December 10, 2013 – 2,000 Year Old Mystery of Deep Space Solved: 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 observations by astronomers 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. “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 supernova is a star that explodes catastrophically owing to either instabilities following the exhaustion of its nuclear fuel or gravitational collapse following the accretion (the process of growth or increase) of matter from an orbiting companion star, becoming for a few days up to one hundred million times brighter than the sun. The expanding shell of debris (the supernova remnant) creates a nebula that radiates radio waves, X-rays, and light, for hundreds or thousands of years.
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” (pictured above) 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, they’d take up more space than our full moon.
The solution arrived through new observations made with special telescopes. The findings reveal that the event is a “Type Ia” supernova (the explosion of a carbon-oxygen white dwarf), 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.
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.
However, the high amounts of iron present are the telltale sign of a Type Ia blast. Together with infrared observations; the existence of a Type Ia explosion emerged.
Modern astronomer’s unveiled one secret of a 2,000 year old cosmic mystery only to reveal another. 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. Note: originally published Nov. 11, 2011.
The Master of Disaster