Webb captures the light echoes of an exploding star

Many decades ago, a massive star collapsed. A shockwave erupted, tearing the star apart. As this shockwave hit the star’s surface, it created a burst of intense X-rays, ultraviolet light, and a powerful light echo.

This pulse traveled across space, and 350 years later, it reached a vast region of interstellar gas and dust. This explosion lit up the surrounding material, warming it and causing it to glow in infrared light.

Thanks to NASA’s James Webb Space Telescope, astronomers are now able to observe this glowing cosmic material in unprecedented detail.

The infrared light echoes created by this supernova have revealed intricate structures, like the knots and whorls of wood grain. These observations have allowed scientists to map the interstellar medium in 3D for the very first time.

Interstellar gas and dust details

“We were pretty shocked to see this level of detail,” said Jacob Jencson, principal investigator from Caltech/IPAC in Pasadena.

The telescope revealed layers of interstellar material, resembling the layers of 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 of the Space Telescope Science Institute in Baltimore.

Webb’s infrared imaging is allowing scientists to peer into areas of space that were once completely concealed, uncovering a hidden cosmic landscape.

What are light echoes?

The light echo phenomenon occurs when a star explodes, sending light into the surrounding clumps of interstellar dust. This light then heats up the dust, causing it to glow in an expanding pattern.

Webb’s Near-Infrared Camera (NIRCam) has been crucial in studying these light echoes, revealing their intricate expansion over just a few weeks – a remarkably fast evolution for cosmic phenomena.

The researchers have focused on a particular light echo near the supernova remnant Cassiopeia A. This light echo comes from background material behind Cassiopeia A, not from the material ejected by the star’s explosion.

NASA’s retired Spitzer Space Telescope first observed this phenomenon, but Webb’s exquisite resolution has provided a far clearer view of these cosmic echoes.

Stunning images from Webb

The most striking features in the Webb images are dense, tightly packed sheets of gas and dust. These filaments appear on scales of about 400 astronomical units – less than one-hundredth of a light-year.

“We did not know that the interstellar medium had structures on that small of a scale, let alone that it was sheet-like,” said Josh Peek.

These sheet-like structures might be influenced by interstellar magnetic fields. Webb’s images also showcase areas resembling knots in wood grain, which could represent magnetic “islands” within the interstellar medium’s more uniform magnetic fields.

3D scan of the cosmos

The data collected from Webb are revolutionary. “This is the astronomical equivalent of a medical CT scan,” explained Armin Rest of the Space Telescope Science Institute.

“We have three slices taken at three different times, which will allow us to study the true 3D structure. It will completely change the way we study the interstellar medium.”

These findings will not only enhance our understanding of the space around us, but they could also change how we approach the study of the universe’s most distant and mysterious regions.

Opportunities to study light echoes

In addition to these spectacular images, the team is planning to conduct spectroscopic observations using Webb’s Mid-Infrared Instrument (MIRI).

“We can observe the same patch of dust before, during, and after it’s illuminated by the echo and try to look for any changes in the compositions or states of the molecules,” said Jencson.

Infrared light echoes are rare events that require a unique type of supernova explosion. The upcoming Nancy Grace Roman Space Telescope is expected to provide additional opportunities to study light echoes, potentially offering new insights that Webb can explore in greater detail.

The lasting legacy of Webb

“Even as a star dies, its light endures – echoing across the cosmos. It’s been an extraordinary three years since we launched NASA’s James Webb Space Telescope,” reflected NASA Administrator Bill Nelson.

“Every image, every discovery, shows a portrait not only of the majesty of the universe but the power of the NASA team and the promise of international partnerships.

“What a privilege it has been to oversee this monumental effort, shaped by the tireless dedication of thousands of scientists and engineers around the globe. This latest image beautifully captures the lasting legacy of Webb – a keyhole into the past and a mission that will inspire generations to come.”

Image Credit: NASA, ESA, CSA, STScI, J. Jencson (Caltech/IPAC)

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