so-called hot-Jupiter – a giant planet orbiting within 0.1 AU of the central star. Since these stars are typically of the F/G spectral type, the orbits of any terrestrial planets in their habitable zones at y1 AU should be dynamically stable. However, because hot-Jupiters are thought to have formed in the outer regions of a protoplanetary disc, and to have then migrated through the terrestrial planet zone to their final location, it is uncertain whether terrestrial planets can actually grow and be retained in these systems. In this paper we review attempts to answer this question. Initial speculations, based on the assumption that migrating giant planets will clear planet-forming material from their swept zone, all concluded that hot-Jupiter systems should lack terrestrial planets. We show that this assumption may be incorrect, for when terrestrial planet formation and giant planet migration are simulated simultaneously, abundant solid material is predicted to remain from which terrestrial planet growth can resume.

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Exoplanets, Astrophysics

""Context. Extrasolar giant planets are found to orbit their host stars with a broad range of semi-major axes 0.02 ≤ a ≤ 6 AU. Current theories suggest that giant planets orbiting at distances between 0.02−2 AU probably formed at larger distances and migrated to their current locations via type II migration, disturbing any inner system of forming terrestrial planets along the way. Migration probably halts because of fortuitously-timed gas disk dispersal.
Aims. The aim of this paper is to examine the effect of giant planet migration on the formation of inner terrestrial planet systems. We consider situations in which the giant planet halts migration at semi-major axes in the range 0.13−1.7 AU due to gas disk dispersal, and examine the effect of including or neglecting type I migration forces on the forming terrestrial system.
Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating gas loss via accretion onto the central star and photoevaporation, gap formation by the giant planet, type II migration of the giant, optional type I migration of protoplanets, and gas drag on planetesimals.
Results. Most of the inner system planetary building blocks survive the passage of the giant planet, either by being shepherded inward or scattered into exterior orbits. Systems of one or more hot-Earths are predicted to form and remain interior to the giant planet, especially if type II migration has been limited, or where type I migration has affected protoplanetary dynamics. Habitable planets in low-eccentricity warm-Jupiter systems appear possible if the giant planet makes a limited incursion into the outer regions of the habitable zone (HZ), or traverses its entire width and ceases migrating at a radial distance of less than half that of the HZ’s inner edge.
Conclusions. Type II migration does not prevent terrestrial planet formation. A wide variety of planetary system architectures exists that can potentially host habitable planets.""

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Exoplanets, Astrophysics

We have analyzed Spitzer and NASA/IRTF 2 - 35 \mum spectra of the warm, ~350 K circumstellar dust around the nearby MS star {\eta} Corvi (F2V, 1.4 \pm 0.3 Gyr). The spectra show clear evidence for warm, water- and carbon-rich dust at ~3 AU from the central star, in the system's Terrestrial Habitability Zone. Spectral features due to ultra-primitive cometary material were found, in addition to features due to impact produced silica and high temperature carbonaceous phases. At least 9 x 10^18 kg of 0.1 - 100 \mum warm dust is present in a collisional equilibrium distribution with dn/da ~ a^-3.5, the equivalent of a 130 km radius KBO of 1.0 g/cm^3 density and similar to recent estimates of the mass delivered to the Earth at 0.6 - 0.8 Gyr during the Late Heavy Bombardment. We conclude that the parent body was a Kuiper-Belt body or bodies which captured a large amount of early primitive material in the first Myrs of the system's lifetime and preserved it in deep freeze at ~150 AU. At ~1.4 Gyr they were prompted by dynamical stirring of their parent Kuiper Belt into spiraling into the inner system, eventually colliding at 5-10 km/sec with a rocky planetary body of mass \leq MEarth at ~3 AU, delivering large amounts of water (>0.1% of MEarth's Oceans) and carbon-rich material. The Spitzer spectrum also closely matches spectra reported for the Ureilite meteorites of the Sudan Almahata Sitta fall in 2008, suggesting that one of the Ureilite parent bodies was a KBO.

