Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations, and therefore are studied intensively for details of the formation of protoplanetary disks within protostellar envelopes. At millimetre wavelengths, kinematic signatures of collapse have been observed in several such protostars, through observations of molecular lines that probe their outer envelopes. It has been suggested that one or more components of the proto-multiple system NGC 1333–IRAS 4 (refs 1, 2) may display signs of an embedded region that is warmer and denser than the bulk of the envelope3,4. Here we report observations that reveal details of the core on Solar System dimensions. We detect in NGC 1333–IRAS 4B a rich emission spectrum of H2O, at wavelengths 20–37 μm, which indicates an origin in extremely dense, warm gas. We can model the emission as infall from a protostellar envelope onto the surface of a deeply embedded, dense disk, and therefore see the development of a protoplanetary disk. This is the only example of mid-infrared water emission from a sample of 30 class 0 objects, perhaps arising from a favourable orientation; alternatively, this may be an early and short-lived stage in the evolution of a protoplanetary disk.
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This work was supported in part by NASA through the Spitzer-IRS Instrument Team, Origins and Astrobiology programmes, and by CONACyT (México). We are grateful to R. Gutermuth for use of the Spitzer-IRAC data on NGC 1333, and to M. Jura, L. Keller, G. Sloan and D. Hollenbach for discussions.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
This file contains Supplementary Discussion to which the main-body text refers, Supplementary Tables 1-2 and Supplementary Figures 1-2 with Legends. Supplementary Figure S1 shows the rotational energy level diagram of water and Supplementary Figure 2 is a large rendition of the high-resolution spectra of NGC 1333 IRAS4B and the model of this object, with all spectral features identified. (PDF 221 kb)
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Watson, D., Bohac, C., Hull, C. et al. The development of a protoplanetary disk from its natal envelope. Nature 448, 1026–1028 (2007). https://doi.org/10.1038/nature06087