Global and Local Infall in the ASHES Sample (GLASHES). III. Physical Parameters of Contracting Motion onto Dense Cores in 70 mu m Dark Massive Clumps

summary

Video file (mp4)

The gist

The gist: The study presents infall velocities and mass infall rates derived from blue-asymmetric line profiles toward cores embedded in massive 70 µm-dark clumps, providing the first statistical

In short

This study used ALMA observations to measure infall velocities and mass infall rates toward dense cores within massive 70 µm-dark clumps. They found systematic increases in these accretion rates with core mass and evolutionary stage, suggesting that organized external gas infall is a key process driving the growth of high-mass stars from early dense fragments.

Key concepts

Hill5 Model
An analytic radiative transfer model used to fit the asymmetric line profiles of molecular emission from collapsing cores. It uses five parameters—including infall velocity ($v_{ m in}$), optical depth ($ au$), and temperature ($T_{ m peak}$)—to describe how gas moves inward and heats up as it collapses toward the core center.
Infall Velocity ($v_{ m in}$)
The speed at which gas is falling onto a dense core. The study found these velocities range from 0.11 to 1.60 km s$^{-1}$, which are close to the cores' free-fall velocities, indicating that the contraction is dynamically fast and organized.
Mass Infall Rate ($\dot{M}$)
The rate at which mass is accumulating onto a core per unit time. This rate scales with core mass following a power law ($\dot{M} \propto M^{0.83}$). The study found rates ranging from $\sim10^{-5}$ to $5\times10^{-3}\ M_{\odot}\ yr^{-1}$, which are crucial for understanding core growth.
Hierarchical Accretion
The idea that gas accumulates in a step-wise manner, starting from large molecular clouds down to dense cores. This study supports a 'clump-fed' scenario where individual cores are continuously replenished by infall from the surrounding larger clump, rather than just accreting from their immediate surroundings.

Terminology used across episodes

This episode discusses

The paper

Global and Local Infall in the ASHES Sample (GLASHES). III. Physical Parameters of Contracting Motion onto Dense Cores in 70 mu m Dark Massive Clumps · Read on arXiv

Kaho Morii, Patricio Sanhueza, Qizhou Zhang, Philip C. Myers, James M. Jackson, Fumiaki Yoshida

Center for Astrophysics | Harvard & Smithsonian · Department of Astronomy, School of Science, The University of Tokyo · Green Bank Observatory

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera, and with me are Jocelyn and Subrahmanyan, guest researcher.

Jocelyn: Today's paper: "Global and Local Infall in the ASHES Sample (GLASHES). III. Physical Parameters of Contracting Motion onto Dense Cores in 70 mu m Dark Massive Clumps".

Vera: The gist: The study presents infall velocities and mass infall rates derived from blue-asymmetric line profiles toward cores embedded in massive 70 µm-dark clumps,

Jocelyn: First, who's behind it and why it matters.

Paper summary: Vera: So, to recap where we are: we know these cores are showing infall motions that scale with their evolution. Now, let's look at the specifics of this paper "Global and Local Infall in the ASHES Sample (GLASHES). III. Physical Parameters of Contracting Motion onto Dense Cores in seventy mu m Dark Massive Clumps <ref:2610.10676#pg1,Physical Parameters of Contracting Motion onto Dense Cores in 70>."

Jocelyn: This paper focuses on using blue-asymmetric line profiles from those cores embedded in massive seventy mu m-dark clumps to derive the infall velocities and mass infall rates <ref:2610.10676#pg1,infall velocities and mass infall rates>. The core thesis is that these measurements give us the first statistical constraints on how mass accumulates at the core scale during the very early stages of high-mass star formation.

Subrahmanyan: Why does that matter? Because for a long time, we've debated whether most of the final stellar mass comes from gas already bound in the core, or if it’s being accreted from much larger surrounding clumps. This work provides data that helps us distinguish between those two scenarios at this earliest stage.

Vera: The paper found that when they apply a Hill5 model to seventy of the one hundred thirty-five cores with blue-asymmetric profiles, they got infall velocities between zero point one one and one point six zero km s−one and mass infall rates spanning from about ten-five to five times ten-three solar masses per year.

Jocelyn: And they noted that these quantities are not static; the velocity and the rate both go up as we move from prestellar candidates through warm cores and into those outflow-associated cores. That's a strong signal for something dynamic happening during core evolution.

Subrahmanyan: The paper also found that these inferred infall velocities are close to what you expect from free-fall velocities—the mean v in over free-fall velocity is about zero point seven five—and the time it takes for this infall, t in, is comparable to the free-fall time. That points toward dynamically fast contraction within these cores.

Vera: And they tied this motion to the turbulence, finding that organized infall actually correlates moderately with both the non-thermal velocity dispersion and Mach number measured from optically thin tracers. This suggests that this ordered infall contributes to those observed line widths, not just random turbulence.

Conclusion: Vera: So, wrapping up this discussion on "Global and Local Infall in the ASHES Sample (GLASHES). III. Physical Parameters of Contracting Motion onto Dense Cores in seventy mu m Dark Massive Clumps," we have established that these massive seventy mu m-dark clumps are already exhibiting organized infall motions whose strength changes with the core's mass and its stage of evolution <ref:2610.10676#pg1,Physical Parameters of Contracting Motion onto Dense Cores in 70>.

Jocelyn: The implications here are that we can now set some statistical constraints on how mass actually accumulates at the core level when high-mass stars are just beginning to form. It shows that this process is happening right from these dense structures, not much later on.

Subrahmanyan: What this means for the bigger picture is that it supports a hierarchical, clump-fed picture where core-scale accretion is continuously replenished by material falling in from those larger clumps. The early stage involves dense fragments seeding future stars and growing immediately through external infall at rates around ten-four solar masses per year.

Vera: We also see a clear trend in the mass infall rate scaling with core mass, following a power-law relation where = one point three times ten-four (M/M) zero point eight three plus or minus zero point zero six across cores between about zero point one M and thirty M.

Jocelyn: And that power-law index itself changes, moving from about zero point six five for prestellar cores to about one point one zero for those outflow-associated cores, which suggests a transition in the dominant accretion mechanism as the core evolves.

Subrahmanyan: The paper also notes a limitation: they can't fully quantify geometry and projection effects because of current angular resolution, and the inferred infall velocities depend on which specific Hill5 model you choose to use.

Vera: So, while this work gives us solid data on the physical parameters of contracting motion, we still need higher resolution observations to nail down those density profiles accurately. But it’s a strong benchmark for what we expect in these very early phases of high-mass star formation.

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