'Chained' star-formation in the Trifid nebula
21 October 1998The bright massive central star in the spectacular Trifid nebula iscreating a second generation of young stars, in a 'chain reaction' processthat is taking place in less than a hundred thousand years. The occurrenceof such a process had been theoretically postulated, but now for the firsttime, the European Space Agency's ISO infrared space telescope is seeing itin unprecedented detail.
Stars form in nebulae by gravitational collapse of the dust and gas, and that is how the massive central star illuminating the Trifid nebula was born a hundred thousand years ago. But the energy that this star has been emitting during all this time has changed the physical and chemical conditions of its environment, accelerating the occurrence of another gravitational collapse which, as ISO sees now, is causing the secondary generation of stars to be born simultaneously in a short period of time. The process is called 'induced star-formation' and is indeed like a 'chain reaction' taking place in the nebula.
ISO is actually able to image several very young stars being born. They are as massive as 17 to 60 solar masses, well over the average for proto-stars (one to three solar masses); the astronomers, however, do not yet discard the possibility that each of these sources is a cluster with several components. The fact that these protostars are so massive indicates that they will evolve faster than usual, probably inducing more star-formation when they reach the adult stage.
"These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet," Cernicharo explains. "We also see all the clear signs of star formation, such as great condensations of very cold dust -at minus 250 degree Celsius- towards the proto-stars."
ISO observations were complemented by campaigns at non-infrared wavelengths with ground based telescopes, namely the Nordic Telescope at the Instituto de Astrofmsica de Canarias (Canary Islands, Spain), the 30 metres radiotelecope at IRAM in Granada (Spain) and the Very Large Array in Socorro (New Mexico, US).
Water refrigerates baby stars
Cernicharo and his group has been also very actively involved in the ISO discovery of water throughout the universe, a topic discussed today at the ISO meeting in Paris. The Spanish group presented their observations of the nebulae Orion and Saggitarius, where huge amounts of water vapour have been detected - "enough water as to fill the oceans of thousands of Earth-like planets," Cernicharo says.
This water was known to be absolutely necessary to cool the starforming nebula and thus allow the material to collapse and form new stars. But the amount of water now found by ISO is greater than expected, which gives new insights about chemical processes taking place in the nebulae. In the case of Orion, for instance, the interpretation of the new results requires a new model to be developed.