Magnetic fields found in a jet from a baby star

An international research team led by Chin-Fei Lee in the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has made a breakthrough observation with the Atacama Large Millimeter/submillimeter Array (ALMA), confirming the presence of magnetic fields in a jet from a protostar. Jets are believed to play an important role in star formation, enabling the protostar to accrete mass from an accretion disk by removing angular momentum from the disk. It is highly supersonic and collimated, and predicted in theory to be launched and collimated by magnetic fields. The finding supports the theoretical prediction and confirms the role of the jet in star formation.

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Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al

Figure 1: ALMA detection of SiO line polarization in the HH 211 jet. (Top) A composite image showing the HH 211 jet and the outflow around it. The blue and red images show respectively the approaching (blueshifted) side and the receding (redshifted) side of the jet in SiO (adopted from Lee et al. 2009).

Gray image shows the outflow in H2 (adopted from Hirano et al. 2006). (Bottom) A zoom-in to the innermost part of the jet within 700 au of the central protostar. Orange image shows the accretion disk recently detected with ALMA (Lee et al. 2018).

Blue and red images show the blueshifted and redshifted sides of the innermost jet coming out from the disk, obtained in our observation.

Yellow line segments show the orientations of the SiO line polarization in the jet.

A size scale of our solar system is shown in the lower right corner for size comparison. In the two panels, asterisks mark the possible position of the central protostar.

Source / Image Courtesy

Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.

Figure 2: Possible helical magnetic fields in the HH 211 jet. Blue and red images show the blueshifted and redshifted sides of the jet coming out from the disk, as shown in the bottom panel of Figure 1.

The greenish helical lines show the possible magnetic field morphology in the jet.

The asterisk marks the possible position of the central protostar. A size scale of our solar system is shown in the lower right corner for size comparison.

Source / Image Courtesy

HH 211 is a well-defined jet from one of the youngest protostellar systems in Perseus at a distance of about 1,000 light-years.

The central powering protostar has an age of only about 10,000 yrs (which is about 2 millionths of the age of our Sun) and a mass of about 0.05 solar mass.

The jet is rich in SiO molecular gas and drives a spectacular molecular outflow around it (see the top panel in Figure 1).

Researchers using NASA's Kepler space telescope have found evidence of strong magnetic fields in the cores of stars--a finding that could upset theories of stellar evolution.