MADISON – A new, more accessible and much cheaper approach to surveying the topology and strength of interstellar magnetic fields – which weave through space in our galaxy and beyond, representing one of the most potent forces in nature – has been developed by researchers at the University of Wisconsin-Madison.
Together with gravity, magnetic fields play a major role in many of the astrophysical processes – from star formation to stirring the massive dust and gas clouds that permeate interstellar space – that underpin the structure and composition of stars, planets and galaxies. On the galactic scale, magnetic fields dominate the acceleration and propagation of cosmic rays, and play an important role in transferring heat and polarized radiation.
What’s more, the polarized radiation that arises from galactic magnetic fields exceeds by orders of magnitude that of the Cosmic Microwave Background (CMB), the relic radiation of the first moments of the universe. The next milestone in understanding the origin of the universe, some scientists believe, requires measuring the CMB’s polarized radiation. Importantly, unraveling the topology of the intervening magnetic fields between Earth and the CMB will be a necessary step to reliably obtain those data.
But despite their importance and pervasive influence, interstellar magnetic fields represent one of the final frontiers of astrophysics. Little is known about them, in large part, because they are exceedingly difficult to study.
“There are very limited ways to study magnetic fields in space,” explains Alexandre Lazarian, a UW-Madison professor of astronomy and an authority on the interstellar medium, the seemingly empty spaces between the stars that are, in fact, rich in matter and feature twisted, folded and tangled magnetic fields composed of fully or partially ionized plasmas entrained on magnetic fields. “Our understanding of all these (astrophysical) processes suffers from our poor knowledge of magnetic fields.”
Now, much of that knowledge may be more readily at hand. Writing this week (June 10, 2019) in the journal Nature Astronomy, an international team led by the Wisconsin astrophysicist demonstrates a new methodology capable of tracing the orientations of magnetic fields in the swirl of interstellar space.
The proof-of-concept reported in Nature Astronomy builds on a series of theoretical and numerical studies published over the last two years by Lazarian and his students, and which lay out a radical new approach to mapping the tangle of magnetic fields in space.
Until now, much of the detailed mapping of magnetic fields in diffuse environments such as clouds of dust and gas in space involved infrared polarimetry with instruments deployed either on satellites or balloons flown high in the stratosphere.
The new method, known as the Velocity Gradient Technique and informally as the “Wisconsin technique,” uses previously collected observational data from a variety of ground-based telescopes, transcending the need to put instruments in space, a costly and limited resource for astronomers. Building on studies of turbulence in magnetic fields in conducting fluids, Lazarian and his students devised the new statistical approach to measure the topology of magnetic fields using routine spectroscopic observations taken from the ground.