The Watery Birth of Stars

Logically, stars should not exist. They are born when clouds of interstellar gas collapse inwardly under their own weight, growing denser and hotter until nuclear fusion causes them to emit energy in the form of light. However, since heat forces matter to expand, this hot contracting gas could be expected to immediately move outward again, preventing star formation from ever reaching completion.

To resolve this paradox, scientists have postulated the existence of a water-based "cooling system" that regulates the temperature of interstellar clouds, enabling the contraction to continue. Now a Weizmann Institute study reported in Physical Review Letters provides experimental evidence that the billions of stars that populate our firmament indeed had a watery birth.

Researchers have theorized that water molecules in interstellar clouds exert a cooling effect by colliding with the gas particles and absorbing their energy that is later released in the form of radiation. But attempts to observe water in the stars using Earth-bound telescopes have always been thwarted by the presence of water particles in our planet's atmosphere. Scientists have, however, detected a similar substance that could be an intermediary product in water formation: hydronium, or H3O+, which contains three hydrogen atoms (as compared with water's two), along with one oxygen atom.

Drs. Daniel Zajfman and Oded Heber of the Weizmann Institute's Particle Physics Department have now completed an experiment demonstrating that water is indeed formed in interstellar clouds in a reaction involving hydronium. The experiment was carried out at an advanced installation called an ion storage ring at the University of Aarhus, Denmark, in collaboration with Aarhus researchers Dr. Lars Andersen, Dr. Dror Kella and Lisa Vejby- Christensen.

The scientists simulated the physical and chemical conditions in interstellar clouds and showed that water is formed there in a reaction between a charged hydronium molecule and a single electron. They also found that a permanent ratio between water and hydronium molecules is maintained in these clouds.

Special equipment aboard the U.S. research satellite SWAS, to be launched later this year, will be used to further explore the new findings without the interference of the Earth's atmosphere, in particular by directly measuring the quantity of water in the forming stars.

Dr. Zajfman holds the Martha S. Sagon Career Development Chair at the Weizmann Institute. Funding for the study was provided by the Israel Science Foundation and the Danish National Research Foundation.

The Weizmann Institute of Science is a major center of scientific research and graduate study located in Rehovot, Israel.