2023-05-05 10:15:04
The supernova-like explosion of a star is a spectacular event, but the debris left behind by the catastrophe can be even more spectacular.
A new image captured in the mid-infrared band by the James Webb Space Telescope provides an impressive example of this. The image shows the remnants of the Cassiopeia A (Cas A) supernova, which were created by a stellar explosion that was sighted from Earth 340 years ago. Cassiopeia A is the youngest known remnant of the explosion of a massive star in our galaxy, making it a unique opportunity to learn more about how supernovae like this are produced.
“Cassiopeia A represents our best chance to look at the debris field after a star exploded and to do a kind of stellar autopsy to understand what kind of star was there before and how that star exploded,” explains Danny Milisavljevic, from Purdue University in West Lafayette, Indiana, United States, a member of the team that led these observations.
“Compared to previous infrared images, we see incredible detail that we haven’t been able to access before,” added Tea Temim of Princeton University in New Jersey, also on the team.
Cassiopeia A is a typical supernova remnant that has been extensively studied by various ground-based and space-based observatories, including NASA’s Chandra X-ray Observatory. Observations at different wavelengths can be combined to provide a more complete understanding of this remnant.
Cassiopeia A, the landscape that remains three centuries after the explosion that annihilated a star. (Photo: NASA, ESA, CSA, D. Milisavljevic (Purdue), T. Temim (Princeton), I. De Looze (Ghent University). Image processing: J. DePasquale (STScI))
The striking colors of the new image of Cassiopeia A, in which infrared light is translated into wavelengths of visible light, contain a wealth of scientific information that the team is beginning to unravel. On the outside of the bubble, there are curtains of material colored orange and red due to the emission of hot dust. This marks where the material ejected from the exploding star collides with the surrounding circumstellar gas and dust.
Inside this outer shell are bright pink mottled filaments that are dotted with clumps and knots. This represents the material from the star itself, which shines due, among other things, to a mixture of various chemical elements (heavier than hydrogen and helium), such as oxygen, argon and neon.
“We are still trying to unravel all these sources of emissions,” clarifies Ilse De Looze, from the University of Ghent in Belgium, of the research team.
Stellar material can also be seen, appearing as fainter wisps near the interior of the cavity.
Perhaps most prominent is a loop, depicted in green, that runs along one side of the central cavity. “We have nicknamed him the ‘Green Monster’ (green monster) in honor of Fenway Park in Boston. When looking closely, it is observed that it is full of marks of what appear to be mini bubbles”, explains Milisavljevic. “The shape and complexity are unexpected and difficult to understand.”
The origins of cosmic dust… and of us
Among the scientific questions that Cassiopeia A can help answer is the following: where does cosmic dust come from? Observations have found that even very young galaxies in the early universe are bathed in massive amounts of dust. It is difficult to explain the origins of this dust without resorting to supernovae, which spew large amounts of heavy elements (the building blocks of dust) through space.
However, existing observations of supernovae have not been able to conclusively explain the amount of dust we see in those early galaxies. By studying Cassiopeia A with the Webb Space Telescope, astronomers hope to gain a better understanding of its dust content, which could help yield insightful new insights into where the building blocks of planets and ourselves are created.
“In Cassiopeia A, we can spatially resolve regions that have different gas compositions and look at what types of dust formed in those regions,” explains Temim.
Supernovae like the one that formed Cassiopeia A are crucial to life as we know it. They spread chemicals, like the calcium we find in our bones and the iron in our blood, through interstellar space, seeding new generations of stars and planets.
“By understanding the process of the explosion of stars, we are reading the story of our own origin,” Milisavljevic stresses. “I’m going to spend the rest of my career trying to understand what’s in this data set.”
The Cassiopeia A remnant spans about 10 light-years across and lies 11,000 light-years away in the constellation Cassiopeia.
The James Webb Space Telescope (JWST) is the result of an international collaboration led by NASA, ESA and CSA, respectively the US, European and Canadian space agencies. (Source: NASA)
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