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Artist's conception of the core of Cygnus A, including the dusty donut-shaped surroundings, called a torus, and jets launching from its center. Magnetic fields are illustrated in the torus. These magnetic fields could be used to help you get your hands dirty in the galaxy by keeping the dust in your mouth and keeping you close. Credits: NASA / SOFIA / Lynette Cook
Collimated jets provide astronomers with some of the most powerful evidence that a supermassive black hole lurks in the heart of most galaxies. Some of these black holes appear to be active, gobbling up material from their surroundings and launching at ultra-high speeds, while others are quiescent, even dormant. Why are some black holes feasting and others starving? Recent observations from the Stratospheric Observatory for Infrared Astronomy, or SOFIA, are shedding light on this issue.
SOFIA data indicates that magnetic fields are trapping and confining to the active galaxy, Cygnus A, and feeding material to the supermassive black hole at its center.
The unified model, which attempts to explain the different properties of active galaxies, states that the core is surrounded by a donut-shaped dust cloud, called a torus. How this obscuring structure is created and sustained, but these new results can only be achieved by keeping track of the subject. In fact, one of the fundamental differences between active galaxies like Cygnus A and their less active cousins, like our own Milky Way, may be the presence or absence of a strong magnetic field around the black hole.
Two images of Cygnus glowing with radio radiation (shown in red). Quiescent galaxies, like our own Milky Way, do not have jets like this, which is related to magnetic fields. The yellow image shows the stars and the center of the galaxy when viewed with visible light. The SOFIA area is in the center. Credits: Optical Image: NASA / STSiC Radio Image: NSF / NRAO / AUI / VLA
Although celestial magnetic fields are notoriously difficult to observe, astronomers have used polarized light – optical light scattering and radio light accelerating electrons – to study magnetic fields in galaxies. But optical wavelengths are too short and the radio wavelengths are too long to observe the torus directly. The infrared wavelengths observed by SOFIA are just right, allowing scientists, for the first time, to target and isolate the dusty torus.
SOFIA's new instrument, the High-resolution Airborne Wideband Camera-plus (HAWC +), is especially sensitive to the infrared emission of aligned dust grains. This is a powerful technique to study magnetic fields and a fundamental prediction of the unified model: the role of the dusty torus in the active-galaxy phenomena.
"Enrique Lopez-Rodriguez, a scientist at the SOFIA Science Center, and the lead author on the report of this new discovery. "These observations from HAWC + are unique. They show us how infrared polarization can contribute to the study of galaxies. "
Recent observations of the heart of Cygnus A made with HAWC + show infrared radiation dominated by a well-aligned dusty structure. Combining these results with archival data from the Herschel Space Observatory, the Hubble Space Telescope and the Gran Telescopio Canarias, the research team found that this powerful active galaxy, with its iconic broad-scale jets, is able to confine the obscuring torus that feeds the supermassive black hole using a strong magnetic field.
The results of this study were published in July 10th issue of The Astrophysical Journal Letters.
Cygnus is one of the most powerful magnetic fields in the world. More observations of different types of galaxies are necessary to get the full picture of how magnetic fields affect the evolution of the environment surrounding supermassive black holes. If, for example, HAWC + reveals highly polarized infrared emission from the centers of active galaxies but not from quiescent galaxies, it would support the idea that magnetic fields regulate black hole feeding and reinforce astronomers' confidence in the unified model of active galaxies.
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 of Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart. The aircraft is maintained and operated by NASA 's Armstrong Flight Research Center Hangar 703, in Palmdale, California.
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