Animation of a Cataclysmic Binary (2011)
This video shows an interacting binary star system known as a cataclysmic variable
(CV) or cataclysmic binary. The larger star is a red dwarf, a normal and very common
star somewhat smaller, cooler and fainter than the Sun. It is in orbit around a much
smaller, very dense companion star called a white dwarf. White dwarfs contain as much
material as a star like the Sun, yet they are comparable in size to the planet Earth.
Because the two stars in a CV are so close to each other,
the gravity of the white dwarf distorts the red dwarf into a teardrop shape. Gas at
the point of the teardrop - a region known as the inner Lagrangian (or L1) point -
spills over towards the white dwarf and flows towards it, forming a pancake of gas
called an accretion disc. From here, the gas makes its way to the surface of the
white dwarf. If the white dwarf accumulates too much material too quickly, a nova
explosion happens, emptying the disc. The disc is recreated and the process starts
over. In some cases the white dwarf accumulates so much gas from this disc, though,
that its mass exceeds the so-called Chandrasekhar limit. The white dwarf then becomes
unstable and implodes under its own weight - an event called a type 1a supernova.
Unlike novas, supernovas are final; they cannot reoccur because the white dwarf is
destroyed in the process, turned into either a black hole or a neutron star.
