When dwarves explode, they do so with the help of giants – at least when the dwarves and giants are stars. Exploding white dwarf stars leave behind a rapidly expanding cloud of “stardust” known as a Type Ia supernova. These events, which shine billions of times brighter than our sun, are all presumed to be extremely similar and thus have been used extensively as cosmological reference beacons to trace distance and the evolution of the universe.
Astronomers have now – for the first time ever – provided a unique set of observations, enabling them to find traces of the material that had surrounded a white dwarf star before it exploded. No Type Ia supernova event has ever before been observed at this level of detail over a several-month-long period following the explosion.
These results were recently published in the journal Science. The data were collected from the ESO Very Large Telescope in Chile and the 10-meter Keck telescope in Hawaii by two teams of researchers: The one at ESO was headed by Dr. Ferdinando Patat, and the Keck team, based at the California Institute of Technology, USA, was led by Dr. Avishay Gal-Yam. Gal-Yam recently joined the Weizmann Institute’s Condensed Matter Physics Department.
The data the scientists collected provided evidence to support a widely accepted model for Type Ia supernovae, one in which a white dwarf star interacts with a companion star – a red giant. The white dwarf is small but extremely dense; and because of its strong gravitational pull, it continually feeds on gases from its giant companion. When the mass of the white dwarf grows past a critical value, it explodes.
Combining their observations, which took place over the course of four months, with archival data, the astronomers detected the presence of a number of expanding shells surrounding a Type Ia supernova event. The makeup of these shells suggests they are the remnants of the red giant star that fed the white dwarf.
Dr. Avishay Gal-Yam’s research is supported by the Nella and Leon Benoziyo Center for Astrophysics.
Physicist to the Stars
Dr. Avishay Gal-Yam was born in Jerusalem and, after serving as an officer in the IDF, received his Ph.D. in physics and astronomy from Tel Aviv University. From Tel Aviv, he moved to California to conduct postgraduate research at the California Institute of Technology (Caltech). He was drawn to astrophysics, he says, because “many of the fundamental parameters of physics can be measured through astrophysical studies. Astrophysics is a window on the makeup of the universe.”
Beginning with his Ph.D. research, Gal-Yam has searched for supernovae in massive galaxy clusters. His calculations of the lifespan of these stars – from their formation to the final, brilliant explosion – have provided evidence as to the type of star system that ends its days as a supernova. While at Caltech, Gal-Yam assembled a large group of scientists to observe fifty instances of so-called core-collapse supernovae, and the scientists are now using these data to understand the physical processes involved in core collapse.
Gal-Yam joined the Weizmann Institute in 2007. He is married and the father of three children. He enjoys playing sports, and he and his family like to travel and hike together.