Thursday, October 1, 2009

Chapter 8 - Rabbit The White Dwarf - From Blue Giant to Blue Marble


A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron degenerate matter.Because a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth,it is very dense. Their faint luminosity comes from the emission of stored heat.–Wikipedia
If (the white dwarf star) Rabbit blew up in a supernova 4.5 Gya, and the Sun was formed 4.7 Gya, then Rabbit must have been around a lot longer than (predating) the Sun. White dwarf stars are (only) created when a red giant star expels its outer layers of gas (in a planetary nebula), leaving the metal core behind (which becomes the white dwarf). This means that there was a progenitor star to Rabbit and it was a red giant (call it Queen).

But I’m getting ahead of myself! A white dwarf blows up in a supernova when its mass exceeds 1.4 solar masses (1.4x the mass of the Sun) – which is called the Chandrasekhar limit. Usually this is accomplished when a white dwarf “sucks” matter away from a nearby star. This matter (gas, dust) creates a disk around the white dwarf (called an accretion disk) before falling onto the white dwarf. So Rabbit would have been “sucking” matter from the Sun until it got “fat” enough to explode. The disk must have been “wafer thin” . . .


Figure 20 Artist's conception of a white dwarf star accreting hydrogen from a larger companion
(http://en.wikipedia.org/wiki/File:Making_a_Nova.jpg)

Some scientists believe that the Rabbit supernova is what “sparked” the creation of the Solar System. If the supernova occurred 4.5 Gya, the Moon rocks were already formed by then thus the supernova could not have created the Solar System. Even if the supernova occurred 4.7 Gya, that doesn’t leave much time for the planets to accrete (and the supernova “stuff” to settle out). I don’t believe this is the way it happened. The Rabbit supernova did not create the Solar System – the creation of the Solar System triggered the Rabbit supernova!

That will take some explaining, so lets tell the whole story.


A previous conundrum says that supernovas do a poor job of creating boron-5 and beryllium-4, but the Earth has tremendous amounts of the stuff. So where did it come from?

Supernovas are not the only mechanism for creating “star stuff” - there is another process that can create new elements. This process is called a nova (instead of supernova). A white dwarf star (convenient!) accretes gas/dust/star stuff on its surface from a companion star (or cloud) and this material undergoes fusion – which creates new material that gets thrown into space in a bright “flash” (the nova). Novas can create all sorts of material – each flash could be a different element or compound. Usually only the lightest (least mass) material is created – and beryllium-4 and boron-5 fit that description.

Novas can create carbon and oxygen and sulfur (and neon and other things), and these atoms can combine with others to make molecules like water and carbon dioxide. Hmm, Co2 and sulfur describe Venus’s atmosphere while water and oxygen (and nitrogen!) sound a whole lot like the Earth’s atmosphere. So how do you get lighter elements in the inner Solar System (where you would expect heavier ones)? Can you say No-va (just don’t say it in Spanish)?



Proposal 6
The lighter mass elements that are found in the inner Solar System came from Rabbit’s novas.


But a white dwarf that novas on a regular basis gets rid of “extra” mass – which means no build-up of mass to a supernova. Oh crap. But even if it could go supernova, it would probably destroy the whole Solar System. How do you “moderate” a supernova explosion so that most of the Solar System is spared? And how do you trigger one in a star that already novas?

Let’s examine the roots of Rabbit and maybe we can formulate a better hypothesis.

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