- by Andreas Morlok
- •
- Infrared Astronomy, Planetary Science, Star Formation, Infrared Optics

"Context. There are numerous extrasolar giant planets which orbit close to their central stars. These “hot-Jupiters” probably formed in the outer, cooler regions of their protoplanetary disks, and migrated inward to ∼0.1 AU. Since these giant planets must have migrated through their inner systems at an early time, it is uncertain whether they could have formed or retained terrestrial planets.
Aims. We present a series of calculations aimed at examining how an inner system of planetesimals/protoplanets, undergoing terrestrial planet formation, evolves under the influence of a giant planet undergoing inward type II migration through the region bounded between 5–0.1 AU.
Methods. We have previously simulated the effect of gas giant planet migration on an inner system protoplanet/planetesimal disk using a N-body code which included gas drag and a prescribed migration rate. We update our calculations here with an improved model that incorporates a viscously evolving gas disk, annular gap and inner-cavity formation due to the gravitational field of the giant planet, and self-consistent evolution of the giant’s orbit.
Results. We find that 60% of the solids disk survives by being scattered by the giant planet into external orbits. Planetesimals are scattered outward almost as efficiently as protoplanets, resulting in the regeneration of a solids disk where dynamical friction is strong and terrestrial planet formation is able to resume. A simulation that was extended for a few Myr after the migration of the giant planet halted at 0.1 AU, resulted in an apparently stable planet of ∼2 m⊕ forming in the habitable zone. Migration–induced mixing of volatile-rich material from beyond the “snowline” into the inner disk regions means that terrestrial planets that form there are likely to be water-rich.
Conclusions. We predict that hot-Jupiter systems are likely to harbor water-abundant terrestrial planets in their habitable zones. These planets may be detected by future planet search missions."

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Exoplanets, Astrophysics

Giant planets found orbiting close to their central stars, the so called “hot Jupiters”, are thought to have originally formed in the cooler outer regions of a protoplanetary disk and then to have migrated inward via tidal interactions with the nebula gas. We present the results of N-body simulations which examine the effect such gas giant planet migration has on the formation of terrestrial planets. The models incorporate a 0.5 Jupiter mass planet undergoing type II migration through an inner protoplanet-planetesimal disk, with gas drag included. Each model is initiated with the inner disk being at successively increased levels of maturity, so that it is undergoing either oligarchic or giant impact style growth as the gas giant migrates. In all cases, a large fraction of the disk mass survives the passage of the giant, either by accreting into massive terrestrial planets shepherded inward of the giant, or by being scattered into external orbits. Shepherding is favored in younger disks where there is strong dynamical friction from planetesimals and gas drag is more influential, whereas scattering dominates in more mature disks where dissipation is weaker. In each scenario, sufficient mass is scattered outward to provide for the eventual accretion of a set of terrestrial planets in external orbits, including within the system’s habitable zone. This scattering, however, significantly reduces the density of solid material, indicating that further accretion will occur over very long time scales. A particularly interesting result is the generation of massive, short period, terrestrial planets from compacted material pushed ahead of the giant. These planets are reminiscent of the short period Neptune-mass planets discovered recently, suggesting that such “hot Neptunes” could form locally as a by product of giant planet migration.

- by Martyn Fogg
- •
- Star Formation, Exoplanets, Astrophysics, Nbody simulations
- by Stuart Mangles
- •
- Star Formation, Active Galactic Nuclei, Early Universe, Multidisciplinary

"Context. Our previous models of a giant planet migrating through an inner protoplanet/planetesimal disk find that the giant shepherds a portion of the material it encounters into interior orbits, whilst scattering the rest into external orbits. Scattering tends to dominate, leaving behind abundant material that can accrete into terrestrial planets.
Aims. We add to the possible realism of our model by simulating type I migration forces which cause an inward drift, and strong eccentricity and inclination damping of protoplanetary bodies. This extra dissipation might be expected to enhance shepherding at the expense of scattering, possibly modifying our previous conclusions.
Methods. We employ an N-body code that is linked to a viscous gas disk algorithm capable of simulating: gas accretion onto the
central star; gap formation in the vicinity of the giant planet; type II migration of the giant planet; type I migration of protoplanets; and the effect of gas drag on planetesimals. We use the code to re-run three scenarios from a previous work where type I migration
was not included.
Results. The additional dissipation introduced by type I migration enhances the inward shepherding of material but does not severely reduce scattering. We find that >50% of the solids disk material still survives the migration in scattered exterior orbits: most of it well placed to complete terrestrial planet formation at <3 AU. The shepherded portion of the disk accretes into hot-Earths, which survive in interior orbits for the duration of our simulations.
Conclusions. Water-rich terrestrial planets can form in the habitable zones of hot-Jupiter systems and hot-Earths and hot-Neptunes may also be present. These systems should be targets of future planet search missions."

