what makes it habitable?
It has been proposed that  dwarfs the surface temperatures of less than 10,000 Kelvins could harbor a habitable zone at a distance of c. 0.005 to 0.02 AU that would last upwards of 3 billion years
White dwarf
It has been proposed that white dwarfs with surface temperatures of less than 10,000 Kelvins could harbor a habitable zone at a distance of c. 0.005 to 0.02 AU that would last upwards of 3 billion years. This is so close that any habitable planets would be tidally locked. 
how many stars r in the milky way It is estimated to contain 100–400 billion stars how can its size be described? It is the second-largest galaxy in the Local Group, it is approximately 890 billion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter, the Milky Way would be approximately the size of the contiguous United States. which celestial bodies can be found in this galaxy? It  contain ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes. what is the first celestial body? It is also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter.
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White dwarf [SEP] Habitability
Another suggested constraint to this idea is the origin of those planets. Leaving aside formation from the accretion disk surrounding the white dwarf, there are two ways a planet could end in a close orbit around stars of this kind: by surviving being engulfed by the star during its red giant phase, and then spiralling inward, or inward migration after the white dwarf has formed. The former case is implausible for low-mass bodies, as they are unlikely to survive being absorbed by their stars. In the latter case, the planets would have to expel so much orbital energy as heat, through tidal interactions with the white dwarf, that they would likely end as uninhabitable embers.