Magnetic fields in the early stages of massive star formation as
  revealed by ALMA
  We present 1.3 mm ALMA dust polarization observations at a resolution of
$\sim$0.02 pc of three massive molecular clumps, MM1, MM4, and MM9, in the
infrared dark cloud G28.34+0.06. With the sensitive and high-resolution
continuum data, MM1 is resolved into a cluster of condensations. The magnetic
field structure in each clump is revealed by the polarized emission. We found a
trend of decreasing polarized emission fraction with increasing Stokes $I$
intensities in MM1 and MM4. Using the angular dispersion function method (a
modified Davis-Chandrasekhar-Fermi method), the plane-of-sky magnetic field
strength in two massive dense cores, MM1-Core1 and MM4-Core4, are estimated to
be $\sim$1.6 mG and $\sim$0.32 mG, respectively. \textbf{The ordered magnetic
energy is found to be smaller than the turbulent energy in the two cores, while
the total magnetic energy is found to be comparable to the turbulent energy.}
The total virial parameters in MM1-Core1 and MM4-Core4 are calculated to be
$\sim$0.76 and $\sim$0.37, respectively, suggesting that massive star formation
does not start in equilibrium. Using the polarization-intensity gradient-local
gravity method, we found that the local gravity is closely aligned with
intensity gradient in the three clumps, and the magnetic field tends to be
aligned with the local gravity in MM1 and MM4 except for regions near the
emission peak, which suggests that the gravity plays a dominant role in
regulating the gas collapse. Half of the outflows in MM4 and MM9 are found to
be aligned within 10$^{\circ}$ of the condensation-scale ($<$0.05 pc) magnetic
field, indicating that the magnetic field could play an important role from
condensation to disk scale in the early stage of massive star formation. We
also found that the fragmentation in MM1-Core1 cannot be solely explained by
thermal Jeans fragmentation or turbulent Jeans fragmentation.
