Stellar reservoir

Molecular cloud on the verge of star formation.-

THE European Space Agencys Herschel space observatory has discovered enough water vapour to fill the earths oceans more than 2,000 times over in a gas-and-dust cloud that is on the verge of collapsing into a new sun-like star. Water, essential to life on the earth, has previously been detected outside of the solar system as ice coated onto tiny dust grains near sites of active star formation and in proto-planetary discs capable of forming alien planetary systems. The new observations of a cold pre-stellar core, known as Lynds 1544, in the constellation of Taurus are the first detection of water vapour in a molecular cloud on the verge of star formation. The water vapour, it is believed, has been liberated from icy dust grains by high-energy cosmic rays passing through the cloud. L1544 was studied as part of the Water in star-forming regions with Herschel (WISH) programme. The work has been published in Astrophysical Journal Letters.

To produce that amount of vapour, there must be a lot of water ice in the cloud, more than three million frozen earth oceans worth, says Paola Casella, one of the authors from the University of Leeds. The understanding was that all the water was frozen onto dust grains. Now we will need to review our understanding of the chemical processes, in particular, the importance of cosmic rays to maintain some amount of water vapour.

The observations have also revealed that the water molecules are flowing towards the heart of the cloud where a new star will probably form, indicating that gravitational collapse of the whole cloud towards the centre has just started. Some of the water vapour detected in L1544 will go into forming the star, but the rest will be incorporated into the surrounding disc, providing a rich water reservoir to feed potential new planets.