Thursday, May 20, 2010
A calcium rich diet
A nice paper showed up in Nature this week by Perets et al. that details a picture of a new type of supernova, based on observations of a system that went 'pop' in a distant galaxy some 110 million years ago. As the photons from this distant cataclysm showed up on Earth in 2005 it was apparent that this stellar explosion belonged to a new category of 'calcium rich' supernova. Perets et al. argue that a low-mass white dwarf (an old stellar core) in a close binary configuration with another star was stealing helium from its companion, until it could gorge no more and gravity caused a catastrophic thermonuclear reaction. Boom. It's by no means certain that this is precisely what happened. Indeed, another paper in Nature presents an alternative model - but if these offbeat supernova are reasonably common then they could be the culprits behind the decent helping of calcium floating around in not just that distant galaxy, but our own as well.
Calcium, forged in these events and spewed out into interstellar space, eventually ends up incorporated into subsequent generations of stars, and planets. Calcium isn't just good for your bones, it plays a critical role in cellular processes as a signaling mechanism that helps keep enzymes and proteins in check. On the Earth its also a major part of our lithosphere, in carbonate rocks and dissolved in the oceans. Without calcium the carbon-silicate cycle that keeps our terrestrial climate under control over hundreds of thousands of years would not operate since calcium ions help 'scrub' carbon-dioxide from the atmosphere.
So, we probably owe a couple of major and critical pieces of our happy existence to a particular class of greedy little white dwarfs. Why do these guys go pop ? Well, before they overeat they are prevented from collapsing under their own weight by quantum mechanical degeneracy pressure - a wonderful consequence of the Pauli exclusion principle. When this fails to support the dwarf it's all over. Perets et al. argue for a slightly less complete failure, with runaway helium fusion at the dwarf's surface, but that only happens because the stage is set by degeneracy pressure keeping such a massive, dense, object alive.
Quantum mechanics and gravity, enjoy that milkshake.