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Inside–Out Planet Formation (IOPF) is a theory addressing the origin of Systems of Tightly-Packed Inner Planets (STIPs) via in situ formation and growth of the planets. It predicts that a pebble ring is established at the pressure maximum associated with the dead zone inner boundary (DZIB) with an inner disc magnetorotational instability (MRI)-active region. Using direct N -body simulations, we study the collisional evolution of planetesimals formed from such a pebble ring, in particular, examining whether a single dominant planet emerges. We consider a variety of models, including some in which the planetesimals are continuing to grow via pebble accretion. We find that the planetesimal ring undergoes oligarchic evolution, and typically turns into 2 or 3 surviving oligarchs on nearly coplanar and circular orbits, independent of the explored initial conditions or form of pebble accretion. The most massive oligarchs typically consist of about |$70{{\ \rm per\ cent}}$| of the total mass, with the building-up process typically finishing within ∼105 yr. However, a relatively massive secondary planet always remains with |$\sim 30\!-\!65{{\ \rm per\ cent}}$| of the mass of the primary. Such secondary planets have properties that are inconsistent with the observed properties of the innermost pairs of planets in STIPs. Thus, for IOPF to be a viable theory for STIP formation, it needs to be shown how oligarchic growth of a relatively massive secondary from the initial pebble ring can be avoided. We discuss some potential additional physical processes that should be included in the modelling and explored as next steps. [ABSTRACT FROM AUTHOR]

We investigate the dynamical evolution of star clusters during their formation, assuming that they are born from a turbulent starless clump of a given mass that is embedded within a parent self-gravitating molecular cloud characterized by a particular mass surface density. In contrast to the standard practice of most N -body studies, we do not assume that all stars are formed at once. Rather, we explore the effects of different star formation rates on the global structure and evolution of young embedded star clusters, also considering various primordial binary fractions and mass segregation levels. Our fiducial clumps studied in this paper have initial masses of |$M_{\rm cl} = 3000\, M_\odot$|⁠, are embedded in ambient cloud environments of Σcloud = 0.1 and 1 g cm−2, and gradually form stars with an overall efficiency of 50 per cent until the gas is exhausted. We investigate star formation efficiencies per free-fall time in the range εff = 0.01–1, and also compare to the instantaneous case (εff = ∞) of Paper I. We show that most of the interesting dynamical processes that determine the future of the cluster, happen during the early formation phase. In particular, the ejected stellar population is sensitive to the duration of star cluster formation: for example, clusters with longer formation times produce more runaway stars, since these clusters remain in a dense state for longer, thus favouring occurrence of dynamical ejections. We also show that the presence of radial age gradients in star clusters depends sensitively on the star formation efficiency per free-fall time, with observed values being matched best by our slowest forming clusters with εff ≲ 0.03. [ABSTRACT FROM AUTHOR]

We calculate cosmic distributions in space and time of the formation sites of the first, 'Pop III.1' stars, exploring a model in which these are the progenitors of all supermassive black holes (SMBHs), seen in the centres of most large galaxies. Pop III.1 stars are defined to form from primordial composition gas in dark matter minihaloes with |${\sim }10^6\, \mathrm{M}_\odot$| that are isolated from neighbouring astrophysical sources by a given isolation distance, d iso. We assume Pop III.1 sources are seeds of SMBHs, based on protostellar support by dark matter annihilation heating that allows them to accrete a large fraction of their minihalo gas, i.e. |${\sim }10^5\, \mathrm{M}_\odot$|⁠. Exploring d iso from 10 to |$100\, \rm {kpc}$| (proper distances), we predict the redshift evolution of Pop III.1 source and SMBH remnant number densities. The local, |$z$|  = 0 density of SMBHs constrains |$d_{\rm {iso}}\lesssim 100\, \rm {kpc}$| (i.e. |$3\, \rm {Mpc}$| comoving distance at |$z$| ≃ 30). In our simulated (⁠|${\sim }60\, \rm {Mpc})^3$| comoving volume, Pop III.1 stars start forming just after |$z$|  = 40. Their formation is largely complete by |$z$| ≃ 25–20 for d iso = 100– |$50\, \rm {kpc}$|⁠. We follow source evolution to |$z$|  = 10, by which point most SMBHs reside in haloes with |${\gtrsim }10^8\, \mathrm{M}_\odot$|⁠. Over this period, there is relatively limited merging of SMBHs for these values of d iso. We also predict SMBH clustering properties at |$z$|  = 10: feedback suppression of neighbouring sources leads to relatively flat angular correlation functions. [ABSTRACT FROM AUTHOR]

The luminosities of the centres of nearby elliptical galaxies are very low compared to models of thin disc accretion on to their black holes at the Bondi rate, typically a few hundredths to a few tenths of a solar mass per year. This has motivated models of inefficiently radiated accretion that invoke weak electron–ion thermal coupling, and/or inhibited accretion rates due to convection or outflows. Here we point out that, even if such processes are operating, a significant fraction of the accreting gas is prevented from reaching the central black hole because it condenses into stars in a gravitationally unstable disc. Star formation occurs inside the Bondi radius (typically ∼100 pc in giant ellipticals), but still relatively far from the black hole in terms of Schwarzschild radii. Star formation depletes and heats the gas disc, eventually leading to a marginally stable, but much reduced, accretion flow to the black hole. We predict the presence of cold (∼100 K), dusty gas discs, containing clustered Hα emission and occasional Type II supernovae, both resulting from the presence of massive stars. Star formation accounts for several features of the M87 system: a thin disc, traced by Hα emission, is observed on scales of about 100 pc, with features reminiscent of spiral arms and dust lanes; the star formation rate inferred from the intensity of Hα emission is consistent with the Bondi accretion rate of the system. Star formation may therefore help to suppress accretion on to the central engines of massive ellipticals. We also discuss some implications for the fuelling of the Galactic Centre and quasars. [ABSTRACT FROM AUTHOR]