Earliest stages of star formation in Perseus

perseuscloud_hilborn2048Stardust in Perseus: image APOD, credit & copyright: Lynn Hilborn. The Perseus star-forming clouds contain objects which are candidates to be a first hydrostatic core (FHSC), theorized by Larson (1969) to be the very first stage of star formation, consisting mostly of molecular hydrogen and intermediate in evolutionary status between dense molecular cores known as “starless” and “pre-stellar”. Its lifetime is short, less than 30,000 yr. The subject was treated by Scientific American in 2010, the year one such object was found, Per-Bolo 58 (see abstract below). The region is the subject of much ongoing work with new surveys at (sub)-mm and longer wavelengths: see new work by Storm et al. (2016) for a very recent example.

The first hydrostatic core (FHSC) represents a very early phase in the low-mass star formation process, after collapse of the parent core has begun but before a true protostar has formed. This large (few AU), cool (100 K), pressure-supported core of molecular hydrogen is expected from theory, but has yet to be observationally verified. Here, we present observations of an excellent candidate for the FHSC phase: Per-Bolo 58, a dense core in Perseus that was previously believed to be starless. The 70 μm flux of 65 mJy, from new deep Spitzer MIPS observations, is consistent with that expected for the FHSC. A low signal-to-noise detection at 24 μm leaves open the possibility that Per-Bolo 58 could be a very low luminosity protostar, however. We utilize radiative transfer models to determine the best-fitting FHSC and protostar models to the spectral energy distribution and 2.9 mm visibilities of Per-Bolo 58. The source is consistent with an FHSC with some source of lower opacity through the envelope allowing 24 μm emission to escape; a small outflow cavity and a cavity in the envelope are both possible. While we are unable to rule out the presence of a protostar, if present it would be one of the lowest luminosity protostellar objects yet observed, with an internal luminosity of ~0.01 L .

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