From NASA/DLR SOFIA : “Magnetic Chaos Hidden Within the Whirlpool Galaxy”



Alejandro Borlaff
Joan Schmelz

The Astrophysical Journal

Messier 51 Whirpool Galaxy Image via NASA/ESA S. Beckwith (STScI) the Hubble Heritage Team (STScI/AURA)

Hidden deep inside their spiral structure, an invisible force is affecting the evolution of galaxies — magnetic fields. Strong enough to regulate star formation and even drive gas into a supermassive black hole, magnetic fields might be one of the most important factors influencing how spiral galaxies evolve. In theory, the field could be affecting the global kinematics of the gas, modifying the rotation curve, and the redistribution of dense clouds of gas as they condense into stars. As a consequence, the magnetic fields might indirectly be forcing stars to migrate radially in the galactic disk. To detect these effects, it is necessary to map the shape of the magnetic fields in the cold, dense molecular clouds. However, traditional observations of magnetic fields made with radio telescopes are only sensitive to the diffuse interstellar gas that surrounds these star-forming regions, far away from where these fundamental effects might be taking place.

Thanks to SOFIA, scientists have finally been able to observe the morphology of the magnetic field inside the molecular gas of the grand design Whirlpool galaxy (Messier 51). The High-resolution Airborne Wideband Camera (HAWC+)(below) is able to map the magnetic fields deep in the cold, dark molecular clouds. The research team then compared these results with the magnetic field maps of the diffuse gas made with the Very Large Array in New Mexico and the Effelsberg radio telescope in Germany.

National Radio Astronomy Observatory(US)Karl G Jansky Very Large Array located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

Effelsberg Radio Telescope- a radio telescope in the Ahr Hills (part of the Eifel) in Bad Münstereifel(DE)

The magnetic field lines in the inner region of the Whirlpool galaxy show a regular spiral structure, but field lines in the molecular clouds decouple from those of the diffuse gas in the outskirts — closer to the companion galaxy Messier 51b. The field structure obtained with the far-infrared observations shows a strong distortion and large differences in their orientation with respect to the structure obtained with the radio observations. This decoupling might be related to the gravitational interaction with Messier 51b, but strikingly, this effect is not found in the inter-arm region where the gas density is much lower and many fewer stars are forming.

Earlier models of the global structure and evolution of spiral galaxies that ignored the effects of magnetic fields were based on the hypothesis that the diffuse and molecular gas shared a common magnetic structure. The most important result from this work is the proof that there is a new force contribution to be reckoned with — the kpc-scale magnetic field of the molecular clouds.

The shape of spiral galaxies results from the pattern of bright H II surrounding newborn stars. The magnetic field lines are also spiral shaped, but intriguingly, astronomers are not yet sure how either of these structures — the morphological or the magnetic — are formed or how they are connected. The morphological spiral arms are possibly the result of density waves that move around the disk, compressing the gas, and creating new stars as they pass. At the same time, these density waves might also compress the magnetic field lines, aligning the turbulent fields that form inside the molecular clouds.

The observed differences between both tracers of the magnetic field support the presence of small-scale magnetic dynamos. When combined with galactic rotation and shear forces, these dynamos would help to create the striking spiral patterns visible in the magnetic field structure of the Whirlpool galaxy. Moreover, the observed differences between the orientation of the pitch angle in the inter-arm and arm regions also support the presence of spiral density waves, which would be compressing the magnetic field lines as the morphological spiral arms move through the galaxy.

See the full article here .


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NASA/DLR SOFIA GREAT [German Receiver for Astronomy at Terahertz Frequencies]

NASA/DLR SOFIA High-resolution Airborne Wideband Camera-Plus HAWC+ Camera


SOFIA is a Boeing 747SP jetliner modified to carry a 106-inch diameter telescope. It is a joint project of NASA and the German Aerospace Center, DLR. NASA’s Ames Research Center in California’s Silicon Valley manages the SOFIA program, science and mission operations in cooperation with the Universities Space Research Association headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong Flight Research Center Hangar 703, in Palmdale, California.