Dust grains cannot grow to millimeter sizes in protostellar envelopes

TL;DR

This paper demonstrates analytically that millimeter-sized dust grains cannot form in protostellar envelopes under standard coagulation assumptions, challenging previous interpretations of dust observations.

Contribution

It provides a theoretical proof that in-situ grain growth to millimeter sizes is impossible in protostellar envelopes under typical conditions.

Findings

Millimeter-sized grains cannot form in protostellar envelopes via standard coagulation.

Observed millimeter emission may originate from pre-existing grains or other processes.

The results challenge current interpretations of dust growth in early star formation stages.

Abstract

A big question in the field of star and planet formation is the time at which substantial dust grain growth occurs. The observed properties of dust emission across different wavelength ranges have been used as an indication that millimeter-sized grains are already present in the envelopes of young protostars. However, this interpretation is in tension with results from coagulation simulations, which are not able to produce such large grains in these conditions. In this work, we show analytically that the production of millimeter-sized grains in protostellar envelopes is impossible under the standard assumptions about the coagulation process. We discuss several possibilities that may serve to explain the observed dust emission in the absence of in-situ grain growth to millimeter sizes.