Webb sees shockwave continuing hundreds of years after supernova blast

Scientists have probed the remains of a star that died in a violent supernova and discovered that its shockwave continued reverberating through space, hundreds of years later.

That shockwave eventually reached interstellar space, the medium that fills regions between stars. Researchers used the James Webb Space Telescope, a collaboration of NASA and its European and Canadian counterparts, to find that the ancient pulse, like a cosmic flashlight, had lit up never-before-seen details in the otherwise mysterious material.

“We see layers like an onion,” said Josh Peek of the Space Telescope Science Institute in Baltimore, a member of the research team, in a statement. “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.”

Interstellar space is full of gas and dust clouds, but they’re often invisible unless something illuminates them. This interstellar material is thought to consist of several elements: leftover ingredients from galaxy formation, star debris, and the building blocks for future stars and planets. Scientists want to study this stuff to understand the structure of galaxies and the life cycles of stars.

The shockwave Webb studied emerged from Cassiopeia A, now a neutron star, about 11,000 light-years from Earth. After the massive star collapsed, the pulse surged from its core outward, shooting X-rays and ultraviolet light through space. 

Some 350 years later, it traveled through interstellar clouds, causing them to glow in infrared light. The phenomenon is what’s known as a light echo. Light echoes at visible wavelengths are due to light reflecting off interstellar material. Light echoes at infrared wavelengths are caused when energetic radiation warms dust that then glows. The latter are rare because they require a special kind of supernova to occur, astronomers say.

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Webb was built to detect invisible light at infrared wavelengths. Dust and gas in space obscure the view to extremely distant and inherently dim light sources, but infrared waves can pierce through the clouds. One Webb scientist likened the strength of the telescope to being able to sense the heat of a single bumblebee on the moon.

The new images have allowed astronomers to map the 3D structure of interstellar gas and dust for the first time. In particular, the researchers learned that the interstellar medium had surprisingly small, sheet-like features and dense knots. Both are thought to be related to magnetic fields. 

The findings were presented at the 245th meeting of the American Astronomical Society in Maryland.

“Even as a star dies,” said outgoing NASA administrator Bill Nelson, “its light endures — echoing across the cosmos.”