All quiet in the nursery?

The dark patch snaking across this spectacular image of a field of stars in the constellation of Ophiuchus (The Serpent-bearer) is not quite what it appears to be.

Although it looks as if there are no stars here, they are hidden behind this dense cloud of dust that blocks out their light. This particular dark cloud is known as LDN 1768.

Despite their rather dull appearance, dark nebulae like LDN 1768 are of huge interest to astronomers, as it is here that new stars form. Inside these vast stellar nurseries there are protostars — stars at the earliest stage of their lives, still coalescing out of the gas and dust in the cloud.

Protostars are relatively cold and have not yet begun to produce enough energy to emit visible light. Instead, they emit radiation at submillimetre wavelengths, which human eyes cannot see. Luckily, unlike visible light, light at submillimetre wavelengths is not absorbed by the surrounding dust. By using special telescopes that are sensitive to submillimetre radiation, like the Atacama Large Millimeter/submillimeter Array (ALMA) observatory, we can see through the dust and find out more about the protostars within the cloud.

Eventually, the protostars will become dense and hot enough to start the nuclear reactions that will produce visible light and they will start to shine. When this happens, they will blow away the cocoon of dust surrounding them and cause any remaining gas to emit light as well, creating the spectacular light show known as an HII region.