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Thousands of years ago, a star in our galaxy exploded violently and created a glowing supernova remnant called Cassiopeia A that scientists have been talking about for years.
Now, a new image captured by the James Webb Space Telescope has revealed the closest and most detailed look at the exploding star, according to astronomers. Analyzing the image could help researchers better understand the processes that drive these massive combustion events.
The space observatory also allowed the astronomers to glimpse mysterious features that are not visible in images taken of the relic using telescopes such as Hubble, Chandra or Spitzer or other Webb instruments.
First lady Dr. Jill Biden shared the new image on Monday as she debuted the White House’s digital Advent Calendar, which includes Webb’s new perspective on Cassiopeia A that appears to glow like a Christmas ornament.
“We’ve never had this kind of view of an exploding star before,” astronomer Dan Milisavljevic, an assistant professor of physics and astronomy at Purdue University, said in a statement. “Supernovae are the main drivers of cosmological evolution. The energy, the chemical abundance — so much depends on our understanding of supernovae. This is our closest look at a supernova in our galaxy.”
The gas and dust pulse consists of all the stars that went supernova 10,000 years ago. Cassiopeia A is located 11,000 light years away in the constellation Cassiopeia. A light year, equal to 5.88 trillion miles (9.46 trillion kilometers), is how far a beam of light travels in one year.
The light from Cassiopeia A first reached Earth about 340 years ago. As the youngest supernova remnant in our galaxy, the celestial object has been studied by numerous ground and space-based telescopes. The remnant stretches for about 10 light-years across, or 60 trillion miles (96.6 trillion kilometers).
Insights from Cas A, as the remnant is also known, allow scientists to learn more about the life cycle of stars.
See turn A in a new light
Astronomers used Webb’s Near-Infrared Camera, called NIRCam, to see the supernova remnant at different wavelengths of light than those used in previous observations. The image shows unprecedented detail of the interaction between the expanding shell of material created by the supernova as it collides with the gas released by the star before the explosion.
But the image looks completely different from the one Webb took in April using the telescope’s Mid-Infrared Instrument, or MIRI. In each image, certain features stand out that are invisible in the other.
Webb views the globe in infrared wavelengths of light, which are invisible to the human eye. As Webb scientists process the data, the light captured by the telescope is converted into a spectrum of colors visible to humans.
The highlight of the new NIRCam image are orange and light pink flashes within the inner shell of the supernova remnant. The colors correspond to the gaseous knots of elements lost by the star, including oxygen, argon, neon and sulphur. Mixed within the gas are dust and molecules. Eventually, all these ingredients will combine to form new stars and planets.
Studying the remnant allows scientists to reconstruct what happened during the supernova.
“With the resolution of NIRCam, we can now see how the dying star completely broke apart when it exploded, leaving behind filaments like small pieces of glass,” said Milisavljevic. “It’s incredible that after all these years of studying Cas A these details can now be resolved, giving us a game-changing view of how this star exploded.”
Webb’s dual perspective
When comparing the NIRCam image to the MIRI image taken in April, the new view appears to be less colorful. The bright orange and red colors from the April image look further through NIRCam’s eyes, showing where the shock wave from the supernova crashed into the surrounding material.
The white light in the NIRCam image is due to synchrotron radiation, which is created when charged particles accelerate and travel around magnetic field lines.
A key feature missing from the NIRCam view is the “Green Monster” from the MIRI image, or a circle of green light in the center of the relic, which has confused and challenged the astronomers.
But new details can be seen in the near-infrared image that shows circular holes interspersed in white and purple, naming charged particles of debris that shape the gas shed by the star before it explodes.
Another new feature in the NIRCam image is a blob called Baby Cas A visible in the lower-right corner, which appears to be an offshoot of the larger supernova remnant and is located 170 light-years behind Cassiopeia A.
Baby Cas A is a feature known as a light echo, where the supernova’s light interacted with dust and caused it to heat up. The dust continues to glow as it cools over time.
“It’s amazing,” said Milisavljevic, who led a project team that contributed to the new image. “Some features have emerged that are completely new – that will change the way we think about stellar lifetimes.”
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