New type of supernovae? Supernova 2005cz (with arrow) suddenly appeared inside the host galaxy NGC 4589.
Credit: Subaru Telescope/NAOJ
PARIS: A new type of exploding star that spews huge quantities of calcium and defies the two known categories of supernovae has been discovered.
Only a handful of these novel star bursts have been spotted over the last few years, but they could explain the abundance of calcium observed in galaxies like our own Milky Way, according to an international group of astronomers who announced the discovery in the British journal, Nature.
The new supernova types might even account for the calcium present in our bones, and in all life on Earth, the researchers added.
Two classes were known
Until now, supernovae - the most energy-intense and brilliant events visible in the universe - have been grouped into two classes.
Type Ia are thought to arise when the gravity of a burnt-out rump star called a white dwarf draws off enough material from a similar star nearby - a process known as accretion - to become unstable.
At a critical tipping point, the star's ultra-dense core of carbon and oxygen ignites into a shattering thermonuclear blast.
Light curves generated by Type Ia supernovae are so regular and predictable that they are used as cosmic benchmarks to measure the speed with which the universe expands.
Stellar destruction
The other known path to stellar destruction involves the gravitational and catastrophic collapse of a hot, massive star's inner core.
When these stars - dubbed Type II, or Type Ib or Ic - become supernovae, they give birth to neutron stars or black holes.
But as to tools for peering into the heavens become more powerful, astronomers have come across supernovae that do not fit neatly into either category.
Unknown physical mechanisms?
The first paper, by Koji Kawabata of Hiroshima University in Japan and colleagues, focuses on Supernova 2005cz, which was observed for six months its cataclysmic explosion. In the second paper, lead author Hagai Perets of the Harvard-Smithsonian Centre for Astrophysics in Boston and colleagues focus on Supernova 2005E, in which the team also found a strong calcium signature.
Both supernovae were generated by a low-mass, helium-rich white dwarf instead of the more common hydrogen-rich white dwarf.
"We're discovering weird ones that may represent different physical mechanisms compared with the two well-known types, or may just be variations on the standard themes," said Alex Filippenko, a professor at the University of California at Berkeley and co-author of one of the studies.
