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infrared image from NASA's Spitzer Space Telescope shows N103B -- all
that remains from a supernova that exploded a millennium ago in the
Large Magellanic Cloud, a satellite galaxy 160,000 light-years away from
our own Milky Way.Image Credit: NASA/JPL-Caltech/Goddard.Full image and caption
are often thought of as the tremendous explosions that mark the ends of
massive stars' lives. While this is true, not all supernovas occur in
this fashion. A common supernova class, called Type Ia, involves the
detonation of white dwarfs -- small, dense stars that are already dead.
New results from NASA's Spitzer Space Telescope have revealed a rare
example of Type Ia explosion, in which a dead star "fed" off an aging
star like a cosmic zombie, triggering a blast. The results help
researchers piece together how these powerful and diverse events occur.
"It's kind of like being a detective," said Brian Williams of NASA's
Goddard Space Flight Center in Greenbelt, Maryland, lead author of a
study submitted to the Astrophysical Journal. "We look for clues in the
remains to try to figure out what happened, even though we weren't there
to see it."
Supernovas are essential factories in the cosmos, churning out heavy
metals, including the iron contained in our blood. Type Ia supernovas
tend to blow up in consistent ways, and thus have been used for decades
to help scientists study the size and expansion of our universe.
Researchers say that these events occur when white dwarfs -- the
burnt-out corpses of stars like our sun -- explode.
Evidence has been mounting over the past 10 years that the explosions
are triggered when two orbiting white dwarfs collide -- with one
notable exception. Kepler's supernova, named after the astronomer
Johannes Kepler, who was among those who witnessed it in 1604, is
thought to have been preceded by just one white dwarf and an elderly,
companion star called a red giant. Scientists know this because the
remnant sits in a pool of gas and dust shed by the aging star.
Spitzer's new observations now find a second case of a supernova
remnant resembling Kepler's. Called N103B, the roughly 1,000 year-old
supernova remnant lies 160,000 light-years away in the Large Magellanic
Cloud, a small galaxy near our Milky Way.
"It's like Kepler's older cousin," said Williams. He explained that
N103B, though somewhat older than Kepler's supernova remnant, also lies
in a cloud of gas and dust thought to have been blown off by an older
companion star. "The region around the remnant is extraordinarily
dense," he said. Unlike Kepler's supernova remnant, no historical
sightings of the explosion that created N103B are recorded.
Both the Kepler and N103B explosions are thought to have unfolded as
follows: an aging star orbits its companion -- a white dwarf. As the
aging star molts, which is typical for older stars, some of the shed
material falls onto the white dwarf. This causes the white dwarf to
build up in mass, become unstable and explode.
According to the researchers, this scenario may be rare. While the
pairing of white dwarfs and red giants was thought to underlie virtually
all Type Ia supernovas as recently as a decade ago, scientists now
think that collisions between two white dwarfs are the most common
cause. The new Spitzer research highlights the complexity of these
tremendous explosions and the variety of their triggers. The case of
what makes a dead star rupture is still very much an unsolved mystery.
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at the Infrared Science Archive
housed at the Infrared Processing and Analysis Center at Caltech.
Caltech manages JPL for NASA.