Animation of a Cataclysmic Binary
his 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.
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