17Sep2012

Kepler’s Supernova – Super Powerful?

Credits: X-ray: NASA/CXC/SAO/D.Patnaude, Optical: DSS

When it comes to cataclysmic cosmic events, there are very few more powerful than a Type Ia supernova…one of nature’s most powerful events.

Indeed, there very few more powerful instruments to study them with than the Chandra X-Ray Observatory. In this new image, Chandra was called upon to study a very famous mystery – Kepler’s Supernova. The data comes from more than eight days of observing time and the x-rays are shown in five colors from lower to higher energies: red, yellow, green, blue, and purple. The information was then combined with optical images from the Digitized Sky Survey to provide field stars.

Does this new image show a powerful Type Ia supernova – one that’s just a bit stronger than considered “normal”? Chandra and another optical telescope has been down this route before when studying another such remnant in the Large Magellanic Cloud. While it is more distant the Kepler’s Supernova and more difficult to study, the two telescope made use of their observations through a phenomenon known as light echoes – and Kepler’s remnant is very different. Its debris field is being molded by its surroundings. In most cases, Type Ia supernova remnants are distributed very evenly, but the Kepler remnant is oddly shaped with an illuminated arc of X-ray emission along its northern flank. This means the expanding debris cloud from the stellar explosion is encountering gas and dust surrounding the expired star.

Astronomers have tried for many years to explain exactly what happened to create the Kepler supernova remnant and NASA’s Chandra X-ray Observatory is helping to solve the riddle. According to the new data, this supernova event may have happened at a greater distance than previously suggested and was much more powerful. It is the result of a white dwarf star gaining mass – either by pulling gas from a companion star or merging with another white dwarf. When this occurs, it becomes unstable and annihilates itself via a thermonuclear explosion. However, the bright arc is a complete mystery.

“The bright X-ray arc can be explained in two ways. In one model, the pre-supernova star and its companion were moving through the interstellar gas and losing mass at a significant rate via a wind, creating a bow shock wave similar to that of a boat moving through water.” says the Chandra team. “Another possibility is that the X-ray arc is caused by debris from the supernova expanding into an interstellar cloud of gradually increasing density.”

However, this explanation produces even more questions. The wind and bow shock model described above means the Kepler supernova remnant should be situated at a distance of more than 23,000 light years. In the second scenario, the gas housing the expanding remnant has a higher density than average, and the distance of the remnant from Earth is between about 16,000 and 20,000 light years. No matter which theory you choose, both give greater distances than the 13,00 light years as previously thought.

To further deepen the mystery, the X-ray spectrum shows a large amount of iron – an indicator the explosion was more powerful than an average Type Ia supernova. What could have caused this? Astronomers speculate that a small cavity must have cleared around the star before it exploded. If this is true, the hollow would have had to have been less than a tenth of the current remnant’s size and caused by a fast, dense outflow from the progenitor star’s surface before it exploded.

Don’t you wonder what Kepler would have thought had he known as much in 1604 as we do now?!

Original Story Source: NASA / Chandra News Release.

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