Article: UWM astronomer's discovery: Like a diamond in the sky
As a star ages, it uses up the hydrogen fuel in its core, converting it to helium. When it does, the core implodes and the shock wave blows the outer layers out into space, forming a planetary nebula. The imploding core puts the helium under pressure, and it starts to burn, making carbon among other things. A smaller star, like own, will stop here.
The core becomes the "white dwarf." Its surface is very hot ("white hot"). It is no longer "burning" any fuel. It is cooling off.
This object has to be very old, to have had time enough to become as cool as it is now. However, the astronomers did not make an estimate as to its age.