Astronomy/Type Ia Supernovae

For 2012, the Astronomy event will focus on stellar evolution and type Ia supernovae.

Supernovae
A supernova is, in short, the explosion of a star. This term can apply to several different types of explosions, though, and so, like many other astronomical terms, there are classifications. Type Ia supernovae are explosions of white dwarves in binary systems that pull mass off of their partner and accumulate enough pressure for a supernova. Type Ib and Ic supernovae are formed when a large star is stripped of its outer hydrogen layers. The Type I supernovae are generally associated with binary systems. Type II supernovae are explosions of supergiant stars that occur when the star fuses iron in its core. Some Type II supernovae are hypernovae, occuring in hypergiants, even larger and brighter than regular supergiants.

Type Ia
Basically, these supernovae are the explosions of white dwarfs. All type Ia supernovae emit roughly the same amount of energy because they result from the same type of star (a carbon/oxygen white dwarf around 1.4 solar masses), making them a good tool to determine galaxy distances. These supernovae also have very distinctive light curves that fall off quickly and steadily, as compared to the gradual fall-off of Type II supernovae. The spectra is also distinctive, since exploding dwarfs don't have hydrogen absorption lines.

Type Ia supernovae occur because of the Pauli Exclusion Principle, which states that two particles of the same type can't be in the same quantum state (position, velocity, energy level, spin, etc.). Quantum mechanics says that as a white dwarf gains mass and its electrons are squeezed into a smaller and smaller space, they have to move faster to avoid being in the same quantum state as other electrons. As a white dwarf approaches the Chandrasekhar Limit, its electrons must move at nearly the speed of light! Since nothing in the universe can move faster than the speed of light, a white dwarf can't exist above 1.4 solar masses, and instead collapses into a neutron star or a black hole.