The magnetic field structure of a star-forming Bok globule BHR 71 was determined based on near-infrared polarimetric observations of background stars .
The magnetic field in BHR 71 was mapped from 25 stars .
By using a simple 2D parabolic function , the plane-of-sky magnetic axis of the core was found to be \theta _ { mag } = 125 ^ { \circ } \pm 11 ^ { \circ } .
The plane-of-sky mean magnetic field strength of BHR 71 was found to be B _ { pos } = 8.8 - 15.0 \mu G , indicating that the BHR 71 core is magnetically supercritical with \lambda = 1.44 - 2.43 .
Taking into account the effect of thermal/turbulent pressure and the plane-of-sky magnetic field component , the critical mass of BHR 71 was M _ { cr } = 14.5 - 18.7 M _ { \odot } , which is consistent with the observed core mass of M _ { core } \approx 14.7 M _ { \odot } ( Yang et al .
2017 ) .
We conclude that BHR 71 is in a condition close to a kinematically critical state , and the magnetic field direction lies close to the plane of sky .
Since BHR 71 is a star-forming core , a significantly subcritical condition ( i.e. , the magnetic field direction deviating from the plane of sky ) is unlikely , and collapsed from a condition close to a kinematically critical state .
There are two possible scenarios to explain the curved magnetic fields of BHR 71 , one is an hourglass-like field structure due to mass accumulation and the other is the Inoue & Fukui ( 2013 ) mechanism , which proposes the interaction of the core with a shock wave to create curved magnetic fields wrapping around the core .