Dark Energy Camera Spies Cometary Globule Reaching for the Stars
The dark, dusty cometary globule known as CG 4 is spotlighted in this image from the Department of Energy-fabricated Dark Energy Camera mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF NOIRLab. How these hard-to-detect clouds get their distinctive structure is still unclear, but astronomers speculate that it’s a consequence of the hot, massive stars that surround them.
About 1300 light-years away, in the constellation Puppis, a ghostly hand appears to be emerging from the interstellar medium and reaching out into the cosmos. This cloudy, ominous structure is CG 4, a cometary globule that has been given the nickname ‘God’s Hand’. CG 4 is one of many cometary globules present within the Milky Way, and how these objects get their distinctive form is still a matter of debate among astronomers.
Cometary globules are a subclass of the dark nebulae known as Bok globules — isolated clouds of dense cosmic gas and dust surrounded by hot, ionized material. When these clouds exhibit stripping of material that results in an extended tail, they are referred to as cometary globules because of their vague resemblance to a comet, though they have nothing in common. The features that classify CG 4 as a cometary globule are hard to miss in this image captured with the Department of Energy-fabricated Dark Energy Camera (DECam) mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF NOIRLab. Its dusty head, which has a diameter of 1.5 light-years, and its long, faint tail, which is about eight light-years long, make CG 4 a comparatively small Bok globule, a general characteristic of cometary globules.
First recognized in 1976 from pictures taken with the UK Schmidt Telescope in Australia, cometary globules went undetected by astronomers for a long time because they are so faint. Their tails, shrouded in dark stellar dust, block most light from passing through. But with its special Hydrogen-alpha filter [1], DECam can pick up the faint red glow of ionized hydrogen present within CG 4’s head and around its outer rim. This light is produced when hydrogen becomes excited after being bombarded by radiation from nearby hot, massive stars.
The intense radiation generated by these neighboring massive stars, however, is gradually destroying the head of the globule and sweeping away the tiny particles that scatter the starlight. Still, the dusty cloud of CG 4 contains enough gas to feed the active formation of several new, Sun-sized stars.