Posts Tagged ‘Cas A’

Echoes of a Death

Credit: NASA/JPL-Caltech/WISE Team


Supernovae explode with an energy that can outshine an entire galaxy. But just as quickly the star fades from view leaving an expanding bubble of star guts and in the case of Cassiopeia A, a light echo.

Explore this gorgeous image of the region surrounding the Cas A supernova remnant from NASA‘s Wide-field Infrared Explorer (WISE). What patterns or shapes do you see? Leave a note below.

About 11,000 years ago, toward the constellation Cassiopeia, the Queen, a massive supergiant star exploded in the Milky Way, our home galaxy. Supernova happen at the end of these giant stars’ lives. Stars about ten times more massive than our Sun burn through their hydrogen fuel quickly, within only tens of millions of years. They burn super hot and when the fuel runs out they collapse. Collapsing stars become even hotter and as the outer layers of the star heat up a runaway nuclear reaction can occur. The star explodes. The light from the explosion can be brighter than the entire galaxy. The explosion creates and scatters elements necessary for life on Earth, such as carbon and iron. It also spreads heavier elements such as gold, silver and uranium.

Zoom into the bright yellow cloud of dust. This is the bubble of material blown away from the star. As the edge of the bubble moves through interstellar space it heats up gas. The shockwave slams into the calm space at about 18,000 kilometers per second (11,000 miles per second) or about six percent the speed of light. In 11,000 years since the explosion, the expanding ball has expanded about 21 light-years.

Light travels much faster than the expanding bubble of gas and dust left over from the star. WISE, with its infrared eyes, detected infrared echoes of the brilliant flash as the light and heat ripple outward through surrounding star clouds. Look to the upper right for a curtain of orange in the cooler, greenish nebula. These orange echoes are remnants of heat generated when light from the explosion reached this part of the nebula.

Light from this explosion, traveling at more than six trillion miles per year, finally reached Earth in about 1667 AD. We have no record of it. European astronomers didn’t report it, Chinese astronomers didn’t record it. Scientists think that thick dust surrounding the star blocked most of the light, making it a dim supernova. Astronomers discovered the remnant in 1947. When they used new radio telescopes to scan the sky, Cas A was the brightest source they could see.

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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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Cassiopeia Fireworks

Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

In about 1667, a star about 10,000 light years from Earth exploded in the constellation Cassiopeia but it wasn’t noticed by astronomers on Earth. Today, images from NASA’s Hubble Space Telescope show the remnants of this fireworks display. Cassiopeia A, or Cas A, is one of the youngest supernova in the Milky Way Galaxy. Huge swirls of star debris glow as it moves through space.

The supernova may have been observed by astronomer John Flamsteed in 1680. Astronomy historians have shown that Flamsteed cataloged a star near the supernova’s location. However, he did not recognize it as a “new star,” or supernova. In the 1940s, using new radio telescopes, astronomers found that Cas A was the strongest radio source in the sky beyond the solar system. Finding the dim remnants of this expanding shell of gas and dust didn’t occur until 1950.

Supernova result after a massive star, much larger and heavier than our Sun, collapses under its own weight due to gravity. As the material rapidly falls toward the center, the gas ignites once again blowing the outer layers into space in an explosion that not only destroys the star but also briefly outshines an entire galaxy. In the cores of stars hydrogen atoms are fused together to make heavier elements such as helium. The resulting light and heat from this nuclear fusion process power the star. But elements are only created up to a certain point. To make elements heavier and more complex than oxygen, we need a supernova. Inside a supernova, with it’s intense heat, the rest of the elements that make up the Earth and our bodies, such as gold, silver, carbon and uranium are created. We are made of star stuff. Without supernova explosions, we could not exist.

Cas A is only 340 years old. Hubble has been tasked repeatedly to image the supernova remnant to track changes in its rapidly expanding filaments. Already the leftover bubble is more than 10 light-years across. Some of the material on the upper edge is moving at more than 50 million kilometers per hour. That is fast enough to travel from Earth to the Moon in 30 seconds. Look for the different areas of color in the Hubble image. Bright green filaments are rich in oxygen, red and purple are sulfur, and blue of hydrogen and nitrogen.

Do you see any patterns left over in the expanding cloud of gas and dust?


The ancient peoples saw pictures in the sky. From those patterns in the heavens, ancient storytellers created legends about heroes, maidens, dragons, bears, centaurs, dogs and mythical creatures...
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