Thursday, May 19, 2011

Exoplanets without a star: galaxy teems with lonely Jupiters

Seems like every week astronomers find a new exoplanet, one that's the biggest or the smallest or the hottest or most habitable. However, this week astronomers are announcing a truly unique and new class of exoplanets: Jupiter sized planets that are in extremely large orbits or completely unbound from a host star altogether. And there appear to be a lot of them, as these planets seem to be more common than main sequence stars.

Finding a planet that is not associated with a star is no easy task. In the new search, a team of researchers used a technique called gravitational microlensing. As you look at a background field of stars, if an object passes between you and one of the stars, there will be a temporary brightening of that star. This occurs as the gravity of the object bends light around itself, which acts as a lens for light from the background star, hence “gravitational lensing." Microlensing occurs when the foreground object is too small to create measurable distortion of the background star and only a brightening is observed. This makes it an ideal detector for small, dim objects.

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