New exoplanet beauty shots made by redirecting starlight into the eye of an optical storm

Jessica Hall
Not long ago, the ESO partnered up with Breakthrough Starshot to upgrade the VLT into a sleek exoplanet-hunting beast. Not to be outdone, the Keck Observatory in Hawaii has just released the first batch of images taken with its shiny new telescope hardware upgrade. The upgrade is called a vortex coronagraph, and scientists are using it to take a closer — and clearer — look at distant planets as they form.
Looking at exoplanets directly is hard, partly because they’re far away, but also because the candlepower coming from a host star so hilariously outshines any light that manages to reflect off the planet and still make it back into our telescopes. We have a similar problem trying to look at the sun, because the insane dynamic-range difference makes most cameras lose a lot of performance. Astronomers often address this problem using an instrument called a coronagraph, which relies on a mask: a low-tech solution that physically obstructs photons from hitting the lens or CCD. We use coronagraphs, for example, to blot out the sun so we can look at coronal mass ejections.
But the vortex coronagraph doesn’t use a mask. No, they zipped right past a physical occlusion and went straight to adaptive optics. Instead of obstructing photons, the vortex coronagraph “redirects” them away from the camera “using a technique in which light waves are combined and canceled out.” Dmitri Mawet, who developed the vortex coronagraph, compares the process with what happens at the eye of a storm.
“The instrument is called a vortex coronagraph because the starlight is centered on an optical singularity, which creates a dark hole at the location of the image of the star,” said Mawet, of Caltech and the JPL. “Hurricanes have a singularity at their centers where the wind speeds drop to zero—the eye of the storm. Our vortex coronagraph is basically the eye of an optical storm where we send the starlight.”
“The three rings around this young star are nested like Russian dolls and undergoing dramatic changes reminiscent of planetary formation,” said Mawet. “We have shown that silicate grains have agglomerated into pebbles, which are the building blocks of planet embryos.” This image was captured using the vortex coronagraph, on NIRC2, the main infrared telescope at Keck.
But wait: there’s more. Because the vortex doesn’t require a mask, it has the advantage of not losing a region of the visual field to parallax problems created by artifacts at the edges of the mask. It might only be a sliver on the viewfield, but parallax means that the tiny warped region on the telescope accounts for a good-sized slice of space that we can see more clearly now. The newly souped-up NIRC2 telescope has already delivered a batch of images, and the ensuing science has been reported in The Astronomical Journal.
Researchers from the University of Liège, led by Olivier Absil, designed part of the Keck vortex coronagraph called the phase mask. The phase mask is the part that actually does the redirecting of photons: it consists of “concentric microstructures that force the starlight waves to swirl about the mask’s center, creating the vortex singularity,”Absil said. The design went from the States to Liège, and then to Uppsala University, where it was forged by Mikael Karlsson and his team. Karlsson and colleagues etched the concentric microstructures into a slice of synthetic diamond in a plasma chamber, under bombardment by argon and oxygen ions. That process “rips” carbon atoms out of the diamond lattice, providing nearly single-atom etching resolution.
The phase mask itself. Image: NASA/JPL
In the future, scientists intend to use their new pet vortex to look at many more young planetary systems, particularly planets near the so-called snow line around their parent star. The snow line is the distance away from a star at which the radiant temperature has fallen far enough for volatile molecules like water to condense into solid grains. Using the vortex to look at the snow line may also help us better understand the inflection points that mark the places where rocky planets form, versus gas giants.
Of particular interest are gas giants tucked right in close to their host stars: the fabled “hot Jupiters.” Did they form out past the snow line and drift inward, or did they form right there where they are? “With a bit of luck, we might catch planets in the process of migrating through the planet-forming disk, by looking at these very young objects,” said Mawet. Observations like that stand a good chance of answering some important questions about (the origins of) life, the universe, and everything.
New exoplanet beauty shots made by redirecting starlight into the eye of an optical storm Reviewed by Bizpodia on 00:02 Rating: 5

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