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| Danny Milisavljevic’s research on the James Webb Space Telescope led to his new detailed image of stellar remnant Cassiopeia A in which infrared light is translated into visible-light wavelengths. Credit: NASA image |
To gaze at the stars is human. To be able to see them in three-dimensional
detail is very nearly divine.
Divine vision is what the James Webb Space Telescope has granted Earthbound
scientists in a new near-infrared, detailed image of Cassiopeia A (Cas A), a
stellar remnant—the clouds of gas, dust and other material left behind when
a star dies. Danny Milisavljevic, assistant professor of physics and
astronomy in Purdue University's College of Science, studies supernova
remnants and leads a year one research team on the JWST examining Cas A.
"I have spent 17 years studying stars and their titanic explosions. I've
used dozens of telescopes—both ground- and space-based—covering the
electromagnetic spectrum from gamma rays to radio wavelengths,"
Milisavljevic said. "And yet, I was still unprepared for the data that Webb
has provided. I am awestruck by their quality and beauty."
Cassiopeia A is the youngest known remnant from an exploding, massive star
in our galaxy, which makes it a unique opportunity to learn more about how
such supernovae occur. The light from its explosion first arrived at Earth
340 years ago.
"Cas A represents our best opportunity to look at the debris field of an
exploded star and run a kind of stellar autopsy to understand what type of
star was there beforehand and how that star exploded," Milisavljevic said.
Supernovae like the one that formed Cas A are crucial for life. Stars create
a variety of elements, and subsequent supernovae create additional
elements—everything from the calcium in our bones to the iron in our
blood—and spread them across interstellar space, seeding new generations of
stars and planets.
"By understanding the process of exploding stars, we are reading our own
origin story," Milisavljevic said.
Looking with new eyes
Located about 11,000 light-years away, the remnant is in the section of the
sky considered to be of the constellation Cassiopeia. An arrangement of five
bright stars in a "W," Cas A is invisible to human eyes from Earth but
occupies the space that appears to be off to the right of the last stroke of
the W.
For decades, scientists have studied Cas A. Examining the structure using
different wavelengths gives astronomers new insights into star anatomy, the
same way infrared cameras give humans different information than cameras
that see only in the visible light spectrum.
The new image collected by JWST's golden honeycomb of 18 mirrors shows
incredible detail. In it, mid-infrared light has been translated into
visible light, allowing scientists to analyze details and structures. Great
curtains of material, shaded red and orange, represent where the star's
material is crashing into circumstellar gas and dust. Among those rosy
swaths, bursts of pink show where the star's composite elements, including
oxygen, argon and neon, are shining.
For the researchers, one of the most puzzling elements of the image is the
large green loop on the image's right side.
"We've nicknamed it the Green Monster, in honor of Fenway Park in Boston,"
Milisavljevic said. "If you look closely, you'll notice that it's pockmarked
with what look like little bubbles. The shape and complexity are unexpected
and challenging to understand."
Higher resolution images, in more wavelengths especially the infrared, give
astronomers a clearer look at the intricacies of the structure. Like picking
up binoculars to help resolve the colors and patterns on a bird's wing, the
more detail scientists have, the more information they can infer and
analyze.
"Compared to previous infrared images, we see incredible detail that we
haven't been able to access before," said Tea Temim, a program
co-investigator from Princeton University.
Dust to dust
Counterintuitively, some of the most exciting matter in the picture may seem
the most prosaic: dust. While the substance is irritating to housekeepers,
it is intriguing to astronomers.
Massive quantities of dust suffuse even very young galaxies in the early
universe. It's difficult to explain the origins of this dust without
crediting supernovae, which spew large quantities of heavy elements—the
building blocks of dust—across space.
But supernovae can also destroy dust, and it's unclear how much survives the
trip to interstellar space. By studying Cas A with JWST, astronomers hope to
gain a better understanding of its dust content, which can help inform our
understanding of where the building blocks of planets—and ourselves—are
created.
"In Cas A, we can spatially resolve regions that have different gas
compositions and look at what types of dust were formed in those regions,"
Temim said.
Carl Sagan famously assured humanity that we are made of "star stuff."
Milisavljevic's team and JWST's observations are helping scientist
understand that process.
"Webb is an incredible achievement," Milisavljevic said. "I feel fortunate
to be among the first scientists to test its unrivaled power to explore the
universe. I am going to spend the rest of my career trying to understand
what's in this data set."
Source: Purdue University
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Space & Astrophysics