* Astronomy

Blobrana · L

RE: Cepheus A HW2

Blobrana · L

A team of astronomers, led by Dr. Wouter Vlemmings at Bonn University, has used the MERLIN radio telescope network centred on the Jodrell Bank Observatory to show that magnetic fields play an important role during the birth of massive stars. Magnetic fields are already known to strongly influence the formation of lower-mass stars like our Sun. This new study reveals that the way in which high-mass and low-mass stars form may be more similar than previously suspected. The scientists report their work in the journal Monthly Notices of the Royal Astronomical Society.
Massive stars, more than 8 times the mass of the Sun, are crucial to the formation of other stars, planets and even life. Though rare, they dominate the content and evolution of the interstellar material in the Galaxy and are responsible for the production of heavy elements such as iron. However, the question of how massive stars are formed has proved extremely difficult to answer. The role of magnetic fields in particular has been a topic of great debate. Many scientists thought that radiation and turbulence would be the more dominant factors, and hence their formation process would be significantly different from that of less massive stars such as our Sun.
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Blobrana · L

Title: Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2
Authors: W.H.T. Vlemmings, G. Surcis, K.J.E. Torstensson, H.J. van Langevelde

We present polarisation observations of the 6.7-GHz methanol masers around the massive protostar Cepheus A HW2 and its associated disc. The data were taken with the Multi-Element Radio Linked Interferometer Network. The maser polarization is used to determine the full three-dimensional magnetic field structure around Cepheus A HW2. The observations suggest that the masers probe the large scale magnetic field and not isolated pockets of a compressed field. We find that the magnetic field is predominantly aligned along the protostellar outflow and perpendicular to the molecular and dust disc. From the three-dimensional magnetic field orientation and measurements of the magnetic field strength along the line of sight, we are able to determine that the high density material, in which the masers occurs, is threaded by a large scale magnetic field of ~23 mG. This indicates that the protostellar environment at ~1000 AU from Cepheus A HW2 is slightly supercritical (lambda approximately 1.7) and the relation between density and magnetic field is consistent with collapse along the magnetic field lines. Thus, the observations indicate that the magnetic field likely regulates accretion onto the disc. The magnetic field dominates the turbulent energies by approximately a factor of three and is sufficiently strong to be the crucial component stabilising the massive accretion disc and sustaining the high accretion rates needed during massive star-formation.

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