- by Martyn Fogg
- •
- Star Formation, Astrobiology, Exoplanets, Astrophysics
- by Bernard Heymann
- •
- Algorithms, Image Processing, Electron Microscopy, Structural Biology

Supermassive black holes have generally been recognized as the most destructive force in nature. But in recent years, they have undergone a dramatic shift in paradigm. These objects may have been critical to the formation of structure in the early universe, spawning bursts of star formation and nucleating proto-galactic condensations. Possibly half of all the radiation produced after the Big

- by Fulvio Melia
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- Star Formation, Early Universe, Big Bang, Black Hole

Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connec- tions. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed ”reconnec- tion diffusion”. The astrophysical implications of this con- cept include heat transfer in plasmas, advection of heavy el- ements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that mag- netic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection dif- fusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the pro- cess that is termed ”ambipolar diffusion”. The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, am- bipolar diffusion predicts that the coupling of mass and mag- netic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view, i.e. appealing to the reconnection of flux tubes and to the dif-
the dynamics of many key processes, including magnetic re- connection. Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connec- tions. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed ”reconnec- tion diffusion”. The astrophysical implications of this con- cept include heat transfer in plasmas, advection of heavy el- ements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that mag- netic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection dif- fusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the pro- cess that is termed ”ambipolar diffusion”. The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, am- bipolar diffusion predicts that the coupling of mass and mag- netic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view. We make use of the Lazarian & Vishniac 1999 theory of magnetic reconnection and show that this theory is applicable to the partially ionized gas. We quantify the reconnection diffusion rate both for weak and strong MHD turbulence and address the problem of recon- nection diffusion acting together with ambipolar diffusion. In addition, we provide a criterion for correctly representing the magnetic diffusivity in simulations of star formation. We discuss the intimate relation between the processes of recon- nection diffusion, field wandering and turbulent mixing of a magnetized media and show that the role of the plasma ef- fects is limited to ”breaking up lines” on small scales and does not affect the rate of reconnection diffusion. We ad- dress the existing observational results and demonstrate how reconnection diffusion can explain the puzzles presented by observations, in particular, the observed higher magnetiza- tion of cloud cores in comparison with the magnetization of envelopes. We also outline a possible set of observational tests of the reconnection diffusion concept and discuss how the application of the new concept changes our understand- ing of star formation and its numerical modeling. Finally, we outline the differences of the process of reconnection diffusion and the process of accumulation of matter along magnetic field lines that is frequently invoked to explain the results of numerical simulations

- by A. Lazarian
- •
- Turbulence, Star Formation, Cosmic Rays, Magnetic Reconnection
- by Peter Höflich and +2
- •
- Stellar Evolution, Interstellar Medium, Star Formation, Big Bang
- by Vincent Minier
- •
- Gravitation, Star Formation, Dark Matter, Theory
- by Alessandra Aloisi
- •
- Star Formation

Low mass stars, like our Sun, are born from the collapse of a molecular cloud. The matter falls in the center of the cloud, creating a protoplanetary disk surrounding a protostar. Planets and other solar system bodies will be formed in the disk.The chemical composition of the interstellar matter and its evolution during the formation of the disk are important to better understand the formation process of these objects.I studied the chemical and physical evolution of this matter, from the cloud to the disk, using the chemical gas-grain code Nautilus.A sensitivity study to some parameters of the code (such as elemental abundances and parameters of grain surface chemistry) has been done. More particularly, the updates of rate coefficients and branching ratios of the reactions of our chemical network showed their importance, such as on the abundances of some chemical species, and on the code sensitivity to others parameters.Several physical models of collapsing dense core have also been considered. The more complex and solid approach has been to interface our chemical code with the radiation-magneto-hydrodynamic model of stellar formation RAMSES, in order to model in three dimensions the physical and chemical evolution of a young disk formation. Our study showed that the disk keeps imprints of the past history of the matter, and so its chemical composition is sensitive to the initial conditions.

