In space, dense clouds of cosmic gas and dust are the birthplaces of new stars. In visible light, this dust is often dark and obscuring, concealing the stars behind it.
Indeed, when astronomer William Herschel observed one such cloud in the constellation of Scorpius way back in 1774, he thought it was a region empty of stars and is said to have exclaimed, "Truly there is a hole in the sky here!"
To further their improvement of star formation, astronomers require telescopes capable of observing stellar phenomenon at longer wavelengths, such as the submillimetre range, in which the dark dust grains shine rather than absorb light.
APEX, located on the Chajnantor Plateau in the Chilean Andes, is the largest single-dish submillimetre-wavelength telescope operating in the southern hemisphere, and is considered an ideal destination for astronomers studying the birth of stars.
Located in the constellation of Orion (The Hunter), approximately 1500 light-years away from Earth, the Orion Molecular Cloud Complex is the closest region of massive star formation to our planet, and is home to a treasury of bright nebulae, dark clouds and young stars.
The image above shows just part of this vast complex in visible light, with the APEX observations overlaid in brilliant orange tones that seem to set the dark clouds on fire. Often, the glowing knots from APEX correspond to darker patches in visible light - the sign of a dense cloud of dust that absorbs visible light, but glows at submillimetre wavelengths, and possibly a site of star formation.
The bright patch below of the center of the image is the nebula NGC 1999. This region - when seen in visible light - is what astronomers refer to as a reflection nebula, where the pale blue glow of background starlight is reflected from clouds of dust.
The nebula is primarily illuminated by the energetic radiation from the young star V380 Orionis lurking at its heart. In the center of the nebula is a dark patch, which can be seen even more clearly in a well-known image from NASA's Hubble Space Telescope.
"Normally, a dark patch such as this would indicate a dense cloud of cosmic dust, obscuring the stars and nebula behind it. However, in this image we can see that the patch remains strikingly dark, even when the APEX observations are included," an ESO (European Organisation for Astronomical Research) rep explained.
"Thanks to these APEX observations, combined with infrared observations from other telescopes, astronomers believe that the patch is in fact a hole or cavity in the nebula, excavated by material flowing out of the star V380 Orionis. For once, it truly is a hole in the sky!"