Opportunistic "Piranha" Black Holes Grow in Young Galaxies

New images from NASA's Chandra X-ray Observatory suggest that supermassive black holes grow faster in young galaxy clusters. These supermassive black holes grow so quickly that they can greatly influence the surrounding galaxies and clusters. The results of the study appeared in the July issue of The Astrophysical Journal Letters.

"The black holes in these early clusters are like piranha in a very well-fed aquarium," said Jason Eastman of Ohio State University (OSU) and first author of this study in a CXC press release. "It's not that they beat out each other for food, rather there was so much that all of the piranha were able to really thrive and grow quickly."

Using the Chandra X-ray Observatory, scientists looked at sample clusters and counted the galaxies that had growing supermassive black holes. Scientists, which call these black holes active galactic nuclei (or AGN), found that younger galaxies contained many more AGNs. Older galaxies, which are also closer to earth showed much fewer black holes.

A galaxy cluster is one of the largest structures known to scientists and is made up of groups of individual galaxies. Out of each galaxy, a few might have AGN. Younger galaxies appear to contain more gas that aids in both star formation and black hole growth. Scientists believe that this accounts for the growth of black holes in these areas.

Chandra was used by the researchers to find out the amount of black holes in four separate galaxy clusters. They compared galaxy clusters that were only 58 percent of the Universe's current age to those clusters that were 82 percent of the Universe's age.

The researchers found that the clusters that were further away, and therefore younger, had 20 times more supermassive black holes than a sample closer to our Universe.

"It's been predicted that there would be fast-track black holes in clusters, but we never had good evidence until now," said co-author Paul Martini, who also worked on the project in the CXC press release. "This can help solve a couple of mysteries about galaxy clusters."

One question that the scientists hope to answer is why so many younger blue, star-forming galaxies are present in younger clusters. Supermassive black holes are believed by scientists to destroy or expel cool gas through a series of eruptions. It is thought that this process might cause the gradual death of younger stars, leaving only the older, redder stars.

SOURCES:

"Chandra Catches "Piranha" Black Holes." CXC Release. URL: (http://www.chandra.harvard.edu/press/07_releases/press_072407.html)