27Mar2013

Clues From Kepler’s Supernova Clarifies Cosmic Distances.

Credit: X-ray: NASA/CXC/NCSU/M.Burkey et al; Infrared: NASA/JPL-Caltech

The NASA Chandra X-Ray Observatory has been busy… Busy with a very famous supernova. Discovered in 1604 by Johannes Kepler, this particular type of supernova is interesting.

It has been utilized in determining the expansion rate of the Universe. Through a detailed study, Chandra has taken observations of Kepler’s supernova to a new level, one which has shown it was triggered by an interaction with a white dwarf and red giant star. The findings are important because another study has shown a Type Ia event was the progenitor of the same supernova! 

Conflicting opinions? Not really. We know that the thermonuclear explosion of a white dwarf star is the cause of Type Ia supernovae. Because they ignite with uniform brightness, astronomers are able to use events such as these to aid in measuring cosmic expansion because they act as a constant. However, there are questions about these supernovae events – ones that require an answer. Astronomers need to know if Type Ia supernovae originate from a white dwarf accreting so much matter from a companion star that it causes it to become unstable – or does it happen when two white dwarf stars merge?

“While we can’t speak to all Type Ia supernovas, our evidence points to Kepler being caused by a white dwarf pulling material from a companion star, and not the merger of two white dwarfs,” said the first author of the new Chandra study, Mary Burkey of North Carolina State University (NCSU). “To continue improving distance measurements with these supernovas, it is crucial to understand how they are triggered.”

Kepler’s supernova remnant is important because it one of just a handful of its type known to have occurred in the Milky Way. Because it is relatively close in cosmic terms – and happened on known date – makes it a perfect example.

“Johannes Kepler made such good naked-eye observations in 1604 that we can identify the supernova as Type Ia,” said co-author Stephen Reynolds, also of NCSU. “He would be thrilled that we can use today’s terrific instruments to reveal the hidden secrets of his supernova.”

Now Chandra has given us even more information on Type Ia supernovae by revealing a disk-shaped anomaly at its heart. Researchers are theorizing this X-ray source may have been the result of the supernova detritus and stellar shell material combining before the star exploded. However, they have not ruled out the disk could simply be supernova debris. There is no clear cut answer. They have found evidence the supernova disk contains magnesium – an element not produced by Type Ia supernova events. This points to the giant companion star having produced it.

On the other hand, the disk resembles one also observed by the Spitzer Space Telescope… a dusty band released by stellar winds instead of supernova. The mystery also deepens with the revelation of a dense pocket or iron found at one side of the remnant, but not the other. The authors theorize this lopsided appearance may be a “shadow” in iron – an imprint left by the companion star when it blocked ejected material.

“One remaining challenge is to find the damaged and fast-moving leftovers of the giant star that was pummeled by the explosion at close quarters,” said co-author Kazimierz Borkowski, also of NCSU.

As of now, most astronomers favor the theory that Type Ia supernova are the product of a white dwarf merger – both in the Milky Way and other galaxies as well. Thanks to the latest observations, there is even more conclusive evidence that Type Ia supernova “may have more than one triggering mechanism”. It is entirely possible they have a similar origin, but the researchers aren’t positive that Kepler’s supernova was “typical”.

“We could settle the issue of how normal – or abnormal –the Kepler supernova was if we could discover some light from the supernova explosion that just happened to bounce off some interstellar dust to take a few hundred extra years to get here: a light echo,” said Reynolds. Such light echoes have been found for two other Galactic supernovas in the last millennium.

Original Story Source: Chandra News Release. Submitted by Tammy Plotner for “Dave Reneke’s World Of Space And Astronomy News”.

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