Gas Accretion to the Jovian Planet in the Protoplanetary Disk

AbstractThe “Grand Tack” model proposes that the inner Solar System was sculpted by the giant planets' orbital migration in the gaseous protoplanetary disk. Jupiter first migrated inward then Jupiter and Saturn migrated back outward together. If Jupiter's turnaround or “tack” point was at ~ 1.5 AU the inner disk of terrestrial building blocks would have been truncated at ~ 1 AU, naturally producing the terrestrial planets' masses and spacing. During the gas giants' migration the asteroid belt is severely depleted but repopulated by distinct planetesimal reservoirs that can be associated with the present-day S and C types. The giant planets' orbits are consistent with the later evolution of the outer Solar System.Here we confront common criticisms of the Grand Tack model. We show that some uncertainties remain regarding the Tack mechanism itself; the most critical unknown is the timing and rate of gas accretion onto Saturn and Jupiter. Current isotopic and compositional measurements of Solar System bodies – including the D/H ratios of Saturn's satellites – do not refute the model. We discuss how alternate models for the formation of the terrestrial planets each suffer from an internal inconsistency and/or place a strong and very specific requirement on the properties of the protoplanetary disk.We conclude that the Grand Tack model remains viable and consistent with our current understanding of planet formation. Nonetheless, we encourage additional tests of the Grand Tack as well as the construction of alternate models.

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Stopping Super-Earths from growing into Jupiters

10.5194/epsc2020-506 ◽

2020 ◽

Author(s):

Mohamad Ali-Dib ◽

Andrew Cumming ◽

Doug Lin

Keyword(s):

Planet Formation ◽

Thermal State ◽

Relative Size ◽

Protoplanetary Disk ◽

Outer Envelope ◽

Dominant Type ◽

Lower Entropy ◽

Gas Accretion ◽

The Hill

Super-Earths are by far the most dominant type of exoplanet, yet their formation is still not well understood. In particular, planet formation models predict that many of them should have accreted enough gas to become gas giants. Here we examine the role of the protoplanetary disk in the cooling and contraction of the protoplanetary envelope. In particular, we investigate the effects of 1) the thermal state of the disk as set by the relative size of heating by accretion or irradiation, and whether its energy is transported by radiation or convection, and 2) advection of entropy into the outer envelope by disk flows that penetrate the Hill sphere, as found in 3D global simulations. We find that, at 0.1 AU, the envelope quickly becomes fully radiative, nearly isothermal, and thus cannot cool down, stalling gas accretion. This effect is significantly more pronounced in convective disks, leading to envelope mass or- ders of magnitude lower. Entropy advection at 0.1 AU in either radiative or convective disks could therefore explain why super-Earths failed to undergo runaway accretion. Ali-Dib, Cumming, & Lin (MNRAS 2020)

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The paradox of youth for ALMA planet candidates

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa246 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2910-2925 ◽

Cited By ~ 1

Author(s):

S Nayakshin

Keyword(s):

Planet Formation ◽

Large Population ◽

Giant Planets ◽

Optical Observations ◽

Dusty Gas ◽

Radial Migration ◽

Alternative Scenario ◽

Gaseous Mass ◽

Gas Accretion ◽

Jovian Planet

ABSTRACT Recent ALMA observations indicate that the majority of bright protoplanetary discs show signatures of young moderately massive planets. I show that this result is paradoxical. The planets should evolve away from their observed states by radial migration and gas accretion in about 1 per cent of the system age. These systems should then hatch tens of giant planets in their lifetime, and there should exist a very large population of bright planet-less discs; none of this is observationally supported. An alternative scenario, in which the population of bright ALMA discs is dominated by secondary discs recently rejuvenated by deposition of new gas, is proposed. The data are well explained if the gaseous mass of the discs is comparable to a Jovian planet mass, and they last a small fraction of a Million years. Self-disruptions of dusty gas giant protoplanets, previously predicted in the context of the Tidal Downsizing theory of planet formation, provide a suitable mechanism for such injections of new fuel, and yield disc and planet properties commensurate with ALMA observations. If this scenario is correct, then the secondary discs have gas-to-dust ratios considerably smaller than 100, and long look ALMA and NIR/optical observations of dimmer targets should uncover dusty, not yet disrupted, gas clumps with sizes of order an au. Alternatively, secondary discs could originate from late external deposition of gas into the system, in which case we expect widespread signatures of warped outer discs that have not yet come into alignment with the planets.

