The future demise of our Sun is being played out 550 light years away by a star in the constellation Cygnus, the Swan, as a death scene that is drawn-out but spectacular. Chi Cygnus, a red giant much like the one our Sun will become, sits in the neck of the Swan and seems to throb as it expires, as if with a cosmic pulse. New images of the surface of the star captured the details of these death throes in beautiful relief and may change the understanding of how stars like ours end their lives.
Chi Cygnus is a so-called Mira variable, named for Mira, the first star recognized to periodically vary in brightness by David Fabrius in 1596. The pulsing reflects the rhythmic trapping and release of heat from a deep layer of gas around the star. As the star uses the dregs of its hydrogen fuel, it alternately coughs and roars to life like a car running on fumes. To our distant eyes and instruments this looks like a dimming as the star pushes away its puffy outer layers and an intense brightening as the star contracts. The whole cycle takes about 408 days. If it were placed in our solar system, Chi Cygnus would puff outward enough to roast Earth, Mars, and the asteroid belt.
These phases are referred to as the minima and maxima of a star. They happen to be particularly variable in Chi Cygnus, which has a maximum 17,000 times brighter than the minimum.
Intense it may be, but the brightening turns out not to be uniform over the surface of the star. The researchers used the Infrared Optical Telescope Array in Arizona to observe blotchy patterns bubbling through the outer layer, like the bright spots and dark lanes that make up the Sun's roiling granules. They published their findings December 10, 2009, in The Astrophysical Journal. "This work opens a window onto the fate of our Sun five billion years from now, when it will near the end of its' life," said author Sylvestre Lacoure of the Observatoire de Paris.
Fortunately there's plenty of time before the end to sit back and watch the preview for an awe-inspiring show.
—Jessa Forte Netting
S. Lacour, E. Thiébaut, G. Perrin, S. Meimon, X. Haubois, E. Pedretti, S. Ridgway, J.D. Monnier, J.P. Berger, P.A. Schuller, H. Woodruff, A. Poncelet, H. Le Coroller, R. Millan-Gabet, M. Lacasse, W. Traub. The Pulsation of ? Cygni Imaged by Optical Interferometry: a Novel Technique to Derive Distance and Mass of Mira Stars", Astrophysical Journal, Vol. 707, 635-643 (2009). Abstract [ADS] , Preprint [astro-ph] , press release.
For Further Study
Constellation, Cygnus, Light curves, Mira, Photosphere, Star, Sun, Supergranulation
Related Web Sites:
Infrared Optical Telescope Array (IOTA)
Chi Cygnus over time: http://www.cfa.harvard.edu/image_archive/2009/101/hires.jpg
Animation of Chi Cygnus' pulsing: http://www.cfa.harvard.edu/image_archive/2009/103/animation.mov