Molecules could be broken and reborn in black hole splurges

The theory can explain why stars are created in the most extreme cosmic environments



A galaxy’s central supermassive black hole is an extremely powerful and energetic figure, with equally powerful outflow perpendicular to the galactic disk. Image credit: ESO/M. Kornmesser

Large amounts of molecules exist in the winds expelling from supermassive black holes at the centre of galaxies. This has perplexed astronomers since its discovery more than a decade ago, and has continuously questioned how molecules can survive in such a heated environment. New research from Northwestern University’s Centre for Interdisciplinary Research and Exploration in Astrophysics (CIERA) predict that these molecules are born in the winds, instead of simply surviving.

Astronomers use the detection of molecules to trace the coldest regions in space, and winds from black holes are normally thought to be highly energetic areas. Finding molecules in such outflows have been equated to discovering “ice in a furnace”. The work done by Lindheimer post-doctoral fellow Alexander Richings, and assistant professor at Northwestern University Claude-André Faucher-Giguère have theoretical shown that the winds provide a unique environment that could allow molecules to form and thrive.

Richings developed the computer code that modelled the chemical processes occurring in interstellar gas when heated by a supermassive black hole’s radiation. He explains, “When a black hole wind sweeps up gas from its host galaxy, the gas is heated to high temperatures, which destroy any existing molecules. By modelling the molecular chemistry in computer simulations of black hole winds, we found that this swept-up gas can subsequently cool and form new molecules.”

In 2015, the European Space Agency confirmed the existence of energetic outflows from supermassive black holes residing at the core of a galaxy. These outflows were thought to cast away any gas that could lead to star formation. They’re also thought to be the cause for the lack of star formation seen in elliptical galaxies. Then, in 2017, astronomers at the European Southern Observatory found that star formation could occur in such winds, which is highly contradictory to the previous findings. These findings have all come from extensive work using some of the world’s best telescopes, including the Herschel Space Observatory and the Atacama Large Millimetre/submillimetre Array.

The winds generated by supermassive black holes carry the gas necessary for initiate star formation. Image credit: ESA/ATG medialab

The new theory, proposed by Riching and Faucher-Gigère, states that molecules are being formed in the winds, leading to the additional star formation observed in such regions. While holding true to idea that black hole winds destroy molecules upon the initial clash, this new idea predicts that new molecules are created in the same domain, including hydrogen, carbon monoxide and water.

“This is the first time that the molecule formation process has been simulated in full detail, and in our view, it is a very compelling explanation for the observation that molecules are ubiquitous in supermassive black hole winds, which has been one of the major outstanding problems in the field,” says Faucher-Giguère.

Riching and Faucher-Giguère predict that such molecules will shine bright in infrared radiation, compared to pre-existing molecules. NASA’s James Webb Space Telescope will put this prediction under the spotlight when it is launched in spring 2019. If the theory proves true, the telescope will continue to map black hole outflows with its incredible infrared light gathering capabilities.

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