Walking among the Stars

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

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.

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.

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 also created a version that works with Google Cardboard or similar portable VR glasses and a smartphone connected to the Internet. To access that file, launch this URL on your smartphone (or iPod) in a browser window such as Safari. In that browser window, click the icon that looks like square glasses in the lower right of the page to put it in VR mode and place the phone/iPod in the Google Cardboard or similar portable VR glasses.

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

Or download the Cas A 3D model in a printable format at

Virtual reality is an immersive experience with three-dimensional information in a computer generated environment that can be interacted with using equipment such as goggles/headsets with sensors.

This VR demonstration was adapted from a "Yurt" or cave-like environment to a personal immersion experience with Oculus Rift. A less expensive Google Cardboard version is also being prepared.
Screenshot of Cassiopeia A being coded for a personal VR environment.


A new visualization provides an exceptional virtual trip – complete with a 360-degree view – to the center of our home galaxy, the Milky Way. This project, made using data from NASA's Chandra X-ray Observatory and other telescopes, allows viewers to control their own exploration of the fascinating environment of volatile giant stars and powerful gravity around the monster black hole that lies in the Galactic center.

The Earth is located about 26,000 light years, or about 150 trillion miles, from the center of the Galaxy. While humans cannot physically travel there, scientists have been able to study this region by using data from powerful telescopes that can detect light in a variety of forms, including X-ray and infrared light.

This visualization builds on infrared data with the European Southern Observatory's Very Large Telescope of 30 massive stellar giants called Wolf-Rayet stars that orbit within about 1.5 light years of the center of our Galaxy. Powerful winds of gas streaming from the surface of these stars are carrying some of their outer layers into interstellar space. When the outflowing gas collides with previously ejected detritus from other stars, the collisions produce shock waves, similar to sonic booms, which permeate the area. These shock waves heat the gas to millions of degrees, which causes it to glow in X-rays. Extensive observations with Chandra of the central regions of the Milky Way have provided critical data about the temperature and distribution of this multimillion-degree gas.

Astronomers are interested in better understanding what role these Wolf-Rayet stars play in the cosmic neighborhood at the Milky Way's center. In particular, they would like to know how the stars interact with the Galactic center’s most dominant resident: the supermassive black hole known as Sagittarius A* (abbreviated Sgr A*). Pre-eminent yet invisible, Sgr A* has the mass equivalent to some four million Suns.

The Galactic Center visualization is a 360-degree movie that immerses a viewer into a simulation of the center of our Galaxy. The viewer is at the location of Sgr A* and is able to see about 20 massive stars (white, twinkling objects) orbiting Sgr A* as they continuously eject stellar winds (black to red to yellow color scale). These winds collide with each other, and then some of this material spirals towards Sgr A*. The movie, which starts 350 years in the past, spans 500 years.

The researchers, led by Christopher Russell of the Pontifical Catholic University of Chile, used the visualization to understand the presence of a previously-detected ring of X-rays that extends about 0.6 light years outward from Sgr A*. The information provided by the visualization and the theoretical modeling led Russell and his colleagues to determine that Sgr A* had a relatively powerful outburst that started within the last few centuries. Moreover, their findings suggest the outburst from the supermassive black hole is still affecting the X-ray emission around Sgr A* even though it ended about one hundred years ago.

The 360-degree video of the Galactic Center is ideally viewed in virtual reality (VR) goggles, such as Samsung Gear VR or Google Cardboard. The video can also be viewed on smartphones using the YouTube app. Moving the phone around pans to show a different portion of the movie, mimicking the effect in the VR goggles. Most browsers on a computer also allow 360-degree videos to be shown on YouTube. To look around, either click and drag the video, or click the direction pad in the corner.


The region of the Milky Way's center about 26,000 light years from Earth.
(Credit: NASA/CXC/Pontifical Catholic Univ. of Chile /C.Russell et al.)


Please take our quick survey and let us know what you think:

Press release for Cas A VR:

Photo release for Galactic Center 360:


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Creator/Manager: Kimberly Arcand
Art Direction/Design: Kristin DiVona
Web Developer: Khajag Mgrdichian

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