September 27, 2013
Critical Interplay Discovered Between Cosmic Dust, Magnetic Fields
Brett Smith for redOrbit.com - Your Universe Online
Interstellar magnetic fields can be found throughout the Milky Way and other similar galaxies. They are thought to be a key regulator in star formation and the propagation of cosmic rays.A new study published in The Astrophysical Journal has provided new insights for scientists looking to probe the strength and structure of these magnetic fields, a highly difficult phenomenon to accurately measure.
To learn more about interstellar magnetic fields, the team of astrophysicists looked to the behavior of cosmic dust, a key phase in the life cycle of stars. Interstellar dust particles can be between a few molecules to a micrometer in size. Sometimes coming from comets, asteroids or other sources, scientists determined in 2011 that deep space dust contains complex organic matter that could be generated quickly and naturally by stars.
By observing how this dust interacts with interstellar hydrogen and is oriented by the magnetic fields, study researchers were able to resolve a six-decade-long academic quandary.
The new study builds on a previous theory that suggest dust grains in interstellar space will spin and organize themselves in the presence of magnetic fields. The researchers said they expect their study about the polarization of interstellar dust to unclog a theoretical blockage – allowing for major advancements in the understanding of key elements of the interstellar medium and magnetic fields.
"We need to understand grain alignment if we want to make use of polarimetry as a means of investigating interstellar magnetic fields," said study author Alexandre Lazarian, a University of Wisconsin-Madison astrophysicist.
Scientists have known for decades that light becomes polarized as it passes through clouds of neatly aligned interstellar dust and have used observations of this polarized light as an observational technique.
"While interstellar polarization has been known since 1949, the physical mechanisms behind grain alignment have been poorly understood until recently," said co-author B-G Andersson of the Universities Space Research Association (USRA). "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."
According to theory, dust grains are spun by photons and their alignment is set along a magnetic field, observations of which point to a field’s orientation. Impurities on the dust grains allow for the formation of hydrogen molecules, which are consequently ejected, creating miniature "rocket engines.”
To confirm the theory, the study team investigated how the irregular grains of interstellar dust were set spinning in the first place. Observations conducted by Andersson showed that powerful molecular hydrogen formations along the surface of dust grains are a key factor in setting the dust grains spinning. The formation of hydrogen molecules generate reaction energy that the surfaces accept, setting the dust grains in motion.
The latest study, which was supported by the National Science Foundation, is especially timely because the ground-based Atacama Large Millimeter Array (ALMA) and the space-based Planck Telescope — are set to provide data capable of building onto the new results, Lazarian said.
Image Below: Intense molecular hydrogen formation shown in near infrared image of the reflection nebula IC 63 in the constellation Cassiopeia. The white bars represent polarization seen toward stars in the background of the nebula. The largest polarization shows the most intense emission, demonstrating that hydrogen formation influences alignment of the dust grain with a magnetic field. Credit: University of Wisconsin-Madison