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Walking Through an Exploded Star: Rendering Walking Through an Exploded Star: Rendering Supernova Remnant Cassiopeia A into Virtual Reality Resources Kimberly Kowal Arcand Megan Watzke Keywords Smithsonian Astrophysical Observatory/ Smithsonian Astrophysical Observatory/ Data, virtual reality, science communication, Chandra X-ray Observatory Chandra X-ray Observatory visualisation, augmented reality, narrative [email protected] [email protected] Elaine Jiang Tom Sgouros Brown University Brown University [email protected] [email protected] Sara Price Peter Edmonds Smithsonian Astrophysical Observatory/ Smithsonian Astrophysical Observatory/ Chandra X-ray Observatory Chandra X-ray Observatory [email protected] [email protected] Data on the Cassiopeia A supernova remnant from NASA and other sources have been rendered into a three-dimensional virtual reality (VR) and augmented reality (AR) programme, which is the first of its kind. This data-driven experience of a supernova remnant allows viewers to take a virtual walk inside the leftovers of a massive star that has exploded, select parts of the remnant to engage with and access descriptive texts on what the different materials are. This programme is based on a unique three-dimensional (3D) model of the 340-year old remains of a stellar explosion, made by combining data from NASA’s Chandra X-ray Observatory, the Spitzer Space Telescope and ground-based facilities. A collaboration between the Smithsonian Astrophysical Observatory and Brown University allowed the 3D astronomical data collected on Cassiopeia A to be featured in the VR/AR programme, which is an innovation in digital technologies with public, education and research-based impacts. Introduction more user-friendly technologies, presents to work with specific cases to practice the new opportunities for their use in science applicable caregiving skills (Murphy, 2018). Overview of Virtual Reality (Ferrand et al., 2016). There is a poten- tial for VR to revolutionise how experts — Beyond the universe of the body and out Virtual reality (VR) is a computer technol- from molecular modelling to environmental into the Universe at large, astronomical ogy that simulates a user’s physical pres- conservation — visualise and analyse their data sets often provide high-resolution, ence in a virtual environment. VR’s close data and how that data is then communi- multi-wavelength and multi-dimensional relative, augmented reality (AR), adds ele- cated to non-experts (Isenberg, 2013). (lately, even multi-messenger) informa- ments such as text, overlays and audio tion. The process of converting photons, to enhance that experience with sensory In medicine alone, VR is a unique tool for or packets of energy, into 2D images has input and is briefly discussed on page 19. data visualisation and comprehension as been documented and studied (Rector et VR has existed in some form since the well as for continuing education and user al., 2017; Arcand et al., 2013; DePasquale 1980s (Faisal, 2017). Though it has faced experiences. Uses of VR programmes et al., 2015; Rector et al., 2007) but the many ups and downs (Stein, 2015), includ- that are in development and implementa- translation of that information into 3D forms ing the unrealised promise of a Virtual tion range from improving health workers’ that use human perspective, cognition Reality Markup Language in the late 1990s, understanding of brain damage (Hung et and stereoscopic vision, less so (Ferrand it has become more commonplace in the al., 2014) to implementing virtual surgery et al., 2016). Since the Universe is multi- consumer market since about 2010 (Faisal, training for medical students (Murphy, dimensional itself, as Fluke and Barnes 2017)1. Given its potential for improving the 2018) and applying VR and AR techniques (2016) ask: “Are we making the best use gaming industry, media and even adult in an accessible way in the treatment of of the astronomer’s (and a non-expert’s) entertainment, there are major commer- Alzheimer’s disease (Garcia-Betances et personal visual processing system to dis- cial driving forces behind the technology’s al., 2015). VR has been shown to improve cover knowledge?” development (Oracle, 2016; CNET, 2016). upon the traditional tangible model of using dummies to enhance medical stu- Astronomical VR experiences include The increased commercial prominence of dents’ preparation for assisting patients exploring exoplanets (planets outside our these technologies, including the availabil- in high-risk real-life scenarios. It can allow Solar System) through science-informed ity of less expensive yet good quality and physicians and other health professionals 3D artists’ impressions converted into CAPjournal, No. 24, October 2018 17 Walking Through an Exploded Star: Rendering Supernova Remnant Cassiopeia A into Virtual Reality Figure 1. Cassiopeia A (Cas A) is a supernova remnant located about 10 000 light Figure 2. By combining data from Chandra, the Spitzer Space Telescope and