IIA astronomers make breakthrough in understanding how cosmic dust grains line up with the galaxy’s magnetic field

A team of astronomers led by the Indian Institute of Astrophysics (IIA) and their collaborators have made a breakthrough in understanding how cosmic dust grains line up with the galaxy’s magnetic field.

Dust grains, typically a few micrometers in size and composed primarily of silicates and carbonaceous material, are found throughout the interstellar medium in the Milky Way and other galaxies.

These tiny particles play a crucial role in a wide range of astrophysical processes, including the formation of stars and planets.

The Department of Science and Technology said that this breakthrough by the astronomers provides the strongest observational evidence yet for the long-theorised ways in which dust aligns itself with magnetic fields in our Galaxy.

They focused on the massive star-forming infrared dark cloud G34.43+0.24, located around 12,000 light-years away in the Milky Way.

Using the POL-2 polarimeter on the James Clerk Maxwell Telescope in Hawaii, the researchers mapped how dust in this star-forming nursery aligned with magnetic fields.

The study found observational evidence for three different alignment mechanisms acting in a single cosmic cloud namely RAT-A, RAT-D and M-RAT.

RAT-A, implies RAdiative Torque Alignment in which non-spherical grains exposed to anisotropic radiation fields experience RAdiative Torques—RATs, that cause them to spin up and align with the direction of the surrounding magnetic fields.

RAT-D is Radiative Torque Disruption in which large dust grains spin so rapidly under strong radiation from the massive and luminous protostars embedded inside the cores that they are disrupted into smaller fragments, reducing the grain alignment efficiency and thereby lowering the polarization fraction.

M-RAT implies Magnetically-enhanced RAdiative Torque alignment mechanism in which alignment efficiency of grains is enhanced by strong magnetic relaxation strength of grains, resulting in higher polarization percentages.

“This shows that the grains respond differently depending on their environment—sometimes aligning perfectly, sometimes shattering under stress, and sometimes becoming super-efficient at tracing magnetic fields,” the department said.

It added that by proving how these mechanisms play out in real space, astronomers now have stronger tools to map magnetic fields across the galaxy.

“This work strengthens the observational support for the well-established popular grain alignment theories and makes a significant contribution to the long-standing quest to understand the exact grain alignment mechanisms,” said Saikhom Pravash, lead author and PhD researcher at IIA and Pondicherry University.