Astronomical Feature of the Month
Thackeray's Globules

   “Thackeray’s Globules” – strange name, interesting phenomena. What are they? Thackeray’s Globules are dark opaque dust clouds floating in space, they are seen by being silhouetted against nearby bright stars. Astronomer A.D. Thackeray first spied the globules in IC 2944 in 1950. Globules like these have been known since Dutch-American astronomer Bart Bok first drew attention to such objects in 1947. But astronomers still know very little about their origin and nature - except that they are generally associated with areas of star formation called “HII regions” due to the presence of hydrogen gas. The image above is a Hubble picture of IC 2944, a bright star-forming region in Centaurus, 5,900 light-years away. The largest of the globules in this image is actually two separate clouds that gently overlap along our line of sight. Each cloud is nearly 1.4 light-years along its longest dimension. Collectively, the clouds contain enough material to equal over 15 solar masses. Thanks to the remarkable resolution offered by the Hubble telescope, astronomers can for the first time study the intricate structure of these globules. The globules appear to be heavily fractured, as if major forces were tearing them apart. When radio astronomers observed the faint hiss of molecules within the globules, they realized that the globules are actually in constant, churning motion, moving supersonically among each other. This may be caused by the powerful ultraviolet radiation from the luminous, massive stars, which also heat up the gas in the region of glowing hydrogen gas, causing it to expand and stream against the globules, leading to their destruction. Despite their serene appearance, the globules may actually be likened to clumps of butter on a red-hot pan. It is likely that the globules are dense clumps of gas and dust that existed before the massive stars in the region were born. But once these luminous stars began to irradiate and destroy their surroundings, the clumps became visible when their less dense surroundings were eroded away, thus exposing them to the full brunt of the ultraviolet radiation and the expanding HII region. Had the appearance of the luminous O-stars been delayed a few hundred million years, it is likely that the globules would actually have collapsed to form several more low-mass stars like our Sun. Instead they are now being toasted and torn apart.

Io Volcano by Lionel Bret