History of the Sun

Nebulous birth

The sky is no empty arena and stars are not the only actors. The other player in the cosmic drama is the cloud.

The business of the perfect interstellar cloud is to confiscate or at least filter the light of stars lying behind or even within it. Certain clouds referred to as bright nebulas are lit up from within. They are in the process of giving birth to a generation of stars, for like rats, cats and fish, stars are born in broods. Hence, the large, dusty and icy interstellar clouds are not only repositories for the ashes of defunct stars, but also for the material that will give body to new stars. Those stars currently forming, still buried deep within this cloudy placenta, can be observed in the radio, millimetre and infrared regions. Indeed, absorption by gas and dust is minimal at these wavelengths.

Still curled up at the heart of the parent cloud, the stellar embryos attract more matter in order to embark upon the visible phase of an object of fixed mass in hydrostatic equilibrium. They then disperse any surrounding matter and begin their own lives as free and independent stars.

In truth, star formation from molecular clouds is no easy subject to study. This is because the processes involved change the density from 10−23 g cm−3 to about 1 g cm−3 within a space of only a few tens of millions of years.