Currently there are two known causes for supernovae. But an exploding star spotted in 2005 defies the understood explanations. The theory of how it ignited could explain something unexpected: Why we have calcium in our bones.
According to the current understanding, there are two types of supernovae. There are the hot, young giants that collapse under their own weight; and old dense white dwarves that detonate in a thermonuclear reaction. However, the supernova SN 2005E doesn't conform to either of these types. When it blew up, it threw off too little material and was in the wrong place for a young star; and the chemical makeup didn't match the dwarf type.
When the supernova was spotted in 2005, it had just begun the process of exploding. This allowed a coalition of scientists from around the world to track its progress and emissions from a number of telescopes.
A new kind of supernova
Led by Hagai Perets, now at the Harvard-Smithsonian Center for Astrophysics, and Avishay Gal-Yam of the Weizmann Institute of Science in Rehovot, Israel, one group thinks the supernova's origins lie in a binary star system. They believe the origin star was a low mass white dwarf stealing hydrogen from its binary partner. This continued until the temperature and pressure was great enough to ignite a thermonuclear explosion, which may have destroyed either, or both, of the stars.
Another group of researchers from Hiroshima University in Japan argue that the original star was large, 8-12 times the size of the sun.
Regardless of whether it was two stars or one, SN 2005E emitted unusually high levels of calcium and titanium, which are produced from helium based nuclear reactions, rather than the usual carbon and oxygen associated with white dwarfs. Now it appears a number of previously-observed supernovae might fit this type too — meaning that astronomers have discovered a helium layer on white dwarfs.
The origin of calcium
If true, these relatively dim explosions might not be very uncommon — and may be responsible for the origins of some very important parts of the galaxy. These supernovae might be the origin of positrons (antielectrons) that cluster at the center of the galaxy. One current theory pegs their origin to "dark matter," but these supernovae emit radioactive titanium, which in turn emits positrons as it decays.
Even more interesting, these supernovae may account for all the calcium on our planet, and in our bodies. Almost all elements heavier than Hydrogen and Helium are created in stars, and if these supernovae are frequent enough, they could account for all the calcium that exists in the universe and ourselves. The researchers calculations show that about half the mass expelled was calcium — so it would only take a couple of these supernovae a century to create the high levels of the element found on Earth.