A Bubble of Many Colors

Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech/Steward/O.Krause et al.


Supernova remnant Cassiopeia A glows with many colors in this composite image from NASA’s Great Observatories.

Zoom into the jumbled strands of colors. What stories or pictures do you see? Leave a note below.

Cassiopeia A, or Cas A, is the remnant of a star that exploded. Supernovae are the ultimate end of stars that are about ten times more massive than our Sun. When stars this big run out of hydrogen fuel, they quickly expand. Their great gravity however pulls the material back in toward the star where it heats up very fast creating a runaway nuclear fusion reaction. The star becomes unstable and explodes.

As you explore the image, look for the different colors offered by images of each observatory. Astronomers used to think that the explosion scattered material evenly around the star. But knots and filaments show that material was ejected at different times and speeds. Spitzer imagery shows reddish warm dust in the outer shell of the supernova with a comfortable temperature of about 80 degrees Fahrenheit (10 degrees Celsius). Hubble Space Telescope imagery shows a fine yellow filament structure of warmer gases. Chandra imagery shows superhot gas in blues and greens. The hot gas was created when material ejected at high speed during the explosion slammed into the calm gas and dust surrounding the star. Look for the turquoise dot near the center of the image. This may be the neutron star created during the supernova. A neutron star is the hot and super-dense core of an exploded star. Some scientists believe that a black hole resides at the center of the remnant.

Cas A lies about 11,000 light-years from the Earth toward the constellation Cassiopeia. Astronomers believe first light from the supernova reached Earth about 300 years ago. But no one on Earth seems to have seen it. Historians think that John Flamsteed may have noticed the star in 1680. Astronomers theorize that the massive star had ejected a dense bubble of dust that blocked light from the explosion. Scientists discovered the supernova in the 1940s because it is one of the brightest radio sources in the sky. No supernovae have been visible in the Milky Way since.

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