Galaxy mergers trigger black hole growth

by | May 21, 2020 | Daily Space, Galaxies, Supermassive Black Holes | 0 comments

IMAGE: Pan-STARRS images of NGC 4088, NGC 0520, NGC 5218, NGC 4922 NED02, illustrating the different features used to classify galaxy mergers. CREDIT: A. Petric/B. Bays

Last summer, undergraduate Rebecca Minsley traveled to the University of Hawaii at Manoa’s Institute for Astrophysics to take part in a summer Research Experience for Undergraduates program. Commonly just called an REU, these internships are a right of passage for the majority of future researchers. I was an REU student at Kitt Peak’s National Radio Astronomy Observatory, and I have had my own summer students on related programs when I was at Harvard many years ago. 

Normally, students do their best on a 10-week project, and the expectation is that some small science will be completed that might lead to a publication or a software release. Well, for Rebecca Minsley, the science she worked on was less of an incremental improvement in understanding and more of a revolution in understanding. Her work, under mentor Dr. Andreea Petric, looked at myriad images of merging galaxies and sought to understand how supermassive black holes grow by looking at the gas dynamics. According to the press release, “Minsley studied the shapes of 630 galaxies using images from the Pan-STARRS survey. She classified the galaxies into mergers, early mergers, and non-mergers. And then compared the shapes to the light output of the same galaxies at longer mid-infrared wavelengths, where she could study the properties of the interstellar medium.” 

The result? They found that galaxy merger shocks heat gas in galaxies, and this heating prevents the formation of stars, allowing the gas to flow into the supermassive black hole, triggering black hole growth in step with the galaxies growing through the merger. This is the first step in developing the clean solution that astronomers have been looking for, but it is a first step that requires finding someone with 10 weeks to analyze 630 images, someone who was careful, smart, and cheaper than a Ph.D. This student fit the bill, and I can’t wait to see what she does in the future. 

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