This is the first map of radioactivity in a
supernova remnant, the blown-out bits and pieces of a massive star that
exploded. The blue color shows radioactive material mapped in high-energy X-rays
using NuSTAR.
Image Credit:
NASA/JPL-Caltech/CXC/SAO
Feature Link:
NuSTAR is complementing previous observations of
the Cassiopeia A supernova remnant (red and green) by providing the first maps
of radioactive material forged in the fiery explosion (blue).
Image Credit:
NASA/JPL-Caltech/CXC/SAO
Feature Link:
These illustrations show the progression of a
supernova blast. A massive star (left), which has created elements as heavy as
iron in its interior, blows up in a tremendous explosion (middle), scattering
its outer layers in a structure called a supernova remnant (right).
Image Credit:
NASA/CXC/SAO/JPL-Caltech
Feature Link:
One of the biggest mysteries in astronomy, how stars blow up in supernova
explosions, finally is being unraveled with the help of NASA's Nuclear
Spectroscopic Telescope Array (NuSTAR).
The high-energy X-ray observatory has created the first map of radioactive
material in a supernova remnant. The results, from a remnant named Cassiopeia A
(Cas A), reveal how shock waves likely rip apart massive dying stars.
"Stars are spherical balls of gas, and so you might think that when they end
their lives and explode, that explosion would look like a uniform ball expanding
out with great power," said Fiona Harrison, the principal investigator of NuSTAR
at the California Institute of Technology (Caltech) in Pasadena. "Our new
results show how the explosion's heart, or engine, is distorted, possibly
because the inner regions literally slosh around before detonating."
Harrison is a co-author of a paper about the results appearing in the Feb. 20
issue of Nature.
Cas A was created when a massive star blew up as a supernova, leaving a dense
stellar corpse and its ejected remains. The light from the explosion reached
Earth a few hundred years ago, so we are seeing the stellar remnant when it was
fresh and young.
Supernovas seed the universe with many elements, including the gold in
jewelry, the calcium in bones and the iron in blood. While small stars like our
sun die less violent deaths, stars at least eight times as massive as our sun
blow up in supernova explosions. The high temperatures and particles created in
the blast fuse light elements together to create heavier elements.
NuSTAR is the first telescope capable of producing maps of radioactive
elements in supernova remnants. In this case, the element is titanium-44, which
has an unstable nucleus produced at the heart of the exploding star.
The NuSTAR map of Cas A shows the titanium concentrated in clumps at the
remnant's center and points to a possible solution to the mystery of how the
star met its demise. When researchers simulate supernova blasts with computers,
as a massive star dies and collapses, the main shock wave often stalls out and
the star fails to shatter.
The latest findings strongly suggest the exploding star literally sloshed
around, re-energizing the stalled shock wave and allowing the star to finally
blast off its outer layers.
"With NuSTAR we have a new forensic tool to investigate the explosion," said
the paper's lead author, Brian Grefenstette of Caltech. "Previously, it was hard
to interpret what was going on in Cas A because the material that we could see
only glows in X-rays when it's heated up. Now that we can see the radioactive
material, which glows in X-rays no matter what, we are getting a more complete
picture of what was going on at the core of the explosion."
The NuSTAR map also casts doubt on other models of supernova explosions, in
which the star is rapidly rotating just before it dies and launches narrow
streams of gas that drive the stellar blast. Though imprints of jets have been
seen before around Cas A, it was not known if they were triggering the
explosion. NuSTAR did not see the titanium, essentially the radioactive ash from
the explosion, in narrow regions matching the jets, so the jets were not the
explosive trigger.
"This is why we built NuSTAR," said Paul Hertz, director of NASA's
astrophysics division in Washington. "To discover things we never knew – and did
not expect – about the high-energy universe."
The researchers will continue to investigate the case of Cas A's dramatic
explosion. Centuries after its death marked our skies, this supernova remnant
continues to perplex.
For more information about NuSTAR and images,
visit: http://www.nasa.gov/nustar
NASA
Guillermo Gonzalo Sánchez Achutegui
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