Description
The study of dust grains in the earliest phases of star formation is crucial for understanding the chemical structure of dense cloud cores and the future evolution of solids in protoplanetary disks. It is however not clear if dust growth starts before star formation begins. Thus, we studied L1544, one of the most centrally concentrated prestellar cores on the verge of star formation, and with a well-known physical structure. Moreover, previous studies predict an increase in the dust opacity by a factor of 4 towards the center of L1544, which suggests dust grain coagulation towards its center. In order to test this theory, L1544 was observed using some of the newest continuum facilities: NIKA at the IRAM 30m telescope, MUSTANG-2 at the GBT and AzTEC at the LMT, observing at 1.2 and 2 mm, 3.3 mm, and 1.1 mm, respectively. The observations done at the IRAM 30m telescope show no indication of grain growth in this core. However, we show that the spatial resolution and the sensitivity of the observations are not sufficient for detecting the predicted effect, and that interferometers, such as ALMA, should be able to find evidence for grain growth in the inner 2000 au of the core. Newer results obtained with the maps observed at the GBT and the LMT show gradients in the dust opacity across the cloud, which is consistent with variations in the thickness of the ice mantles formed on the dust grains surfaces. These observations also show that previous models of the cloud need to be revised and include a new physical description of the cloud. A simple analytical grain growth model predicts the presence of grains of a few micrometers within the central 2000 au for the derived density and temperature profiles.
