How 'Fat' Black Holes Grow Up: Virtual Observatory Reveals Mutual Galaxy Interaction

Supermassive black holes the size of more than one million solar masses exist at the center of most galaxies. Yet scientists have long wondered how these massive black holes get so "fat." Now, they may have found an explanation. It turns out that mutual interaction between galaxies could lead to the growth of these black holes.

Galaxy mergers frequently occur in regions where the density of galaxies is high. The collision and merger of galaxies change gas dynamics within them, and can trigger the gas infall to their central region. This may lead to the growth of the black hole.

In order to learn more about the growth of these black holes, the researchers turned to the "Virtual Observatory." This observatory is a system to make integrated use of various astronomical databases around the world via sharing over the Internet. The scientists collected the data on more than 10,000 active galactic nuclei (AGN) whose black hole mass had already been measured with spectroscopic observation with SDSS. Next, the researchers gathered data on galaxies surrounding active galaxies. Using the virtual observatory, the scientists could automatically extract only necessary galactic data from the large amount of data sets.

So what did they find? It turns out that the more massive black holes tend to be located in galactic environments with higher density. This connection between a massive black hole and the environment of its host galaxy is somewhat surprising; the radius of the overly dense region of galaxies is 100 million times larger than the radius of a massive black hole.

In fact, the researchers found another unexpected characteristic about these black holes. When it comes to black holes with a solar mass of 100 million or less, there is no correlation between the black-hole mass and the galaxy distribution. This suggests that there is a possibility that the growth process may be different between black holes above or below 100 million solar masses.

"A large part of the total picture, such as the formation mechanism of relatively small massive black holes, still remains unknown; one of the reasons is the lack of observation," said Yuji Shirasaki, one of the researchers, in a news release. "There are a lot of things to explore, including the mystery of how massive black holes are born."

The findings reveal a bit more about these black holes. Yet they also show the real potential of the virtual observatory. With the ability to process a huge amount of data in a short time, the observatory could pave the way for future discoveries.

The findings are published in The Astrophysical Journal.