black hole
Image: NASA/Penn State/F. BAUER et al.

Researchers using NASA's Chandra X-Ray Observatory to peer into the nearby Circinus galaxy (right) have found x-ray energies indicative of black holesincluding one with a mass some 50 times that of the sun. The new findings also reveal for the first time a black hole's periodic variability in x-rays outside the so-called Local Group of galaxies, which includes our own.

Astronomer Franz Bauer, a postdoctoral scholar at Pennsylvania State University, and his colleagues recognized the variable object by the characteristic shifts in the intensity of its emanating x-rays, which change according to a 7.5-hour cycle. This periodic variability, along with the brightness of the object, led the team to conclude that what they had detected was an x-ray binary systema normal star paired with a collapsed star (in this case, a supermassive black hole). "This is important because black holes with masses much larger than 10 times the mass of the sun, such as this one, are difficult to explain under current theories of star formation and destruction," Bauer explains. "Definitively finding a periodic signal in one allows us to test some of our past assumptions."

The findings also reveal that at least two different gas components exist near the nucleus of the galaxy. Furthermore, these gases have different distributions. "The Chandra observations of Circinus show us how complex the gaseous environment of supermassive black holes can be," notes Rita Sabruna of George Mason University. "Because it is close and thus easy to study," she adds, "Circinus provides an important testbed for what might be happening in other, more distant so-called active galaxies."