This image from the Wide Field Imager, a camera installed on the MPG/ESO 2.2-m telescope at ESO’s La Silla Observatory in Chile, shows part of the huge dark cloud of gas and dust known as the Coalsack Nebula.
This image shows part of the Coalsack Nebula, an opaque interstellar dust cloud that obscures the light of the background Milky Way stars; dust grains in the cloud redden the starlight that reaches us by absorbing blue light preferentially. Image credit: ESO.
The Coalsack Nebula, also known as TGU H1867, is located approximately 600 light-years away in the southern part of the constellation Crux, and is 20 – 30 light-years across.
It is the most prominent and conspicuous dark nebula in the skies, well visible to the naked eye as big dark patch in the Milky Way.
The nebula was pre-historically known to the people of the Southern Hemisphere. The Incas tell that the god Ataguchu, in a fit of temper, kicked the Milky Way and a fragment flew off, forming the Small Magellanic Cloud where it landed on the sky, and leaving the black mark of the Coalsack behind.
The first European to see this remarkable object was probably the Spanish navigator and explorer Vincente Yanez Pinzon when he sailed to the South American coast in 1499. Amerigo Vespucci named it ‘il Canopo fosco’ in about 1503-1504.
The Coalsack Nebula later garnered the nickname of the Black Magellanic Cloud, a play on its dark appearance compared to the bright glow of the two Magellanic Clouds, which are in fact satellite galaxies of the Milky Way.
The first formal description was given by the Italian-born historian Peter Martyr d’Anghiera between 1511 and 1521.
Later, the French astronomer and priest Nicholas Louis de Lacaille described this southern object in an appendix to his 1755 catalog.
Like other dark nebulae, the Coalsack Nebula is actually an interstellar cloud of gas and dust so thick that it prevents most of the background starlight from reaching observers.
A significant number of the dust particles in dark nebulae have coats of frozen water, nitrogen, carbon monoxide and other simple organic molecules. The resulting grains largely prevent visible light from passing through the cosmic cloud.
To get a sense of how truly dark the Coalsack Nebula is, back in 1970, the Finnish astronomer Kalevi Mattila published a study estimating that the nebula has only about 10% of the brightness of the encompassing Milky Way.
A little bit of background starlight, however, still manages to get through the cloud, as is evident in the new ESO image.
The light we see in this image looks redder than it ordinarily would. This is because the dust in dark nebulae absorbs and scatters blue light from stars more than red light, tinting the stars several shades more crimson than they would otherwise be.
Millions of years in the future the Coalsack Nebula’s dark days will come to an end. Thick interstellar clouds like the Coalsack contain lots of dust and gas – the fuel for new stars.
As the stray material in the nebula coalesces under the mutual attraction of gravity, stars will eventually light up, and the coal ‘nuggets’ in it will ‘combust.’
