Shrinking Giants, Exploding Dwarves

New, detailed observations of a supernova show evidence that a white dwarf star "fed" off a red giant to gain the critical mass needed for explosion.

When white dwarf stars explode, they leave behind a rapidly expanding cloud of 'stardust' known as a Type Ia supernova. These exploding 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 obtained with the ESO Very Large Telescope in Chile and the 10-meter Keck telescope in Hawaii, enabling them to find traces of the material that had surrounded a white dwarf star before it exploded. Their data set is unique in that no Type Ia supernova event has ever been observed at this level of detail over a several-month period following the explosion.

These observations support a widely accepted model proposing that a white dwarf star interacts with a companion star – a red giant. Due to the white dwarf’s strong gravitational pull, this companion star continuously loses mass through ‘force feeding’ its gases to the white dwarf. When the mass of the white dwarf grows past a critical value, it explodes.

Through their observations, which took place over the course of four months, and combined with archival data, the astronomers detected the presence of a number of expanding shells surrounding a Type Ia super-nova event. The make-up of these shells suggests they are the remnants of the red giant star that fed the white dwarf.

These results were recently published in the journal Science. The data were collected by two teams of researchers; one at ESO headed by Dr. Ferdinando Patat, and one at the California Institute of Technology, USA, led by Dr. Avishay Gal-Yam. Dr. Gal-Yam has recently joined the Weizmann Institute of Science as a senior scientist in the Condensed Matter Physics Department.

Dr. Avishai Gal-Yam's research is supported by the Nella and Leon Benoziyo Center for Astrophysics.

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