ESO: The dark Coalsack Nebula waits for new stars to light it up

ESO releases its latest astronomical findings:

A Cosmic Sackful of Black Coal

Dark smudges almost block out a rich star field in this new image captured by the Wide Field Imager camera, installed on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. The inky areas are small parts of a huge dark nebula known as the Coalsack, one of the most prominent objects of its kind visible to the unaided eye. Millions of years from now, chunks of the Coalsack will ignite, rather like its fossil fuel namesake, with the glow of many young stars.

This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope shows part of the huge cloud of dust and gas known as the Coalsack Nebula. The dust in this nebula absorbs and scatters the light from background stars.
This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope shows part of the huge cloud of dust and gas known as the Coalsack Nebula. The dust in this nebula absorbs and scatters the light from background stars. Larger image.

The Coalsack Nebula is located about 600 light-years away in the constellation of Crux (The Southern Cross). This huge, dusky object forms a conspicuous silhouette against the bright, starry band of the Milky Way and for this reason the nebula has been known to people in the southern hemisphere for as long as our species has existed.

The Spanish explorer Vicente Yáñez Pinzón first reported the existence of the Coalsack Nebula to Europe in 1499. The Coalsack 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. These two bright galaxies are clearly visible in the southern sky and came to the attention of Europeans during Ferdinand Magellan’s explorations in the 16th century. However, the Coalsack is not a galaxy. Like other dark nebulae, it is actually an interstellar cloud of dust so thick that it prevents most of the background starlight from reaching observers.

This zoom video starts with a broad view of the Milky Way. We then zoom in towards the famous small constellation of Crux, the Southern Cross, and to its left, the huge dark area called the Coalsack. The final sequence takes a very close look at some of the darkest parts of this cloud and also reveals many faint stars whose light has been reddened by scattering from the dust. Credit: ESO, N. Risinger (skysurvey.org), Digitized Sky Survey 2. Music: Johan Monell (www.johanmonell.com)

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 is, back in 1970, the Finnish astronomer Kalevi Mattila published a study estimating that the Coalsack has only about 10 percent of the brightness of the encompassing Milky Way. A little bit of background starlight, however, still manages to get through the Coalsack, as is evident in the new ESO image and in other observations made by modern telescopes.

This video takes a close-up look at a new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope. It shows part of the huge cloud of dust and gas known as the Coalsack Nebula, close to the Southern Cross in the southern Milky Way. The dust in this nebula absorbs and scatters the light from background stars, making many of them appear fainter and redder. Credit: ESO. Music: Johan Monell (www.johanmonell.com)

The little light that does make it through the nebula does not come out the other side unchanged. 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’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 Coalsack coalesces under the mutual attraction of gravity, stars will eventually light up, and the coal “nuggets” in the Coalsack will “combust”, almost as if touched by a flame.

This chart of the famous small constellation of Crux (The Southern Cross) shows all the stars that can be seen with the naked eye on a clear dark night. This constellation and its neighbours are also home to the huge dark nebula called the Coalsack, which can be easily seen without a telescope as a dark area superposed on the glow of the Milky Way. The location of a particularly dark part of this cloud, which has been imaged in detail using the Wide Field Imager on the MPG/ESO 2.2-metre telescope, is marked with a red circle.
This chart of the famous small constellation of Crux (The Southern Cross) shows all the stars that can be seen with the naked eye on a clear dark night. This constellation and its neighbours are also home to the huge dark nebula called the Coalsack, which can be easily seen without a telescope as a dark area superposed on the glow of the Milky Way. The location of a particularly dark part of this cloud, which has been imaged in detail using the Wide Field Imager on the MPG/ESO 2.2-metre telescope, is marked with a red circle. Larger image.

More information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

This rich landscape is part of the small constellation of Crux (The Southern Cross). The very bright star is Alpha Crucis, also know as Acrux, one of the four stars that make up the famous cross shape. Most of the upper left part of this image is filled with dark dusty clouds that form part of the huge dark nebula called the Coalsack.
This rich landscape is part of the small constellation of Crux (The Southern Cross). The very bright star is Alpha Crucis, also know as Acrux, one of the four stars that make up the famous cross shape. Most of the upper left part of this image is filled with dark dusty clouds that form part of the huge dark nebula called the Coalsack. Larger image.