NASA Telescopes Help Solve Ancient Supernova Mystery

WASHINGTON -- A mystery that began nearly 2,000 years ago, when
Chinese astronomers witnessed what would turn out to be an exploding
star in the sky, has been solved. New infrared observations from
NASA's Spitzer Space Telescope and Wide-field Infrared Survey
Explorer, or WISE, reveal how the first supernova ever recorded
occurred and how its shattered remains ultimately spread out to great distances.

The findings show that the stellar explosion took place in a
hollowed-out cavity, allowing material expelled by the star to travel
much faster and farther than it would have otherwise.

"This supernova remnant got really big, really fast," said Brian J.
Williams, an astronomer at North Carolina State University in
Raleigh. Williams is lead author of a new study detailing the
findings online in the Astrophysical Journal. "It's two to three
times bigger than we would expect for a supernova that was witnessed
exploding nearly 2,000 years ago. Now, we've been able to finally
pinpoint the cause."

A new image of the supernova, known as RCW 86, is online at:


In 185 A.D., Chinese astronomers noted a "guest star" that
mysteriously appeared in the sky and stayed for about 8 months. By
the 1960s, scientists had determined that the mysterious object was
the first documented supernova. Later, they pinpointed RCW 86 as a
supernova remnant located about 8,000 light-years away. But a puzzle
persisted. The star's spherical remains are larger than expected. If
they could be seen in the sky today in infrared light, they'd take up
more space than our full moon.

The solution arrived through new infrared observations made with
Spitzer and WISE, and previous data from NASA's Chandra X-ray
Observatory and the European Space Agency's XMM-Newton Observatory.

The findings reveal that the event is a "Type Ia" supernova, created
by the relatively peaceful death of a star like our sun, which then
shrank into a dense star called a white dwarf. The white dwarf is
thought to have later blown up in a supernova after siphoning matter,
or fuel, from a nearby star.

"A white dwarf is like a smoking cinder from a burnt-out fire,"
Williams said. "If you pour gasoline on it, it will explode."

The observations also show for the first time that a white dwarf can
create a cavity around it before blowing up in a Type Ia event. A
cavity would explain why the remains of RCW 86 are so big. When the
explosion occurred, the ejected material would have traveled
unimpeded by gas and dust and spread out quickly.

Spitzer and WISE allowed the team to measure the temperature of the
dust making up the RCW 86 remnant at about minus 325 degrees
Fahrenheit, or minus 200 degrees Celsius. They then calculated how
much gas must be present within the remnant to heat the dust to those
temperatures. The results point to a low-density environment for much
of the life of the remnant, essentially a cavity.

Scientists initially suspected that RCW 86 was the result of a
core-collapse supernova, the most powerful type of stellar blast.
They had seen hints of a cavity around the remnant, and, at that
time, such cavities were only associated with core-collapse
supernovae. In those events, massive stars blow material away from
them before they blow up, carving out holes around them.

But other evidence argued against a core-collapse supernova. X-ray
data from Chandra and XMM-Newton indicated that the object consisted
of high amounts of iron, a telltale sign of a Type Ia blast. Together
with the infrared observations, a picture of a Type Ia explosion into
a cavity emerged.

"Modern astronomers unveiled one secret of a two-millennia-old cosmic
mystery only to reveal another," said Bill Danchi, Spitzer and WISE
program scientist at NASA Headquarters in Washington. "Now, with
multiple observatories extending our senses in space, we can fully
appreciate the remarkable physics behind this star's death throes,
yet still be as in awe of the cosmos as the ancient astronomers."

For more information about Spitzer, visit:


For more information about WISE, visit:



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