Question What happens when we pass through Interstellar Clouds?

[Harry Costas]

The search for the origin of life is never-ending.

[Submitted on 12 Dec 2024]

Journey of complex organic molecules: Formation and transport in protoplanetary disks​

T. Benest Couzinou, O. Mousis, G. Danger, A. Schneeberger, A. Aguichine, A. Bouquet

Complex organic molecules serve as indicators of molecular diversity. Their detection on comets, planets, and moons has prompted inquiries into their origins, particularly the conditions conducive to their formation. One hypothesis suggests that the UV irradiation of icy grains in the protosolar nebula generates significant molecular complexity, a hypothesis supported by experiments on methanol ice irradiation. We investigated the irradiation of methanol ice particles as they migrate through the protosolar nebula. Our objective is to ascertain whether the encountered conditions facilitate the formation of complex organics molecules, and we leverage experimental data in our analysis. We developed a two-dimensional model that describes the transport of pebbles during the evolution of the protosolar nebula, employing a Lagrangian scheme. This model computes the interstellar UV flux received by the particles along their paths, which we compared with experimental values. On average, particles ranging from 1 to 100 micrometers in size, released at a local temperature of 20 K, undergo adequate irradiation to attain the same molecular diversity as methanol ice during the experiments within timescales of 25 kyr of protosolar nebula evolution. In contrast, 1 cm sized particles require 911 kyr of irradiation to reach similar molecular diversity, making comparable molecular complexity unlikely. Similarly, particles ranging from 1 to 100 micrometers in size, released at a local temperature of 80 K, receive sufficient irradiation after 141 and 359 kyr. The particles readily receive the irradiation dose necessary to generate the molecular diversity observed in the experiments within the outer regions of the disk. Our model, combined with future irradiation experiments, can provide additional insights into the specific regions where the building blocks of planets form.

 

[Harry Costas]

The more we keep researching, the more we can predict further movements.

[Submitted on 10 Feb 2024]

Rendez-vous with massive interstellar objects, as triggers of destabilisation​

Denis V. Mikryukov, Ivan I. Shevchenko

We study how close passages of interstellar objects of planetary and substellar masses may affect the immediate and long-term dynamics of the Solar system. We consider two nominal approach orbits, namely, the orbits of actual interstellar objects 1I/'Oumuamua and 2I/Borisov, assuming them to be typical or representative for interstellar swarms of matter. Thus, the nominal orbits of the interloper in our models cross the inner part of the Solar system. Series of massive numerical experiments are performed, in which the interloper's mass is varied with a small step over a broad range. We find that, even if a Jovian-mass interloper does not experience close encounters with the Solar system planets (and this holds for our nominal orbits), our planetary system can be destabilised on timescales as short as several million years. In what concerns substellar-mass interlopers (free-floating brown dwarfs), an immediate (on a timescale of ∼10−100 yr) consequence of such a MISO flyby is a sharp increase in the orbital eccentricities and inclinations of the outer planets. On an intermediate timescale (∼103−105 yr after the MISO flyby), Uranus or Neptune can be ejected from the system, as a result of their mutual close encounters and encounters with Saturn. On a secular timescale (∼106−107 yr after the MISO flyby), the perturbation wave formed by secular planetary interactions propagates from the outer Solar system to its inner zone.

 

[Harry Costas]

It doesn't seem very easy, but it comes with the territory.

[Submitted on 6 Jun 2024]

Gamma-ray burst interaction with the circumburst medium: The CBM phase of GRBs​

Asaf Pe'er, Felix Ryde

Progenitor stars of long gamma-ray bursts (GRBs) could be surrounded by a significant and complex nebula structure lying at a parsec scale distance. After the initial release of energy from the GRB jet, the jet will interact with this nebula environment. We show here that for a large, plausible parameter space region, the interaction between the jet blastwave and the wind termination (reverse) shock is expected to be weak, and may be associated with a precursor emission. As the jet blast wave encounters the contact discontinuity separating the shocked wind and the shocked interstellar medium, we find that a bright flash of synchrotron emission from the newly-formed reverse shock is produced. This flash is expected to be observed at around ~100 s after the initial explosion and precursor. Such a delayed emission thus constitutes a circumburst medium (CBM) phase in a GRB, having a physically distinct origin from the preceding prompt phase and the succeeding afterglow phase. The CBM phase emission may thus provide a natural explanation to bursts observed to have a precursor followed by an intense, synchrotron-dominated main episode that is found in a substantial minority, ~10% of GRBs. A correct identification of the emission phase is thus required to infer the properties of the flow and of the immediate environment around GRB progenitors.

 

[Harry Costas]

It's very interesting to those who keep on learning.

[Submitted on 26 Aug 2024]

Bursts of star formation and radiation-driven outflows produce efficient LyC leakage from dense compact star clusters​

Shyam H. Menon, Blakesley Burkhart, Rachel S. Somerville, Todd A. Thompson, Amiel Sternberg

The escape of LyC photons emitted by massive stars from the dense interstellar medium of galaxies is one of the most significant bottlenecks for cosmological reionization. The escape fraction shows significant scatter between galaxies, and anisotropic, spatial variation within them, motivating further study of the underlying physical factors responsible for these trends. We perform numerical radiation hydrodynamic simulations of idealized clouds with different gas surface densities (compactness) Σ∼102--105M⊙pc−2, meant to emulate star cluster-forming clumps ranging from conditions typical of the local Universe to the high ISM-pressure conditions more frequently encountered at high redshift. Our results indicate that dense compact star clusters with Σ≳104M⊙pc−2 efficiently leak LyC photons, with cloud-scale luminosity-weighted average escape fractions ≳80% as opposed to ≲10% for Σ∼100M⊙pc−2. This occurs due to higher star formation efficiencies and shorter dynamical timescales at higher Σ; the former results in higher intrinsic LyC emission, and the latter implies rapid evolution, with a burst of star formation followed by rapid gas dispersal, permitting high LyC escape well before the intrinsic LyC emission of stellar populations drop (∼4Myr). LyC escape in dense clouds is primarily facilitated by highly ionized outflows driven by radiation pressure on dust with velocities ∼3 times the cloud escape velocity. We also vary the (assumed) dust abundances (Zd) and find a very mild increase (∼10) in the escape fraction for ∼100 lower Zd. Our results suggest a scenario in which localized compact bursts of star formation in galaxies are disproportionately productive sites of LyC leakage.