Omega Centauri tracking test

Omega Centauri is the most luminous globular cluster in our Galaxy. As the name indicates, it is located in the southern constellation Centaurus and is therefore observable only from the south.

The image shown here was obtained with the VLT on May 16, 1998, in red light (R band), i.e. while the mirror was still uncoated. It is a 10-minute exposure of the center of Omega Centauri and it demonstrates that the telescope is able to track continuously with a very high precision and thus is able to take full advantage of the frequent, very good atmospheric conditions at Paranal. The images of the stars are very sharp ( full-width-at-half-maximum (FWHM) = 0.43 arcsec) and are perfectly round, everywhere in the field. This indicates that the tracking was accurate to better than 0.001 arcsec/sec during this observation.

At a distance of about 17,000 light years, this cluster is barely visible to the naked eye as a very faint and small cloud. When Omega Centauri is observed through a telescope, even a small one, it looks like a huge swarm of numerous stars, bound together by their mutual gravitational attraction.

Most globular clusters in our Galaxy have masses of the order of 100,000 times that of the Sun. With a total mass equal to about 5 million solar masses, Omega Centauri is by far the most massive of its kind in our Galaxy.