NASA Completes Survey of Nearby Supermassive Black Holes
Shown here are higher-energy X-ray objects in or near our galaxy. The sources are largely stellar-mass black holes, neutron stars, pulsars and supernova remnants. The colors depict X-ray energy in which red is lower energy and blue is the highest; white is an even mix of lower-energy and higher-energy X-ray photons. These sources are not included in the Swift survey because they are too distant for the satellite to image.
Credit: NASA/Swift/BAT/Markwardt et al.

A new census compiled by astronomers contains the location of every local galaxy with a supermassive black hole at its center.

"We are confident we are seeing every, active supermassive black hole within 400-million-light-years of Earth," said Jack Tueller of NASA Goddard Space Flight Center in Maryland who led the census effort.

Called active galactic nuclei, or AGN, these black holes have masses of up to billions of Suns compressed into a region about the size of our solar system. The all-sky census [image], performed using NASA's Swift satellite over a nine-month period, detected more than 200 nearby AGN.

Supermassive black holes are thought to lie at the hearts of nearly every massive galaxy, but only a few percent appear to be active. The black holes of some galaxies, like our Milky Way, were likely once active but are now dormant for reasons that are still unclear. One idea is that they've simply consumed all the material in their immediate vicinities. Such dormant supermassive black holes were not counted in the survey.

Among the key findings from the survey [image] was the detection of AGN in so-called "starbursts" galaxies with intense star forming activity. These discoveries will enable scientists to test a theory called "co-evolution," which states that black hole activity and star formation go hand in hand, the researchers say.

The findings were presented at a press conference today at the meeting of the American Astronomical Society's High Energy Astrophysics Division in San Francisco.