- by Ugo Hincelin
- •
- Interstellar Medium, Magnetohydrodynamics, Star Formation, Astrochemistry

How mass is accumulated from cloud-scale down to individual stars is a key open question in understanding high-mass star formation. Here, we present the mass accumulation process in a hub-filament cloud G22 that is composed of four supercritical filaments. Velocity gradients detected along three filaments indicate that they are collapsing with a total mass infall rate of about 440 M e Myr −1 , suggesting the hub mass would be doubled in six free-fall times, adding up to ∼2 Myr. A fraction of the masses in the central clumps C1 and C2 can be accounted for through large-scale filamentary collapse. Ubiquitous blue profiles in HCO + (3–2) and 13 CO(3–2) spectra suggest a clump-scale collapse scenario in the most massive and densest clump C1. The estimated infall velocity and mass infall rate are 0.31 km s −1 and 7.2×10 −4 M e yr −1 , respectively. In clump C1, a hot molecular core (SMA1) is revealed by the Submillimeter Array observations and an outflow-driving high-mass protostar is located at the center of SMA1. The mass of the protostar is estimated to be 11–15 M e and it is still growing with an accretion rate of 7×10 −5 M e yr −1. The coexistent infall in filaments, clump C1, and the central hot core in G22 suggests that pre-assembled mass reservoirs (i.e., high-mass starless cores) may not be required to form high-mass stars. In the course of high-mass star formation, the central protostar, the core, and the clump can simultaneously grow in mass via core-fed/disk accretion, clump-fed accretion, and filamentary/cloud collapse.

- by Frank Shu
- •
- Organic Chemistry, Interstellar Medium, Magnetohydrodynamics, Astrophysical Plasma
- by Melvyn Wright
- •
- Organic Chemistry, Astrophysical Plasma, Star Formation, High Resolution

HST is very well tailored for observations of extragalactic star clusters. One obvious reason is HST's high spatial resolution, but equally important is the wavelength range offered by the instruments on board HST, in particular the blue and near-UV coverage which is essential for age-dating young clusters. HST observations have helped establish the ubiquity of young massive clusters (YMCs) in a wide variety of star-forming environments, from dwarf galaxies and spiral disks to nuclear starbursts and mergers. These YMCs have masses and sizes similar to those of old globular clusters (GCs), and the two may be closely related. A large fraction of all stars seem to be born in clusters, but most clusters disrupt rapidly and the stars disperse to become part of the field population. In most cases studied to date the luminosity functions of young cluster systems are well fit by power-laws dN(L)/dL ~ L^-2, and the luminosity of the brightest cluster can (with few exceptions) be predicted from simple sampling statistics. Mass functions have only been constrained in a few cases, but appear to be well approximated by similar power-laws. The absence of any characteristic mass scale for cluster formation suggests that star clusters of all masses form by the same basic process, without any need to invoke special mechanisms for the formation of YMCs. It is possible, however, that special conditions can lead to the formation of a few YMCs in some dwarfs where the mass function is discontinuous. Further studies of mass functions for star clusters of different ages may help test the theoretical prediction that the power-law mass distribution observed in young cluster systems can evolve towards the approximately log-normal distribution seen in old GC systems.

- by mary sushma
- •
- Star Formation, Case Study, Dwarf Galaxies, Power Law
- by Ángeles Díaz
- •
- Stellar Evolution, Star Formation, High Density Concrete, Ionizing Radiation
- by James Binney and +3
- •
- Star Formation, Active Galactic Nuclei, Galaxy Formation and Evolution, Multidisciplinary
- by Prince Sky
- •
- Star Formation, Data Collection, Spectrum

It is conjectured that phenomena in biological microworld could be equated with astrophysical principles of gravitation. Fluids, gases that constitute 50-90 % of the total accredited biomass causes seclusion from stronger external gravitational fields. Seclusion due to buoyant condition is reflected in apparent ‘weight’ reduced. The g-value (self) to the tune of nanometer per second square in a massive body of a planet may be negligible, but in an isolated living mass at picometer distance, such acceleration is quite a significant force. Homogeneous and heterogeneous accretion; heating and cooling phenomena as well as the rhythmic pattern of growth due to elastic collisions in massive star; heat transfer mechanisms viz. radiation, (perspiration), conduction and convection; site of human core body temperature at liver, kidney, heart and parts of brain at central region under initial circular fetus situation; or coldest part of the periphery at toe, foot, hand demonstrates similarity between biological and astrophysical words. Mechanical movement of macromolecules under neutral buoyant condition of the principle ‘heavier molar mass plus higher the density- faster the central travel from periphery’ for nucleic acid and protein; fats & lipids in addition to molar mass and density- variation in temperature; distribution carbohydrates in protoplasm under miscible condition due to solubility under granular soil and gel properties were equated with movement phenomena under astrophysical principle. Centrifugation as standard protocol for separating organelles is considered as inversion or reversing the natural setting on losing its compression memory.

