Washington: Intense molecular hydrogen (H2) formation leads to an increase in the amount of polarization seen when starlight passes through dust clouds in the interstellar medium.
Universities Space Research Association ( USRA ) astronomer Dr. BG Andersson, said that while interstellar polarization has been known since 1949, the physical mechanisms behind grain alignment have been poorly understood until recently.
He said that these observations form part of a coordinated effort to - after more than 60 years - place interstellar grain alignment on a solid theoretical and observational footing.
Collaborating with the University of Wisconsin-Madison`s Professor Alexandre Lazarian, developer of the Radiative Alignment Torque (RAT) theory for grain alignment, and researchers from as far away as Hawaii and Finland, Andersson and Lazarian`s team used optical and near infrared polarimetry, high-accuracy optical spectroscopy and photometry, and sensitive imaging of a near infrared emission line of H2 for their studies.
By comparing their data to the predictions of RAT theory, the team was able to show that their observations agree with detailed theoretical models and to derive further specific predictions, which can be tested with additional observations.
The H2 molecule, the most common molecule in the universe, cannot form in the gas phase since the two atoms cannot get rid of the formation energy without a third body. Therefore, in 1948, Dutch astronomer Henrik van der Hulst proposed that H2 is formed on the surfaces of dust grains in the interstellar medium.
The fact that a connection is seen between H2 formation and grain alignment helps confirm that the formation of the molecule takes place on the surfaces of dust grains.
The study has been published in the Astrophysical Journal.