James Webb reveals the secrets of light echo near the Cassiopeia A supernova remnants

The James Webb Space Telescope has captured the infrared glow of the Cassiopeia A supernova remnant, revealing unique structures resembling branches and curls of wood. When the core of the massive star collapsed, a powerful shock wave ripped the star apart. The wave created a bright pulse of X-ray and ultraviolet radiation that spread through space. After 350 years, this light reached interstellar matter, making it glow in the infrared spectrum. These observations allowed astronomers for the first time to create a three-dimensional model of interstellar dust and gas.

Image of light echoes near Cassiopeia A taken by James Webb’s NIRCam instrument. Photo: NASA

“We see layers like an onion. We think every dense, dusty region that we see, and most of the ones we don’t see, look like this on the inside. We just have never been able to look inside them before,” noted Josh Peek.

The team of scientists presented their findings at the American Astronomical Society conference in Maryland.

Light echo and its research

Images from the James Webb Telescope’s NIRCam have captured the phenomenon of light echo, an effect where the explosion or flare of a star illuminates the surrounding dust, causing it to glow. At visible wavelengths, this echo is due to light reflection. In the infrared spectrum, dust is heated and emits light.

These shimmering cosmic veils reveal interstellar gas and dust heated by the explosion of the ancient Cassiopeia A supernova outburst. The gas glows with infrared light in what is called a thermal light echo. When light from a supernova propagates through space at the speed of light, the echo seems to expand. The James Webb Space Telescope observed this light echo near the Cassiopeia A supernova remnant, creating a 3D scan of interstellar material. Photo: NASA

Previously, this phenomenon was observed with the Spitzer telescope. One of the light echoes was detected near Cassiopeia A. The light reflected by this echo comes from material behind Cassiopeia A, not from its remnants.

A NASA’s Spitzer Space Telescope photo highlights changes in phenomena called light echoes (colored areas) around the Cassiopeia A supernova remnant (center). The supernova remnant is 11,000 light-years away from Earth in the constellation Cassiopeia. The light echo is the largest ever seen, stretching more than 300 light-years from Cassiopeia A. When viewed from Earth, the entire frame takes up as much space as seven full moons. Photo: NASA

Images from the James Webb Telescope showed unique structures that have a scale of about 400 astronomical units, which surprised researchers that the structure is so small in scale. These structures probably interact with magnetic fields to form complex patterns similar to wood.

Spectroscopy and further research

The team’s science program includes spectroscopic observations with the MIRI instrument. The plan is to study the light echo over a long period of time, observing its evolution. This will help determine changes in the composition and state of interstellar dust. “We wanted to find out if molecules or even the smallest dust particles were destroyed by the intense radiation,” Jencson noted.

Infrared light echoes are a rare phenomenon that occurs under special conditions – a supernova explosion with a short pulse of energetic radiation. In the future, NASA’s Nancy Grace telescope will survey the galactic plane, which may help identify new infrared echoes for detailed study with the WEBB telescope. 

According to webbtelescope.org

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