- by Iresh Ranjan Bhattacharjee
- •
- Gravitation, Quantum Gravity, Molecular Biology, Star Formation
- by Lennart Lindegren
- •
- Star Formation, Dark Matter, Dust (Astronomy & Astrophysics), Data Reduction

In order to explore the properties of extreme outer stellar disks, we obtained ultra-deep V and GALEX ultraviolet (UV) images of four dwarf irregular galaxies and one blue compact dwarf galaxy, and ultra-deep B images of three of these. Our V-band surface photometry extends to 29.5 mag arcsec-2. We convert the FUV and V-band photometry, along with Hα photometry obtained in a larger survey, into radial star formation rate profiles that are sensitive to timescales from 10 Myr to the lifetime of the galaxy. We also obtained H I-line emission data and compare the stellar distributions, surface brightness profiles, and star formation rate profiles to H I-line emission maps, gas surface density profiles, and gas kinematics. Our data lead us to two general observations. First, the exponential disks in these irregular galaxies are extraordinarily regular. We observe that the stellar disks continue to decline exponentially as far as our measurements extend. In spite of lumpiness in the distribution of young stars and H I distributions and kinematics that have significant unordered motions, sporadic processes that have built the disks—star formation, radial movement of stars, and perhaps even perturbations from the outside—have, nevertheless, conspired to produce standard disk profiles. Second, there is a remarkable continuity of star formation throughout these disks over time. In four out of five of our galaxies the star formation rate in the outer disk measured from the FUV tracks that determined from the V-band, to within factors of five, requiring star formation at a fairly steady rate over the galaxy's lifetime. Yet, the H I surface density profiles generally decline with radius more shallowly than the stellar light, and the gas is marginally gravitationally stable against collapse into clouds. Outer stellar disks are challenging our concepts of star formation and disk growth and provide a critical environment in which to understand processes that mold galaxy disks.

- by Tyler Nordgren
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- Star Formation, Ultraviolet, Astronomical

Models of terrestrial planet formation in the presence of a migrating giant planet have challenged the notion that hot-Jupiter systems lack terrestrial planets. We briefly review this issue and suggest that hot-Jupiter systems should be prime targets for future observational missions designed to detect Earth-sized and potentially habitable worlds.

- by Martyn Fogg
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- Star Formation, Exoplanets, Extrasolar planets, Planet Formation

The study of satellite galaxies can provide information on the merging and aggregation processes which, according to the hierarchical clustering models, form the larger spiral galaxies we observe. With the aim of testing hierarchical models of galaxy formation, we have conducted an observational program which comprises H$\alpha$ imaging for both the parent and the satellite galaxies, taken from the compilation by Zaritsky et al. (1997) that contains 115 galaxies orbiting 69 primary isolated spiral galaxies. We have observed a subsample of 37 spiral and irregular galaxies taken from the compilation mentioned above. The aim of this study is to determine star formation properties of the sample galaxies. In this work we present the preliminary results of this program that we have carried out with the 1.8-m Vatican Telescope (VATT).

- by Kimberly Ennico
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- Genetics, Interstellar Medium, Star Formation, HII Regions
- by Mark Krumholz
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Infrared

We present deep, high velocity resolution ( ~ 1.6 km s-1) Giant Meterwave Radio Telescope HI 21 cm synthesis images for the faint (MB ~ -12.1) dwarf irregular galaxy GR8. We find that the velocity field of the galaxy shows a clear... more

- by Ayesha Begum
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- Star Formation, Dust (Astronomy & Astrophysics), HII Regions, Galaxy evolution

In this paper, we present the spectral energy distributions (SEDs) modeling of ten massive young stellar objects (MYSOs) and subsequently estimated different physical and structural/geometrical parameters for each of the ten central YSO outflow candidates along with their associated circumstellar disks and infalling envelopes. The SEDs for each of the MYSOs been reconstructed by using 2MASS,
MSX, IRAS, IRAC & MIPS, SCUBA, WISE, SPIRE and IRAM data, with the help of a SED Fitting Tool that uses a grid of 2D radiative transfer models. Using the detailed analysis of SEDs and subsequent estimation of physical and geometrical parameters for the central YSO sources along with its
circumstellar disks and envelopes, the cumulative distribution of the stellar, disk and envelope parameters
can be analysed. This leads to a better understanding of massive star formation processes in their respective star forming regions in different molecular clouds.

