Close-up look at dying star show our sun's fate

Posted By Cameron On December 15, 2009 - 3:50pm
Close-up look at dying star show our sun's fate

For the first time, astronomers have photographed these dramatic changes in detail. They reported their work in the December 10 issue of The Astrophysical Journal.

"We have essentially created an animation of a pulsating star using real images," stated Lacour. "Our observations show that the pulsation is not only radial, but comes with inhomogeneities, like the giant hotspot that appeared at minimum radius."

Imaging variable stars is extremely difficult, for two main reasons. The first reason is that such stars hide within a compact and dense shell of dust and molecules. To study the stellar surface within the shell, astronomers observe the stars at a specific wavelength of infrared light. Infrared allows astronomers to see through the shell of molecules and dust, like X-rays enable physicians to see bones within the human body.

The second reason is that these stars are very far away, and thus appear very small. Even though they are huge compared to the Sun, the distance makes them appear no larger than a small house on the moon as seen from Earth. Traditional telescopes lack the proper resolution. Consequently, the team turned to a technique called interferometry, which involves combining the light coming from several telescopes to yield resolution equivalent to a telescope as large as the distance between them.

This movie combines infrared images of the surface of Chi Cygni, obtained with IOTA, with visual brightness measurements provided by the American Association of Variable Star Observers. Chi Cygni demonstrates a 408-day-period of expanding and dimming, followed by contracting and brightening.

(Photo Credit: Sylvestre Lacour, Observatoire de Paris)

They used the Smithsonian Astrophysical Observatory's Infrared Optical Telescope Array, or IOTA, which was located at Whipple Observatory on Mount Hopkins, Arizona.

"IOTA offered unique capabilities," said co-author Marc Lacasse of the Harvard-Smithsonian Center for Astrophysics (CfA). "It allowed us to see details in the images which are about 15 times smaller than can be resolved in images from the Hubble Space Telescope."

The team also acknowledged the usefulness of the many observations contributed annually by amateur astronomers worldwide, which were provided by the American Association of Variable Star Observers (AAVSO).

In the forthcoming decade, the prospect of ultra-sharp imaging enabled by interferometry excites astronomers. Objects that, until now, appeared point-like are progressively revealing their true nature. Stellar surfaces, black hole accretion disks, and planet forming regions surrounding newborn stars all used to be understood primarily through models. Interferometry promises to reveal their true identities and, with them, some surprises.

Chi Cygni changes brightness dramatically and regularly every 408 days due to in-and-out pulsations. Using interferometry to image the star's surface at four separate times, astronomers found that the star grows to a diameter of 480 million miles -- large enough to engulf the asteroid belt -- before shrinking to a minimum diameter of 300 million miles. Chi Cygni also shows significant hotspots near minimum radius.

(Photo Credit: Sylvestre Lacour, Observatoire de Paris)

Interferometric observations by SAO's Infrared Optical Telescope Array, shown here, demonstrated that the red giant star Chi Cygni spans at least 300 million miles, large enough to swallow the planet Mars if it were at the center of our solar system. Interferometry combines signals from several telescopes to yield a sharp resolution equivalent to a single, giant telescope.

(Photo Credit: CNRS / Observatoire de Paris)

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