The unexpected matter found in hostile black hole winds

New theory predicts origins of molecules in destructive cosmic outflows

The existence of large numbers of molecules in winds powered by supermassive black holes at the centers of galaxies has puzzled astronomers since they were discovered more than a decade ago. Molecules trace the coldest parts of space, and black holes are the most energetic phenomena in the universe, so finding molecules in black hole winds was like discovering ice in a furnace.

Astronomers questioned how anything could survive the heat of the energetic outflows, but a new theory from researchers in Northwestern University’s Center for Interdisciplinary Research and Exploration in Astrophysics (CIERA) predicts that these molecules are not survivors at all, but brand-new molecules, born in the winds with unique properties that enable them to adapt to and thrive in the hostile environment.

The theory, published in the Monthly Notices of the Royal Astronomical Society, is the work of Lindheimer post-doctoral fellow Alexander Richings, who developed the computer code that, for the first time, modeled the detailed chemical processes that occur in interstellar gas accelerated by radiation emitted during the growth of supermassive black holes. Claude-André Faucher-Giguère, who studies galaxy formation and evolution as an assistant professor in Northwestern’s Weinberg College of Arts and Sciences, is a co-author.

“When a black hole wind sweeps up gas from its host galaxy, the gas is heated to high temperatures, which destroy any existing molecules,” Richings said. “By modeling the molecular chemistry in computer simulations of black hole winds, we found that this swept-up gas can subsequently cool and form new molecules.

This theory answers questions raised by previous observations made with several cutting-edge astronomical observatories including the Herschel Space Observatory and the Atacama Large Millimeter Array, a powerful radio telescope located in Chile.


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