HR 8799 and the Vortex Coronagraph

(source)

This is a pretty cool picture--one that I think really is worth its own post. It's a direct image of the three planets known to orbit the star HR 8799. HR 8799 is an exceptionally young star--just 30 million years old or so--and it is still surrounded by an enormous dust halo over 2000 AU in diameter. This cloud of dust is apparently so thick that it threatens the stability of this young solar system. and could be the subject of a post all its own. However, it is not the subject of this post. The three planets known to orbit inside of it are (actually, there are four--but one is too close in to directly image yet) .

Those three imageable planets were among the first directly imaged, using the Keck telescopes in 2008, observed using adaptive optics in infrared. But the image we're concerned with here is an entirely different image, taken just last year. What is remarkable about it is that it was taken using an instrument called a vortex coronograph (a coronograph is a device used to block out the light from a star in order to observe things near to it), and that that instrument was attached to portion of the Hale telescope just 1.5 meters in diameter. While by no means a small telescope, this is an astonishingly small aperture to be producing direct images of exoplanets. Coronographs have been used since before exoplanets were even known to exist, when observing our own Sun. However, a significant amount of light has always been able to creep around the dot that blocks it in traditional coronographs, making direct imaging of planets around distant stars extremely difficult. The vortex coronograph evidently solves this problem by using a spiral pattern to obscure the star, blocking its light almost entirely while allowing all of the light from any planets it may have to pass through. And if it is as effective as it seems, it may mean that direct imaging of exoplanets, still responsible for just a handful of exoplanet detections, could become an increasingly viable way of discovering planets--one which might be able to tell us more about the nature of those planets than we have yet been able to discern.

The original direct image of the HR 8799 system, taken using the Keck Telescopes--which are ten times the diameter of the mirror used to produce the image at the start of this post (source).