CAPTION: This Hubble Space Telescope image of the narrow-line Seyfert 1 galaxy
MCG 6-26-12 shows a bright star-like nucleus indicative of a supermassive black
hole and a stellar bar that extends from the nucleus to spiral structure in the
outer regions of the galaxy. This galaxy is at a redshift of 0.032, which
places it at a distance from the Earth of 150 million parsecs (480 million
light years). The image was presented to the American Astronomical Society
meeting in Nashville, Tennessee on May 26, 2003. Positive and negative
reproductions are shown.
PHOTO CREDIT: Michael Crenshaw (Georgia State University)
PRESS RELEASE, May 2003
FOR RELEASE: 10:00 a.m. CDT, May 26, 2003
GALACTIC BARS FEED SUPERMASSIVE BLACK HOLES
CONTACTS:
Dr. D. Michael Crenshaw
Professor of Physics and Astronomy
Georgia State University
Atlanta, GA 30303
Phone: 404-651-1365
Email: crenshaw@chara.gsu.edu
Dr. Steven B. Kraemer
Professor of Physics
The Catholic University of America
Washington, DC 20064
Phone: 202-319-4335
Email: stiskraemer@yancey.gsfc.nasa.gov
Astronomers have discovered that supermassive black holes in the centers of some galaxies are accreting matter at fantastic rates with the assistance of galactic bars. Using images from the Hubble Space Telescope, Dr. Michael Crenshaw of Georgia State University and Drs. Steve Kraemer and Jack Gabel of The Catholic University of America found that galaxies with the most energetic black holes tend to have large stellar bars. The bars are apparently funneling gas and dust from the outer to the inner regions of the galaxies to provide ample supplies of "food" to the black holes. This finding is important for understanding the connection between the activity level of supermassive black holes and the properties of their host galaxies. The results of this study are being presented today to the American Astronomical Society meeting in Nashville, Tennessee.
Observations over the past decade have revealed that the core of every bright galaxy likely harbors a supermassive black hole with a mass of a million to a billion times that of the Sun. Nearly all of these black holes, including the one in the nucleus of our own Milky Way galaxy, are currently inactive. However, about one percent of the supermassive black holes in the present-day Universe are actively accreting large amounts of matter, and each is emitting copious amounts of radiation from a hot accretion disk surrounding it. Brilliant emission from a tiny region in the nucleus of a galaxy is the signpost of an active black hole.
Now astronomers have found a direct link between the most energetic and therefore most rapidly accreting black holes and their host galaxies. The new results are based on images of Seyfert 1 galaxies (named after their discoverer), which are almost always spiral galaxies with bright stars arranged in spiral arms, and which have bright nuclei indicating active black holes. Unlike previous studies, this one focused on a particular subclass called narrow-line Seyfert 1 galaxies, so named because the emission lines from hot gas in their nuclei are spread over a relatively narrow range in velocity. According to Dr. Crenshaw, "narrow-line Seyfert 1 galaxies are interesting because their black-hole masses are only about a million times that of the Sun, but they are accreting matter at the highest possible rate for their masses, about one solar mass per year. They could be likened to rambunctious juveniles that are eating rapidly on their way to becoming more massive and less active adults."
As with normal spiral galaxies, about one-third of Seyfert 1 galaxies have a bar made up of stars that extends from close to the nucleus to the spiral structure in the outer regions of these galaxies. However, the astronomers noticed that 65% of the narrow-line Seyfert 1 galaxies have bars, whereas only 25% of the normal Seyfert 1 galaxies have bars. Furthermore, the four narrow-line Seyfert 1 galaxies in the sample that are thought to be the most active all have bars. According to Dr. Kraemer, "stellar bars provide a very efficient means for driving gas and dust from the outer regions of the galaxy into the nucleus, so it is not too surprising that the most active black holes are in galaxies with bars."
However, the mysteries of black hole feeding are far from being solved. Most of the stellar bars do not extend all the way down to the nucleus, but instead terminate at about 1000 parsecs (3300 light years) from the supermassive black hole. A number of recent studies have shown that there are inner spirals and in a few cases bars of dusty gas that may represent pathways to the black hole's accretion disk. However, many normal galaxies with inactive black holes also have inner dusty spirals and bars, so it is not clear exactly what mechanisms control the activation and subsequent feeding of a supermassive black hole. Deeper images of a larger sample of Seyfert 1 galaxies in different colors with the Hubble Space Telescope may help to clear up these mysteries.
This work was supported by NASA, Georgia State University, and The Catholic University of America. The images for this research were obtained from the Multimission Archive at the Space Telescope Science Institute.