Astronomers detect coldest ever companion of a Sun-like star
By ANITuesday, December 8, 2009
WASHINGTON - Astronomers at the Max Planck Institute for Astronomy have discovered and directly imaged a faint celestial body that orbits the star GJ 758, which at a temperature of around 330 degrees Celsius, is the coldest companion of a Sun-like star ever to be directly imaged.
Known as GJ 758 B, the object’s mass is estimated to be between 10 and 40 Jupiter masses.
Images provide valuable information on the orbit of the planet, its temperature and the chemical composition of its atmosphere.
In the search for extrasolar planets, astronomers have succeeded in recording such an image with a new instrument - and even struck it lucky during the first observations.
The camera, called HiCIAO, is installed on the 8-metre Subaru telescope on Mauna Kea in Hawaii. he researchers used the latest adaptive optics to remove the blur caused by air turbulences.
Although on every individual image, the tiny signal of the planet is drowned out by the residual halo of the central star, the clever combination of time sequences of individual images, so-called “Angular Differential Imaging” (ADI), enabled astronomers to suppress the halo of the central star to such an extent that the weak glow of the companion GJ 758 B was visible in the final image.
Before this discovery, only ten possible exoplanets had been imaged directly.
Compared to the other candidates, GJ 758 B has much more in common with the large bodies in our planetary system.
It orbits a Sun-like star at a distance that corresponds to those of the outer solar planets.
The distance to its central star is roughly the same as the distance between Neptune and the Sun.
The overall dimensions of the orbit of GJ 758 B can only be estimated from the data available, however.
Most probable is an average separation from the central star of 59 astronomical units (corresponding to 8.85 billion kilometres).
Particularly interesting is the relatively low temperature of the supposed planet, which is between 280 and 370 degrees Celsius.
“This corresponds to the temperature of an oven or that of the sun-facing side of the planet Mercury,” said Christian Thalmann from the Max Planck Institute for Astronomy in Heidelberg, first author of the publication.
“GJ 758 B is therefore the coldest companion of a Sun-like star ever to be imaged directly,” Thalmann added. (ANI)