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Effects of initial density profiles on massive star cluster formation in giant molecular clouds

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab491 ◽

2021 ◽

Author(s):

Yingtian Chen ◽

Hui Li ◽

Mark Vogelsberger

Keyword(s):

Angular Momentum ◽

Star Formation ◽

Molecular Clouds ◽

Globular Clusters ◽

Cluster Formation ◽

Initial Density ◽

Giant Molecular Clouds ◽

Density Profiles ◽

Stellar Feedback ◽

Gas Accretion

Abstract We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ‘hierarchically’ to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ‘accretion’ mode from centrally-concentrated clouds in the early Universe.

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Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab402 ◽

2021 ◽

Author(s):

Arpan Das ◽

Dominik R G Schleicher ◽

Nathan W C Leigh ◽

Tjarda C N Boekholt

Keyword(s):

Black Holes ◽

Initial Conditions ◽

High Redshift ◽

Star Clusters ◽

Gas Reservoir ◽

Highly Sensitive ◽

Stellar Collisions ◽

Key Variables ◽

Chaotic Nature ◽

Gas Accretion

Abstract More than two hundred supermassive black holes (SMBHs) of masses ≳ 109 M⊙ have been discovered at z ≳ 6. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses ∼103 − 5 M⊙ into seed black holes which could grow upto few times 109 M⊙ SMBHs observed at z ∼ 7. In this paper, we explore how SMSs with masses ∼103 − 5 M⊙ could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs) using idealised N-body simulations. We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, SMSs of masses ∼103 − 5 M⊙ can form for all three accretion scenarios considered in this work.

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Efficiency of thermal conduction in a magnetized circumgalactic medium

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab110 ◽

2021 ◽

Vol 502 (1) ◽

pp. 1263-1278

Author(s):

Richard Kooij ◽

Asger Grønnow ◽

Filippo Fraternali

Keyword(s):

Magnetic Field ◽

Thermal Conduction ◽

Large Temperature ◽

Gas Condensation ◽

Circumgalactic Medium ◽

Field Lines ◽

Gas Accretion ◽

Cloud Evolution ◽

The Magnetic Field ◽

Cold Gas

ABSTRACT The large temperature difference between cold gas clouds around galaxies and the hot haloes that they are moving through suggests that thermal conduction could play an important role in the circumgalactic medium. However, thermal conduction in the presence of a magnetic field is highly anisotropic, being strongly suppressed in the direction perpendicular to the magnetic field lines. This is commonly modelled by using a simple prescription that assumes that thermal conduction is isotropic at a certain efficiency f < 1, but its precise value is largely unconstrained. We investigate the efficiency of thermal conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of cold clouds moving through a hot medium, using artificially suppressed isotropic thermal conduction (with f), against 3D magnetohydrodynamical (MHD) simulations with (true) anisotropic thermal conduction. Our main diagnostic is the time evolution of the amount of cold gas in conditions representative of the lower (close to the disc) circumgalactic medium of a Milky-Way-like galaxy. We find that in almost every HD and MHD run, the amount of cold gas increases with time, indicating that hot gas condensation is an important phenomenon that can contribute to gas accretion on to galaxies. For the most realistic orientations of the magnetic field with respect to the cloud motion we find that f is in the range 0.03–0.15. Thermal conduction is thus always highly suppressed, but its effect on the cloud evolution is generally not negligible.

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Detecting the halo heating from AGN feedback with ALMA

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2945 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5134-5146 ◽

Cited By ~ 2

Author(s):

S Brownson ◽

R Maiolino ◽

M Tazzari ◽

S Carniani ◽

N Henden

Keyword(s):

