Artist's impression of Chi Cygni. As the red giant star runs out of fuel, it pulses in and out, beating like a giant heart and ejecting shells of material.
Credit: ESO/L. Calçada
CAMBRIDGE: New images of the surface of a distant, dying star offer a preview of the ultimate fate of our own Sun, French scientists say.
"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 lead author Sylvestre Lacour of the Observatoire de Paris.
About 550 light-years from Earth, a star like our Sun is writhing in its death throes. Chi Cygni has swollen in size to become a red giant star so large that it would swallow every planet out to Mars in our solar system.
Moreover, it has begun to pulse dramatically in and out, beating like a giant heart.
Out of gas
As a Sun-like star ages, it begins to run out of hydrogen fuel at its core. Like a car running out of gas, its "engine" begins to splutter.
On Chi Cygni, we see those splutterings as a brightening and dimming, caused by the star's contraction and expansion. Stars at this life stage are known as Mira variables after the first such example, Mira "the Wonderful," discovered by David Fabricius in 1596.
As it pulses, the star is puffing off its outer layers, which in a few hundred thousand years will create a beautifully gleaming planetary nebula.
Chi Cygni pulses once every 408 days. At its smallest diameter of about 480 million kilometres, it becomes mottled with brilliant spots as massive plumes of hot plasma roil its surface.
As it expands, Chi Cygni cools and dims, growing to a diameter of 770 million kilometres - large enough to engulf and cook our solar system's asteroid belt.
Caught on camera
For the first time, astronomers have photographed these dramatic changes in detail. They reported their work in The Astrophysical Journal.
Since traditional telescopes lack the resolution required to image such distant stars, 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.
They used the Smithsonian Astrophysical Observatory's Infrared Optical Telescope Array, or IOTA, located at Whipple Observatory on Mount Hopkins, Arizona.
"IOTA offered unique capabilities," said co-author Marc Lacasse of the Harvard-Smithsonian Centre for Astrophysics. "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."
