Substellar-Mass Condensations in Prestellar Cores

TL;DR

This study uses combined submillimeter observations to reveal multiple dense condensations within prestellar cores, suggesting that star formation involves rapid condensation merging rather than simple core collapse.

Contribution

It provides high-resolution imaging evidence that prestellar cores contain multiple condensations with significant self-gravity, challenging standard star formation models.

Findings

Multiple condensations are present in prestellar cores.

Condensations have masses comparable to or larger than the critical Bonnor-Ebert mass.

Merging timescales are similar to gravitational collapse timescales.

Abstract

We present combined Submillimeter-Array (SMA) + single-dish images of the (sub)millimeter dust continuum emission toward two prestellar cores SM1 and B2-N5 in the nearest star cluster forming region, $\rho$ Ophiuchus. Our combined images indicate that SM1 and B2-N5 consist of three and four condensations, respectively, with masses of $10^{-2}-10^{-1}M_\odot$ and sizes of a few hundred AU. The individual condensations have mean densities of $10^8-10^9$ cm$^{-3}$ and the masses are comparable to or larger than the critical Bonner-Ebert mass, indicating that the self-gravity plays an important role in the dynamical evolution of the condensations. The coalescence timescale of these condensations is estimated to be about $10^4$ yr, which is comparable to the local gravitational collapse timescale, suggesting that merging of the condensations, instead of accretion, plays an essential role in the star formation process. These results challenge the standard theory of star formation, where a single, rather featureless prestellar core collapses to form at most a couple of condensations, each of which potentially evolves into a protostar that is surrounded by a rotating disk where planets are created.