- by Dr. Kamal Kumar Tanti
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- Star Formation, Young stellar objects

Dwarf irregular galaxies are unique laboratories for studying the interaction between stars and the interstellar medium in low mass environments. We present the highest spatial resolution observations to date of the neutral hydrogen content of the Local Group dwarf irregular galaxy WLM. We find that WLM's neutral hydrogen distribution is typical for a galaxy of its type and size and derive an HI mass of 6.3e7 Msun for WLM. In addition, we derive an HI extent for WLM of 30 arcmin, which is much less than the 45 arcmin extent found by Huchtmeier, Seiradakis, and Materne (1981). We show that the broken ring of high column density neutral hydrogen surrounding the center of WLM is likely the result of star formation propagating out from the center of the galaxy. The young stars and Ha emission in this galaxy are mostly correlated with the high column density neutral hydrogen. The gap in the central ring is the result of star formation in that region using up, blowing out, or ionizing all of the neutral hydrogen. Like many late-type galaxies, WLM's velocity field is asymmetric with the approaching (northern) side appearing to be warped and a steeper velocity gradient for the approaching side than for the receding side in the inner region of the galaxy. We derive a dynamical mass for WLM of 2.16e9 Msun.

- by Tyler Nordgren
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- Interstellar Medium, Star Formation, High Resolution, Spatial resolution

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar.

- by Sukyoung Kim
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- Organic Chemistry, Astrophysical Plasma, Star Formation, Old Age

The problems with the notion of black holes are numerous, but I'll go through a few of the main ones. Black Holes as the core of spiral galaxies: When we look at pictures of spiral galaxies, intuitively we're reminded of whirlpools or the gaseous equivalents, such as tornadoes or dust devils. That intuition leads us to see the 'arms' of the spiral as 'trailing', which implies that the galaxy, in the same sense as a whirlpool, is 'pulling' matter in to it. The solar system is posited as being, currently, towards the end of one such 'trailing' arm. The problem with this intuition is that whirlpools and equivalents can only form where the 'forces' of things surrounding them are greater than the forces generated by the whirlpool itself. In the case of a galaxy, where there is very little between it and the next galaxy, that's problematic. Granted there is such a thing as 'dark matter' and 'dark energy', it would have to be fairly evenly distributed both within and without the galaxy, otherwise it would be detectable and not 'dark', that distribution means that it can't change the overall sense that there's very little between galaxies, it just adds the qualifier 'very little that has any effective capacity " between galaxies. Observationally, this difference and therefore the intuition that ignores it, are incorrect. The spin of spiral galaxies, insofar as it can be determined (spiral galaxies spin at very different rates, which makes the direction of the spin difficult to determine in cases where the rate is relatively slow) is inverse to the intuitive spin, meaning the 'arms' of the spiral are actually leading arms, not trailing arms. Simultaneously this implies that the galaxy is not 'pulling' anything from its surrounding region, but pushing into its surrounding region. For a galaxy to endure for any length of time, therefore, the galaxy must be producing, rather than consuming, matter and energy in some way. This also fits with the observation that spiral galaxies, unlike other types which appear to be older, tend to be more isolated, further from the dense clusters of other types of galaxies. Were they to exist fundamentally by pulling things in from the surrounding area, one would expect them to be more prevalent where there was more in the surrounding area to draw in. Leaving aside the unanswered question of what the 'arms' actually consist of (the intuition that they consist of denser areas of stars is also incorrect – the orbits of stars around the galactic core are extremely eccentric in general, and don't correspond to the 'arms' in any way, thus in a few hundred thousand years, the sun is predicted to be much closer to the galactic core, but outside any of the arms –

- by Andrew Glynn
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- Quantum Physics, Cosmology (Physics), Gravitation, Particle Physics
- by Evan Skillman
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- Organic Chemistry, Star Formation, Dwarf Galaxies, Starburst Galaxies