Telescopes help solve ancient supernova mystery

Oct 24, 2011
This image combines data from four different space telescopes to create a multi-wavelength view of all that remains of the oldest documented example of a supernova, called RCW 86. Image credit: NASA/ESA/JPL-Caltech/UCLA/CXC/SAO

( -- 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 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 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 . "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."

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 made with Spitzer and WISE, and previous data from NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory.

Infrared images from NASA's Spitzer Space Telescope and Wide-field Infrared Survey Explorer (WISE) are combined in this image of RCW 86, the dusty remains of the oldest documented example of an exploding star, or supernova. Image credit: NASA/JPL-Caltech/UCLA

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 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."

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User comments : 8

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5 / 5 (2) Oct 24, 2011
This was a very cool article. I think we could learn a lot from looking back and RE-examanazing the recorded history of astronomy.
3.7 / 5 (3) Oct 24, 2011
OR it could be the Star-ship Enterprise in one of its ventures back in time and in orbit around the earth.
3 / 5 (4) Oct 24, 2011
Since most space is not empty with all that gas and dust, space travel at near light speeds is not possible--unless done in one of these cavities--any space craft would explode when hitting any of these particles when traveling at such velocities. This is one reason why the Universe could be full of intelligent life without any of them having turned up on our front door (Fermi's paradox).
1 / 5 (2) Oct 24, 2011
Beautiful photos - the universe is astonishingly beautiful, as well as somewhat frightening.
1 / 5 (3) Oct 24, 2011
what this article alludes to is that if our current scientific world wide civilization is able to maintain current multi frequency resolution or better astronomy recordings continually for the next 500 years----we will learn an immense amount of information that we could not possibly fathom.

we have JUST entered the age of a new ability of recording----an age where because of digital ability to record lots of data, and then organize and compare the data ---a task even more computationally demanding than merely collecting and storing the data....that we will have a basis for a scale of comparisons of historical empirical recording over a period of human generational scale time ....that has never existed for all of humanities existence.

this is a complex concept , i only wish i was a better writer. but this overlying concept alluded to by this article is truly beautiful. a conceptual butterfly
not rated yet Oct 25, 2011
"The white dwarf is thought to have later blown up in a supernova after siphoning matter, or fuel, from a nearby star."
So we need to add a nearby star, has this been observed or just inferred to get this theory working?

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

"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."

So the necessity of a shell for the theory to work is proof the shells existence? the authors must have failed "assumption hiding 101"
1 / 5 (1) Oct 25, 2011
"A white dwarf is like a smoking cinder from a burnt-out fire," Williams said. "If you pour gasoline on it, it will explode."

Gasoline requires oxigen and pressure to explode. I think it would not explode when throwning it to a white dwarf
not rated yet Oct 25, 2011
The cavity is directly observable, in the history of the gas from the supernova. If there were no cavity, it would be much hotter from the shock waves.

Also, the model of type Ia supernovas has evolved a lot in the last few years. At first, they were just another type of supernova (or subtype to be precise). Now the model requires two stars and two end of life transitions before the final explosion. So over a period of millions of years you could have three supernova events, the final one being a type Ia supernova.

First you have a star which goes through a red giant phase, gets rid of its outer layers (possibly picked up by the companion) and the core remains as a white dwarf. Think Sirius A and B. The white dwarf gains mass from its companion especially if the companion also becomes a red giant. (Sirius A hasn't reached this point yet.) When the white dwarf gains enough mass, boom!