omega Cen  


Spitzer infrared images of omega Centauri reveal where there is dust - and where there isn't

Omega Centauri is the largest globular cluster in our Galaxy, host to millions of stars. This makes it possible to catch stars in very brief, rare phases of their evolution, in particular during the final stages of their lives. It is then, as red giant stars, that we expect them to form dust grains, which play a vital role in the evolution of the Universe and the formation of rocky planets. Spitzer's unprecedented sensitivity allows us for the first time to detect this dust in small enough quantities to make up the balance for omega Centauri as a whole.

One of the nearest globular clusters, omega Centauri spans the size of the Full Moon on the sky. Spitzer's fine eye for detail shows many individual red giants even in the densest central parts of the cluster. It also shows many red galaxies at much greater distances, and the astronomers have had to be very careful to eliminate these and stars that do not belong to the cluster, from their analysis.

Stars in omega Centauri have very little of the building blocks for dust grains, and the Spitzer observations have made it crystal clear that dust in such stars only forms when they are at their most luminous. Even then, it seems to require strong pulsating movements of the stellar atmosphere for the material to be pushed out. The Spitzer images show no sign of dust in between the stars of the cluster, suggesting that it leaves the cluster to be mixed with other gas in the Galaxy. Some of the grains formed in this exotic place might one day enter our Solar system!"

Graduate students Martha Boyer (U. Minnesota) and Iain McDonald (U. Keele) did most of the work on the analysis and the publication of these data which feeds their theses. Jacco van Loon (U. Keele) is principal investigator of this programme. The team further includes Robert Gehrz, Charles Woodward (both U. Minnesota), Nye Evans (U. Keele), and Andrea Dupree (Harvard Smithsonian).

The observations were performed with the IRAC and MIPS infrared cameras onboard NASA's Spitzer Space Telescope, and have been published in the Astronomical Journal.