Sky & Telescope - May 2024 - 13

Astronomers use supernova remnants to learn about the lives and deaths of stars that
went kablooey.
W
hen dying stars blow themselves to smithereens,
they leave behind a mess. These messes,
called supernova remnants, are marvelous
medleys of material, sometimes replete with intricate filaments
or lit from within by intense radiation.
Supernova remnants are where we see the link between
stellar and galactic evolution unfold. Dumped into surrounding
gas, the energy of a supernova explosion helps
regulate star formation. The stellar guts, meanwhile,
spread out over dozens of light-years in thousands of years.
The debris seeds space with many of the universe's heavy
elements and changes the chemical makeup and development
of subsequent generations of stars and planets.
Each year, astronomers catch hundreds of supernovae
detonating in distant galaxies. But although we can learn
a lot from watching how the explosions brighten and fade,
ultimately they're just bright dots in our images.
So to better understand how stars detonate, astronomers
dissect stars' remains. Supernova remnants have the
potential to reveal everything from the mass and composition
of the now-gone star to the mechanisms behind the
explosion and whether the star threw off a lot of material
before it died. They are the ultimate autopsy record.
(continued on page 16)
CASSIOPEIA A Lying some 11,000 light-years from Earth, the
supernova remnant Cas A spans about 10 light-years. This image is a
mid-infrared composite using data from the James Webb Space Telescope.
The orange and red colors mark where the explosion's blast
wave and outermost ejecta are ramming into dusty material surrounding
the dead star. The knotty, pinkish-white material is stellar debris,
heated by the shock wave that's reflecting back from the collision
between ejecta and circumstellar gas.
MYSTERY " BUBBLES " Box: The round, puncture-like features
along the curve of the green arc puzzled astronomers when JWST
revealed them. Subsequent study now indicates that the features (and
the " green monster " they pockmark) are not inside the remnant at all
but rather lie just outside it in the foreground. The holes appear to be
real holes, created when knots of ejecta punched like shotgun spray
through the dusty gas surrounding the supernova, Dan Milisavljevic
(Purdue University) announced at a press conference in January.
PRISTINE EJECTA By subtracting out emission from the remnant's
shell and surrounding dusty gas, Milisavljevic and his colleagues revealed
the infrared glow of supernova debris deep inside the remnant.
This debris is as of yet unaltered by shock waves reflecting inward
from the collision between ejecta and circumstellar material. Preliminary
study of the debris indicates that very little radioactive nickel
remained close to the explosion's center - confirming that heavy
elements in the star's core were somehow ejected out ahead of the
lighter elements in the overlying layers. To achieve that, the explosion
must have been messy.
sk yand tele scope .o r g * MAY 2024 13
CASSIOPEIA A: NASA / ESA / CSA / DANNY MILISAVLJEVIC (PURDUE UNIVERSITY),
TEA TEMIM (PRINCETON UNIVERSITY), ILSE DE LOOZE (UNIVERSITY OF GENT);
CASSIOPEIA A INTERIOR: D. MILISAVLJEVIC ET AL. 2024
http://skyandtelescoper.org
Sky & Telescope - May 2024

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