# Massive and low-mass protostars in massive "starless" cores

## TL;DR

This study reveals that massive starless cores in IRDCs already host low- and high-mass protostars with outflows, indicating early stages of high-mass star formation often co-occurring with low-mass protostars.

## Contribution

It provides observational evidence that low-mass protostars form early within massive starless cores, challenging the notion that such cores are entirely starless.

## Key findings

- Massive cores host multiple outflows.
- Low-luminosity, massive cores are associated with early protostars.
- Low-mass protostars are present in early high-mass star formation stages.

## Abstract

The infrared dark clouds (IRDCs) G11.11$-$0.12 and G28.34$+$0.06 are two of the best-studied IRDCs in our Galaxy. These two clouds host clumps at different stages of evolution, including a massive dense clump in both clouds that is dark even at 70 and 100$\mu$m. Such seemingly quiescent massive dense clumps have been speculated to harbor cores that are precursors of high-mass stars and clusters. We observed these two "prestellar" regions at 1mm with the Submillimeter Array (SMA) with the aim of characterizing the nature of such cores. We show that the clumps fragment into several low- to high-mass cores within the filamentary structure of the enveloping cloud. However, while the overall physical properties of the clump may indicate a starless phase, we find that both regions host multiple outflows. The most massive core though 70 $\mu$m dark in both clumps is clearly associated with compact outflows. Such low-luminosity, massive cores are potentially the earliest stage in the evolution of a massive protostar. We also identify several outflow features distributed in the large environment around the most massive core. We infer that these outflows are being powered by young, low-mass protostars whose core mass is below our detection limit. These findings suggest that low-mass protostars have already formed or are coevally formed at the earliest phase of high-mass star formation.