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The 7 mm Continuum Image of the Binary Protostellar System L1551 IRS 5

Image Credit: Lim and Takakuwa

The 7 mm continuum image of the binary protostellar system L1551 IRS 5 obtained with the VLA (Lim and Takakuwa 2006, ApJ, 653, 425).

Most stars are known to form as members of binary or multiple systems, but in ways that remain poorly understood. Here we show an image of the multiple protostellar system L1551 IRS5 made with a spatial resolution of ~5 AU at a wavelength of 7 mm using the Very Large Array (VLA) and Pie Town (PT) antenna of the Very Long Baseline Array (VLBA), both of the National Radio Astronomical Observatory (NRAO). This is the highest resolution image ever made of protostellar systems, and reveals with great clarity the properties of the L1551 IRS5 system. Previously thought to comprise two components, our image shows that L1551 IRS5 is instead a triple system (with each of the three components indicated by crosses). The two main components (which are aligned north-south) have cross-shaped structures, with one arm of each cross corresponding to a circumstellar dust disk, and the orthogonal arm to a bipolar ionized jet with orientation as indicated by the two pairs of arrows. The two circumstellar dust disks are aligned accurately parallel to each other, as well as to their surrounding disk-like condensation of molecular gas and dust. In addition, the clockwise orbital motion of these two components resembles the clockwise rotational motion of their surrounding condensation. These attributes constitute a smoking gun for the popular but hitherto unproven idea that multiple protostellar systems form via fragmentation in the central region of their parental condensations.