Academics and Research / Magazine Feature

DU astronomers shed new light on dying star

When DU astronomers Toshiya Ueta and Robert Stencel pointed the Spitzer Space Telescope at a dying star named R Hydrae in the constellation Hydra, they expected to see a spherical shell of low-temperature gas and dust ejected from the star by its stellar wind. Instead, they found a curved shell — called a bow shock wave — in front of the moving star, like the foamy breakers churned up in front of a ship under sail.

“This is sort of a surprising discovery,” says Ueta, who joined the DU faculty this fall.

Because space is cold and stars are hot, they actually evaporate, slowly losing mass. As a result, every star is surrounded by a bubble-like shock wave created by a stream of matter known as stellar wind.

Other stars with warped shock waves have been observed before, but never for this type of red giant star, known as an “asymptotic giant branch” star. Bow shock waves have been found with even larger, “supergiant” stars, Ueta notes.

Our sun’s heliosphere also is thought to be distorted in this way, with a shock wave that extends about twice the distance from the sun to Pluto. R Hydrae, while not unlike our sun, is much older. Understanding how it ejects gas and stardust at this stage of its evolution and how that material is reabsorbed into space could provide a glimpse of our own sun’s future, Ueta says.

As R Hydrae moves through space at approximately 50 kilometers per second, it discharges dust and gas into space. Because the star is relatively cool, that ejecta quickly assumes a solid state and collides with an “interstellar medium” made up mostly of widely scattered hydrogen molecules. The resulting dusty nebula is invisible to the naked eye but can be detected using an infrared telescope.

The distance from the star to the apex of the shock wave is approximately 400 times Pluto’s distance from the sun, and the scientists estimate that the matter contained in the bow shock nebula is equivalent to 400 Earths. Models created at the University of Manchester confirm that the bow shock is stable and predict that R Hydrae has been losing mass for at least 55,000 years.

“Our original intention was to detect and measure the density and distribution of material in the shell,” Ueta explains. “We have observed in total six objects, and this is just one of them. In the future, we will be observing hundreds more using the Japanese Akari infrared satellite successfully launched this February.”

The research was published in Astrophysical Journal Letters.

This article originally appeared in The Source, December 2006.

Comments are closed.