When in the mid-1700s Abbé Nicholas Louis de la Caille discovered a colorful cluster of stars in the southern sky during a visit to South Africa, he pronounced it the "southern jewelbox."

The nickname stuck, but 250 years later a space-based telescope operated by the European Space Agency has produced an image of the jewelbox that the French astronomer could not have imagined.

"XMM-Newton gives us a much deeper view of NGC 2516 compared to previousobservations."

The recently launched XXM-Newton telescope is due to go into operational mode in June. Meanwhile, the southern jewelbox, also known as NGC 2516, was chosen as a calibration target because the locations of each of the stars in the cluster is already known with high precision.

The resulting X-ray image of the star cluster, which is 1,300 light-years away, is expected to help astronomers better understand so-called "open clusters."

Open star clusters are groups of stars formed together in the spiral arms of a galaxy and held together by mutual gravitational attraction. Usually irregular in shape, they can contain from a few dozen, to several hundred relatively young stars in an area up to 50 light-years across.

"XMM-Newton gives us a much deeper view of NGC 2516 compared to previous observations," said John Pye, a science project manager for the Earth-orbiting telescope. "We can better interpret the energies that have been detected, allowing us to determine the extreme temperatures of the star coronae. Such observations will help answer the question of whether all open clusters of the same age resemble each other or may have different aspects."