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<\/a><\/figure>The inside of a star turned on itself before it spectacularly exploded, according to a new study from NASA\u2019s Chandra X-ray Observatory. Today, this shattered star, known as the Cassiopeia A supernova remnant, is one of the best-known, well-studied objects in the sky.<\/p>\n
Over three hundred years ago, however, it was a giant star on the brink of self-destruction. The new Chandra study reveals that just hours before it exploded, the star\u2019s interior violently rearranged itself. This last-minute shuffling of its stellar belly has profound implications for understanding how massive stars explode and how their remains behave afterwards.<\/p>\n
Cassiopeia A (Cas A for short) was one of the first objects the telescope looked at after its launch in 1999, and astronomers have repeatedly returned to observe it.<\/p>\n
\u201cIt seems like each time we closely look at Chandra data of Cas A, we learn something new and exciting,\u201d said Toshiki Sato of Meiji University in Japan who led the study. \u201cNow we\u2019ve taken that invaluable X-ray data, combined it with powerful computer models, and found something extraordinary.\u201d<\/p>\n
As massive stars age, increasingly heavy elements form in their interiors by nuclear reactions, creating onion-like layers of different elements. Their outer layer is mostly made of hydrogen, followed by layers of helium, carbon and progressively heavier elements \u2013 extending all the way down to the center of the star.\u00a0<\/p>\n
Once iron starts forming in the core of the star, the game changes. As soon as the iron core grows beyond a certain mass (about 1.4 times the mass of the Sun), it can no longer support its own weight and collapses. The outer part of the star falls onto the collapsing core, and rebounds as a core-collapse supernova.<\/p>\n
The new research with Chandra data reveals a change that happened deep within the star at the very last moments of its life. After more than a million years, Cas A underwent major changes in its final hours before exploding.<\/p>\n
\u201cOur research shows that just before the star in Cas A collapsed, part of an inner layer with large amounts of silicon traveled outwards and broke into a neighboring layer with lots of neon,\u201d said co-author Kai Matsunaga of Kyoto University in Japan. \u201cThis is a violent event where the barrier between these two layers disappears.\u201d<\/p>\n
This upheaval not only caused material rich in silicon to travel outwards; it also forced material rich in neon to travel inwards. The team found clear traces of these outward silicon flows and inward neon flows in the remains of Cas A\u2019s supernova remnant. Small regions rich in silicon but poor in neon are located near regions rich in neon and poor in silicon.\u00a0<\/p>\n
The survival of these regions not only provides critical evidence for the star\u2019s upheaval, but also shows that complete mixing of the silicon and neon with other elements did not occur immediately before or after the explosion. This lack of mixing is predicted by detailed computer models of massive stars near the ends of their lives.<\/p>\n
There are several significant implications for this inner turmoil inside of the doomed star. First, it may directly explain the lopsided rather than symmetrical shape of the Cas A remnant in three dimensions. Second, a lopsided explosion and debris field may have given a powerful kick to the remaining core of the star, now a neutron star, explaining the high observed speed of this object.<\/p>\n
Finally, the strong turbulent flows created by the star\u2019s internal changes may have promoted the development of the supernova blast wave, facilitating the star\u2019s explosion.<\/p>\n
\u201cPerhaps the most important effect of this change in the star\u2019s structure is that it may have helped trigger the explosion itself,\u201d said co-author\ufeff Hiroyuki Uchida, also of Kyoto University. \u201cSuch final internal activity of a star may change its fate\u2014whether it will shine as a supernova or not.\u201d<\/p>\n
These results have been published in the latest issue of The Astrophysical Journal and are available online<\/a>.<\/p>\n To learn more about Chandra, visit:<\/p>\n