Walking among the Stars

One of the most famous objects in the sky, the Cassiopeia A supernova remnant, can be seen like never before, thanks to NASA's Chandra X-ray Observatory, and Brown University. A three-dimensional virtual reality (VR) with augmented reality (AR) version of the 3D data allows you to walk inside the debris from a massive stellar explosion, select the parts of the supernova remnant to engage with, and access short captions on what the materials are.

Scientists combined data from Chandra, NASA's Spitzer Space Telescope, and ground-based facilities to construct a unique 3D model of the 300-year old remains of a stellar explosion that blew a massive star apart, sending the stellar debris rushing into space at millions of miles per hour. A collaboration with Brown University's Center for Computation and Visualization allowed the 3D astronomical data collected on Cassiopeia A, or Cas A for short, to be featured in the VR/AR program -an innovation in digital technologies with public, education, and research-based impacts.

Screen shot of the VR model being built. Colors assigned include jets in green; iron in blue; neon in yellow; cooler debris in purple; outer blast wave in red.

To create the 3D data visualization, Chandra scientists took advantage of both a previously known phenomenon, the Doppler effect, and a new technology that bridges astronomy and medicine. When elements created inside a supernova, such as iron, silicon and argon, are heated they emit light at specific wavelengths. The motion of the material Doppler-shifts the light so that material moving towards the observer is seen at shorter wavelengths and material moving away is seen at longer wavelengths. Since the amount of the wavelength shift is related to the speed of motion, one can determine how fast the debris are moving in either direction. Because Cas A is the result of an explosion, the stellar debris are expanding radially outwards from the explosion center. Using simple geometry, the scientists were able to construct a 3-D model using all of this information. A program called 3-D Slicer, modified for astronomical use by the Astronomical Medicine Project at Harvard, was used to display and manipulate the 3-D model.

This visualization shows that there are two main components to this supernova remnant: a spherical component in the outer parts of the remnant and a flattened (disk-like) component in the inner region. The spherical component consists of the outer layer of the star that exploded, probably made of helium and carbon. These layers drove a spherical blast wave into the diffuse gas surrounding the star. The flattened component — that astronomers were unable to map into 3-D prior to these recent observations — consists of the inner layers of the star. It is made from various heavier elements, not all shown in the visualization, such as oxygen, neon, silicon, sulphur, argon and iron.

High-velocity plumes, or jets, of this material are shooting out from the explosion in the plane of the disk-like component mentioned above. Plumes of silicon appear in the northeast and southwest, while those of iron are seen in the southeast and north. These jets were already known and Doppler velocity measurements have been made for these structures, but their orientation and position with respect to the rest of the debris field had never been mapped before now.

Cassiopeia A being converted for the cave or "Yurt" environment as well as the Oculus Rift.

The insight into the structure of Cas A gained from this 3-D visualization is important for astronomers who build models of supernova explosions. Now, they must consider that the outer layers of the star come off spherically, but the inner layers come out more disk-like with high-velocity jets in multiple directions.

The VR project is being made available in an open access format suitable for VR caves as well as on the Oculus Rift platform. Please contact Kimberly Arcand for more information on accessing those files. The project coordinators plan for a Google Cardboard version in future iterations. Additional data-driven 3D astronomical objects are also in the works for the Chandra VR/AR experience.

Additionally, Chandra has worked with the Smithsonian Learning Lab to create a browser-based interactive 3D application, and 360 degree video that works with Google Cardboard for Chandra's 3D Cas A object. The activity has related educational resources and activities at http://s.si.edu/cas-a

Or download the Cas A 3D model in a printable format at http://chandra.si.edu/deadstar/deadstar.html


Harvard-Smithsonian Center for Astrophysics Observatory Night Public Talk: Kimberly Arcand, CfA, Visualization Lead for NASA's Chandra X-Ray Observatory; Tom Sgouros, Manager of the Brown University Virtual Reality Lab

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Developed by the Chandra X-ray Center, at the Smithsonian Astrophysical Observatory, in Cambridge, MA, with funding by NASA under contract NAS8-03060