NASA has revealed an interesting new device that can be used to directly image planets around other stars. Called a vortex coronagraph, or vortex mask, it is made out of synthetic diamond and measures just 1 centimeter (0.4 inches) across and 0.3 millimeters (0.01 inches) thick.
“The vortex's engraved pattern of grooves is very similar to a compact disk, making it look like a miniature version of a CD,” said NASA. Zooming on the device with a scanning electron microscope reveals the mask's microstructure, which looks like a series of concentric grooves, each about 100 times smaller than a human hair.
So, how does it work? Well, stars outshine their planets by a factor of a few thousand to a few billion, depending on their orbits and size, which makes seeing planets quite difficult. To get around this, astronomers sometimes use a coronagraph to block out the light of the star.
However, regular coronagraphs are limited in that they struggle to see planets that are close to their host star. The vortex coronagraph improves on this by redirecting light away from a telescope’s detectors, rather than simply blocking it, by combining and canceling light waves.
"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 Dmitri Mawet, a research scientist from NASA’s Jet Propulsion Laboratory (JPL) and Caltech in California.
The vortex coronagraph (left) looks a bit like a CD, but has concentric rings when viewed up close (right). University of Liège/Uppsala University
The device was used for the first time recently, having been installed on the W. M. Keck Observatory in Hawaii. One team, led by Gene Serabyn from JPL, used it to directly image a brown dwarf (a failed star) called HIP79124 B, which orbits 23 AU from its host star (1 AU, astronomical unit, is Earth’s distance from the Sun).
A second study, led by Mawet, observed three rings of dusty material around a young star called HD141569A. This material will eventually form planets in the system, and understanding how these disks evolve is important in increasing our knowledge of planet formation. The researchers found that the innermost ring had a temperature of about -173°C (-280°F), a bit warmer than our asteroid belt.
The plan is for the device to look at many more young planetary systems in the future, including planets near “frost lines”, where water can exist as ice and also thought to be the boundary between rocky and gas planets. Doing so may help answer how gas giants in other systems are found so close to their stars in some instances, something that has puzzled astronomers.
"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.