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Starrfield adds stellar expertise to study of ‘Star Wars’ explosions


January 24, 2007

An international team of astronomers (including one from ASU) are using the Hubble Space Telescope to obtain the first direct optical images of the aftermath of a titanic explosion that occurred recently in a star system 5,000 light-years from Earth.

Speaking at the American Astronomical Society’s meeting in Seattle, the team’s members – including ASU Regents’ Professor Sumner Starrfield – said their work helps shed light on the peculiar behavior of a star system called RS Oph located in the constellation of Ophiuchus.

RS Oph consists of a “white dwarf,” a super-dense dead star about the size of the Earth, in close orbit around a much larger “red giant” star. The two stars are so close together that hydrogen-rich gas from the outer layers of the red giant is continuously pulled onto the white dwarf by its high gravity.

Enough gas has been accreted that a runaway thermonuclear explosion occurs on the white dwarf’s surface. In less than a day, RS Oph’s energy output increased to more than 100,000 times that of the Sun, and accreted gas with about the mass of Earth is ejected into space at speeds of several million miles per hour.

Explosions such as this occurring again and again on time scales of decades can only be explained if the white dwarf is near the maximum mass it could have without collapsing to become an even denser object – a neutron star – and thus ending its days in a supernova explosion. What also is unusual in RS Oph is that the red giant is losing enormous amounts of gas in a wind that envelops the whole system. As a result, the explosion on the white dwarf occurs “inside” its companion’s extended atmosphere, and the ejected gas then slams into it at very high speed.

“The Hubble observations clearly resolve the effects of high-velocity material that has been explosively ejected from the white dwarf affecting the environment of the companion star – it is ‘Star Wars’ in action,” Starrfield says.

The work has important implications for understanding the environment into which the explosion occurred and the evolution of stars that will eventually explode as supernovae, Starrfield adds.

Other members of the team are: Michael Bode, Dan Harman and Matt Darnley of Liverpool John Moores University, UK; Tim O’Brien of the Jodrell Bank Observatory at University of Manchester, UK; Howard Bond of the Space Telescope Science Institute, Baltimore; Nye Evans of University of Keele, UK; Stewart Eyres of University of Central Lancashire, UK; and Michael Shara of the American Museum of Natural History, New York.