Integral sees the Galactic center playing hide and seek

Integral’s monitoring of the Galactic Center More Information ROLLOVER Credits: ESA/ISDC

The Galactic center is one of the most dynamic places in our Galaxy. It is thought to be home to a gigantic black hole, called Sagittarius A* (pronounced 'A star'). Since the beginning of the Integral mission, ESA's gamma ray observatory has allowed astronomers to keep watch on this ever-changing environment.

Integral has discovered many new sources of high-energy radiation near the galactic center. From February 2005, Integral began to regularly monitor the center of the Galaxy, and its immediate environment, known as the Galactic bulge.

Erik Kuulkers of ESA's Integral Science Operations Center, ESAC, Spain, leads the Galactic bulge monitoring program. Integral now keeps its high-tech eyes on about 80 high-energy sources in the galactic bulge. "Most of these are X-ray binaries," says Kuulkers.

Integral sees a ‘quiet’ Galactic Center More Information ROLLOVER Credits: ESA/ISDC

Integral’s average view of the Galactic Center More Information ROLLOVER Credits: ESA/ISDC

According to the Integral observations in April 2006, the high-energy rays from about ten sources closest to the galactic center all faded temporarily. Kuulkers excludes the possibility that a mysterious external force is acting on all the objects to drive them into quiescence. "All the sources are variable and it was just by accident or sheer luck that they had turned off during that observation," he says with a smile.

The fortuitous dimming allows astronomers to set new limits on how faint these X-ray binaries can become. It also allows a number of new investigations to be undertaken with the data.

"When these normally bright sources are faint, we can look for even fainter sources," says Kuulkers. These could be other X-ray binaries or the high-energy radiation from giant molecular clouds interacting with past supernovae. There is also the possibility of detecting the faint high-energy radiation from the massive black hole in our Galaxy's center.

Integral's Galactic bulge monitoring program will continue throughout this year. The data is made available, within a day or two of being collected, to the scientific community via the Internet from a dedicated web page at the Integral Science Data Center (IDSC), Geneva, Switzerland. This way, anyone interested in specific sources can watch for interesting changes and trigger follow up observations with other telescopes in good time.

Source / Credit: ESA