Cooking habits of super-massive black holes could determine types of galaxies

The Supermanic Black Hole is in the heart of most galaxies, and a new study suggests that these hungry cosmic structures could ultimately define their hosts.

Using the Burst Alert Telescope (BAT) data on NASA's Swift satellite, an international team of scientists has discovered that galaxies of type I and type II are unusually different due to the speed at which their central black holes – also known as active galactic nuclei (AGJ) – perceives the surrounding matter, writes the statement of the University of Maryland.

Galaxy type I looks brighter when viewed from Earth. The new study denies a popular theory called a unified model, suggesting that the two types of galaxies look different because they are directed towards the Earth at different angles. By this model, type I galaxies are lighter because the II type galaxies are lined so that they are darkened with their own rings of dust.

"The unified model was the predominant wisdom for years. But this idea does not fully explain the differences we observe in the spectral signatures of the galaxy, and many have asked for an additional parameter to fill these gaps, "said Richard Mushotzky, a professor of astronomy at the University of Maryland and co-author of the study. "Our new data analysis of X-ray radiation from NASA's Burst Alert telescope suggests that I type galaxies are much more efficient in emitting energy."

The Burst Alerst telescope can detect high-energy or "hard" X-rays from the super-massive black hole in the center of the galaxy. Comparing X-rays, scientists have found that active galactic nuclei in Type I galaxies consume material and emit energy faster than they do in Type II galaxies, regardless of how the galaxy is directed towards the Earth, according to the study.

"Our results suggest that this is related to the amount of dust near the central black holes," Mushotzky said in a statement. "Type II galaxies have much more dust near the black holes, and this dust crashes with gas as it enters the black hole."

In addition to data from Swift satellite, scientists have also measured the mass and rate of growth of active galactic nuclei in type I and type II galaxies, using data from 12 different Earth telescopes

Previous studies mostly focused on type II galaxies because the active galactic nuclei in type I galaxies are very bright and therefore harder to study. By a unified model, this is not a problem because it is believed that all active galaxies are basically the same.

However, a new study reveals that more attention needs to be paid to the type I galaxies.

"Now, because our results suggest that the two types of galaxies are fundamentally different, it is likely that many scientists will reevaluate their data and reconsider the type I galaxies," Mushotzky said. "By putting us in the way of a better understanding of the differences between galaxies hosted by active type I and type II nuclei, this paper will help us understand how superhuman black holes affect the evolution of their host galaxies."

Their findings were published on September 28 in the journal Nature.

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