Observations with Herschel-HIFI of water in a young Sun-like star reveal high-velocity "bullets" moving at more than 200,000 km/h from the star. This can be compared to the velocity of a bullet from an AK47 rifle, which is 2500 km/h or 80 times slower. It is a surprise that water molecules are observed at this high velocity – they should have been destroyed in the shock where temperatures exceed 100,000 degrees.

Therefore the observations reveal that water very likely reforms rapidly in the hot and dense shocked gas. The conditions are so favourable that approximately 100 million times the amount of water in the Amazone river is formed, every second! Furthermore, the observations make it possible to explore the most energetic phase of low-mass star formation, a phase that our own young Sun went through as it formed. Water is one of the molecules cooling the gas back down to low temperatures, allowing the young star to continue to grow.

HIFI
The source, L1448-MM, is located in the constellation Perseus at a distance of 750 light-years, The observations were made using the Herschel-HIFI instrument designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research. The data come from the Key Program "Water in Star Forming Regions with Herschel" (WISH) led by E.F. van Dishoeck. This study is led by L.E. Kristensen (Leiden Observatory) and is accepted for publication in Astronomy & Astrophysics.

See also Lars Kristensen explaining the water bullets on a short IAU film

The title of the publication is ‘Water in low-mass star-forming regions with Herschel (WISH-LM): High-velocity H2O bullets in L1448-MM observed with HIFI’.