Star Formation ◽

Correction Factor ◽

Spatial Scales ◽

Complex Structure ◽

Host Galaxy ◽

Cosmological Simulations ◽

Beam Attenuation ◽

Gas Accretion ◽

Marginal Detection ◽

Compact Sources

ABSTRACT The Sunyaev–Zel’dovich (SZ) effect can potentially be used to investigate the heating of the circumgalactic medium and subsequent suppression of cold gas accretion on to the host galaxy caused by quasar feedback. We use a deep ALMA observation of HE0515-4414 in band 4, the most luminous quasar known at the peak of cosmic star formation (z = 1.7), to search for the SZ signal tracing the heating of the galaxy’s halo. ALMA’s sensitivity to a broad range of spatial scales enables us to disentangle emitting compact sources from the negative, extended SZ signal. We obtain a marginal SZ detection (∼3.3σ) on scales of about 300 kpc (30–40 arcsec), at the 0.2 mJy level, 0.5 mJy after applying a correction factor for primary beam attenuation and flux that is resolved out by the array. We show that our result is consistent with a simulated ALMA observation of a similar quasar in the fable cosmological simulations. We emphasize that detecting an SZ signal is more easily achieved in the visibility plane than in the (inferred) images. We also confirm a marginal detection (3.2σ) of a potential SZ dip on smaller scales (<100 kpc) already claimed by other authors, possibly highlighting the complex structure of the halo heating. Finally, we use SZ maps from the fable cosmological simulations, convolved with ALMA simulations, to illustrate that band 3 observations are much more effective in detecting the SZ signal with higher significance, and discuss the optimal observing strategy.

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Interaction of solid bodies with atmospheres of protoplanets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001996 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 351-352

Author(s):

Ernst A. Dorfi ◽

Florian Ragossnig

Keyword(s):

Kinetic Energy ◽

Physical Properties ◽

Planet Formation ◽

Frictional Heating ◽

Protoplanetary Disk ◽

Small Bodies ◽

Early Stages ◽

Break Up ◽

Solid Bodies ◽

Stellar Source

AbstractDuring the early stages of planet formation accretion of small bodies add mass to the planet and deposit their energy kinetic energy. Caused by frictional heating and/or large stagnation pressures within the dense and extended atmospheres most of the in-falling bodies get destroyed by melting or break-up before they impact on the planet’s surface. The energy is added to the atmospheric layers rather than heating the planet directly. These processes can significantly alter the physical properties of protoplanets before they are exposed with their primordial atmospheres to the early stellar source when the protoplanetary disk becomes evaporated.

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Protoplanetary Disk Midplane

Encyclopedia of Astrobiology ◽

10.1007/978-3-642-27833-4_444-3 ◽

2014 ◽

pp. 1-1

Author(s):

Avi M. Mandell

Keyword(s):

Protoplanetary Disk

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Formation of supermassive black holes in galactic nuclei – I. Delivering seed intermediate-mass black holes in massive stellar clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab113 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2682-2700

Author(s):

Abbas Askar ◽

Melvyn B Davies ◽

Ross P Church

Keyword(s):

Black Holes ◽

Galactic Nuclei ◽

Supermassive Black Holes ◽

Stellar Clusters ◽

Orbital Eccentricity ◽

Intermediate Mass ◽

Stellar Cluster ◽

Wave Emission ◽

Gas Accretion ◽

Intermediate Mass Black Holes

ABSTRACT Supermassive black holes (SMBHs) are found in most galactic nuclei. A significant fraction of these nuclei also contains a nuclear stellar cluster (NSC) surrounding the SMBH. In this paper, we consider the idea that the NSC forms first, from the merger of several stellar clusters that may contain intermediate-mass black holes (IMBHs). These IMBHs can subsequently grow in the NSC and form an SMBH. We carry out N-body simulations of the simultaneous merger of three stellar clusters to form an NSC, and investigate the outcome of simulated runs containing zero, one, two, and three IMBHs. We find that IMBHs can efficiently sink to the centre of the merged cluster. If multiple merging clusters contain an IMBH, we find that an IMBH binary is likely to form and subsequently merge by gravitational wave emission. We show that these mergers are catalyzed by dynamical interactions with surrounding stars, which systematically harden the binary and increase its orbital eccentricity. The seed SMBH will be ejected from the NSC by the recoil kick produced when two IMBHs merge, if their mass ratio q ≳ 0.15. If the seed is ejected then no SMBH will form in the NSC. This is a natural pathway to explain those galactic nuclei that contain an NSC but apparently lack an SMBH, such as M33. However, if an IMBH is retained then it can seed the growth of an SMBH through gas accretion and tidal disruption of stars.

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