Black Hole’s “Burp” Might Help In Forming New Stars

The black hole's 'burp' is seen here. NASA/CXC/Univ of Texas/STScI/E.Schlegel et al

Black holes are thought to be world destroyers, but some new evidence suggests that in some cases, they can actually help in the formation of stars.

In the findings, made by the Chandra X-ray Observatory and presented yesterday at the 227th Meeting of the American Astronomical Society, researchers highlighted the dramatic feedback mechanisms between a galaxy and its supermassive black hole. This black hole has been observed producing outbursts of material, which are compressing gas, and astronomers believe it will induce new star formation.

The galaxy, called M51b, is the small companion of the more famous Whirlpool galaxy. It’s a small elliptical galaxy that is slowly being assimilated by its larger spiral companion. When galaxies merge, the strong forces produce intense episodes of star formation and as the gas moves around, the supermassive black holes at their center wake up and start gorging on whatever is around them.

The more material around a black hole, the more energy the black hole releases. This energy creates galactic winds that then snuff out potential new stars. This feedback between galaxies, stars, and black holes regulates how a galaxy evolves during a merger.

"We think that feedback keeps galaxies from becoming too large," said Marie Machacek, a coauthor of the study from the Harvard-Smithsonian Center for Astrophysics (CfA), in a statement. "But at the same time, it can be responsible for how some stars form. This shows that black holes can create, not just destroy."

The team has detected two enormous arcs of material glowing in X-rays, which were emitted by the black holes several million years ago. Observing the region outside the arcs, they saw cool hydrogen, which is the necessary component for stars to form. The arcs have been plowing material from the center of the galaxy to the outskirts, and now the material is dense enough and cool enough to trigger star formation.


M51b, seen top left, is a companion of the larger Whirlpool Galaxy. NASA/CXC/Univ of Texas/STScI/E.Schlegel et al

Due to their position in the galaxy, the researchers think this is a rare view of the intermediate stage of the feedback process.

"For an analogy, astronomers often refer to black holes as 'eating' stars and gas. Apparently, black holes can also burp after their meal," said Eric Schlegel of The University of Texas in San Antonio, who led the study.

"Our observation is important because this behavior would likely happen very often in the early universe, altering the evolution of galaxies. It is common for big black holes to expel gas outward, but rare to have such a close, resolved view of these events."

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