years from Earth. This 2D visual representation of Cas A has been processed to ground-based optical observations, astronomers were able to construct the first show with clarity the appearance of Cas A in different bands of X-rays. This will aid 3D fly-through of a supernova remnant. This 3D visualisation (shown here as a still astronomers in their efforts to reconstruct details of the supernova process such image) was made possible by importing the data into a medical imaging pro- as the size of the star, its chemical make-up and the explosion mechanism. The gramme that has been adapted for astronomical use. Commercial software was colour scheme used in this image is the following: low-energy X-rays are red, medium- then used to create the 3D version of the data. The green region shown in the energy ones are green and the highest-energy X-rays detected by Chandra are image is mostly iron observed in X-rays; the yellow region is mostly argon and sili- coloured blue. The image is 8.91 arcmin across (or about 29 light years). con seen in X-rays, optical and infrared, and the red region is cooler debris seen in Credit: NASA/CXC/SAO the infrared. The positions of these points in three-dimensional space were found by using the Doppler effect and simple assumptions about the supernova explo- sion. Credit: NASA/CXC/MIT/T.Delaney et al. VR2; experiencing a NASA mission space- from Chandra, infrared data from Spitzer nant containing light elements like helium craft in VR such as the James Webb Space and optical data from ground-based tele- and carbon from the outer layer of the Telescope3; walking across the surface of scopes. In Figure 1, the green regions are exploded star and a flattened (disc-like) Mars4; exploring dozens of massive stars mostly iron, the yellow regions include a component in the inner region containing from the perspective of the supermassive combination of argon and silicon, the red heavier elements like argon and iron from black hole at the centre of our Galaxy5 regions are cooler explosion debris and the the inner layers of the star7. The blue fila- (Russell, 2018); and viewing radio data blue regions show the outer blast wave. ments indicating the blast wave show a dif- cubes of a spiral galaxy (Ferrand et al., ferent type of radiation that does not emit 2016). When elements created inside a supernova light at discrete wavelengths, and, there- are heated, they emit light at specific wave- fore, have not been included in the 3D Data Path for Cassiopeia A: From 2D lengths. Because of the Doppler effect, model. to VR elements moving towards the observer will have shorter wavelengths and elements High-velocity jets of heavy material shoot Supernova explosions are among the most moving away will produce longer wave- out from the explosion in the plane of the violent events in the Universe. When the lengths. Since the extent of the wavelength disc-like component mentioned above. nuclear power source at the centre of a shift is related to the speed of motion, the Jets of silicon appear in the upper left massive star is exhausted, the core col- velocity of the debris can be determined and lower right regions, while plumes of lapses and in less than a second, a neutron by analysing the light. By combining this iron are seen in the lower left and northern star typically forms. This process releases Doppler information with the expectation regions. These had been studied before an enormous amount of energy, which that the stellar debris expands radially out- the 3D model was made, but their orien- reverses the implosion, blows material out- wards from the explosion centre, Delaney tation and position with respect to the rest wards and produces a brilliant visual out- et al. (2010) used simple geometry to con- of the debris field had not been mapped burst. The resulting debris field is referred struct a 3D model of Cas A (Figure 2). A before. to as a supernova remnant. programme called 3D Slicer — modified for astronomical use by the Astronomical The insight into the structure of Cas A Cassiopeia A (Cas A) is a supernova rem- Medicine Project at Harvard — was used gained from this 3D visualisation is impor- nant from an explosion that occurred to display and manipulate the 3D model6. tant for astronomers who build models of approximately 340 years ago in the Earth’s supernova explosions. They have learned timeframe (Figure 1). A multi-wavelength The visualisation shows that there are two that the outer layers of the star come off three-dimensional (3D) reconstruction of main components to Cas A: a spherical spherically, but the inner layers come out this remnant was created using X-ray data component in the outer parts of the rem- more disc-like with high-velocity jets in 18 CAPjournal, No. 24, October 2018 CAPjournal, No. 24, October 2018 AR has become popular because of the number of smartphones, wearable com- puting devices and other smart gadgets being pushed in the consumer market (Vogt & Shingles, 2013; Amer & Peralez, 2014).
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