University of Denver News Releases
Friday, December 1, 2006
University of Denver astronomers shed new light on dying star
NASA’s Spitzer Space Telescope reveals R Hydrae’s bow shock wave
When University of Denver astronomers Toshiya Ueta and Robert Stencel pointed NASA’s Spitzer Space Telescope at a dying star named R Hydrae (R Hya) 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. 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. Warped shock waves have been observed before with stars other than R Hya, 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 Hya, 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 Hya 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 R Hya’s shock wave is approximately 400 times Pluto’s distance from the sun, and 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 Hya 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 to infer how the star lost mass in the past,” 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 the Sept. 1 issue of Astrophysical Journal Letters. Scientists collaborating in the study are:
T. Ueta (University of Denver)
A. K. Speck (University of Missouri-Columbia, PI)
R. E. Stencel (University of Denver)
F. Herwig (Los Alamos National Lab)
R. D. Gehrz (University of Minnesota)
R. Szczerba (N. Copernicus Astronomical Center, Poland)
H. Izumiura (Okayama Astronomical Observatory, Japan)
A. A. Zijlstra (University of Manchester)
W. B. Latter (NASA Herschel Science Center)
M. Matsuura (National Astronomical Observatory, Japan)
M. Meixner (Space Telescope Science Institute)
M. Steffen (Astrophysics Institute Potsdam, Germany)
M. Elitzur (University of Kentucky)
Also with
C. J. Wareing (University of Manchester)
T. J. O’Brien (University of Manchester)
The University of Denver (www.du.edu), the oldest private university in the Rocky Mountain region, enrolls approximately 10,850 students in its undergraduate and graduate programs. The Carnegie Foundation classifies the University of Denver as a Doctoral/Research University-Extensive.
Total undergraduate enrollment for fall 2006 is 5,149, including 1,142 first-time, first-year, first-time students, compared to 1,097 last year. Graduate enrollment is 5,701.
NASA’s Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.
Editors Note: Images of R Hydrae, an artist’s conception of the bow shock wave and additional scientific information about the object may be obtained at the following website: http://sscws1.ipac.caltech.edu/Imagegallery/image.php?image_name=sig06-029.