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Weinberg researchers discover that cold molecules form in black hole winds

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Technological Institute. Postdoctoral fellow Alexander Richings and Weinberg Prof. Claude-André Faucher-Giguère, whose offices are in Tech, developed a theory that may explain why “cold” molecules can be found in the very energetic winds blowing from black holes.

Technological Institute. Postdoctoral fellow Alexander Richings and Weinberg Prof. Claude-André Faucher-Giguère, whose offices are in Tech, developed a theory that may explain why “cold” molecules can be found in the very energetic winds blowing from black holes.

Daily file photo by Colin Boyle

Daily file photo by Colin Boyle

Technological Institute. Postdoctoral fellow Alexander Richings and Weinberg Prof. Claude-André Faucher-Giguère, whose offices are in Tech, developed a theory that may explain why “cold” molecules can be found in the very energetic winds blowing from black holes.

Alane Lim, Reporter

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Weinberg researchers have developed a theory that may explain why “cold” molecules can be found in the very energetic winds blowing from black holes.

According to a Jan. 30 news release, postdoctoral fellow Alexander Richings and physics and astronomy Prof. Claude-André Faucher-Giguère created a computer code that modeled the chemical processes found in the winds driven by supermassive black holes at the centers of some galaxies, and discovered that new molecules form within the winds.

In November, the study was published in Monthly Notices of the Royal Astronomical Society.

Richings said previous work had indicated that the winds “swept” out existing molecules from a galaxy. The winds from these supermassive black holes can drive gas out of a galaxy at very high speeds, he added.

“Gas in the galaxy is what forms the stars we see. … It’s like the fuel for star formation,” Richings said. “When we have (these) supermassive black holes drive the gas out of the galaxy, it’s thought it can end star formation.”

Faucher-Giguère added that because supermassive black holes are the most energetic objects in the universe, the winds are expected to be very hot. However, astronomers detected these winds around the year 2010 and found they emitted cold molecular gas, he added.

The team’s simulations show how this cold gas can form, Faucher-Giguère said.

“These were really the first numerical simulations that included all the equations that are necessary to capture how molecules are formed and destroyed in interstellar gas,” Faucher-Giguère said.

Postdoctoral fellow Jonathan Stern, who works in Faucher-Giguère’s group but has not worked on the project, said Richings’ work yielded predictions that can be easily tested against observations.

Richings said the team’s work looked at molecules like molecular hydrogen and carbon monoxide. The authors could compare the simulated molecules to those seen in space, he added.

The code modeled the process over one million years, which is the typical timescale of the outflows that have been observed, Richings said. He added that the simulations were run on several supercomputers, which have a higher computational ability than most computers, including one at Northwestern.

Faucher-Giguère said these new molecules were somewhat warmer than most molecules familiar to astronomers — over one thousand degrees Kelvin compared to tens or hundreds of degrees — so they should be brighter in infrared radiation.

Sometime next year, NASA is launching a telescope that is sensitive to infrared radiation, Faucher-Giguère said, adding that this new instrument should be able to map these “molecular outflows” in a large number of galaxies if the team’s theory is correct.

Stern said work like Richings’ matters because it helps scientists understand how the universe evolved.

“We think that this interaction between black holes and galaxies has a major effect on the development of the universe — the development of how stars are built up, how galaxies are formed,” he said. “By doing these kinds of studies, we can actually understand (the) history of the universe.”

Email: alane.lim@u.northwestern.edu
Twitter: @thisisalane

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