very interesting my friend so the white dwarf-

very interesting my friend

so the white dwarf- which has a much stronger gravity due to denser mass,feeds off the nearby red giant near the end of its life-

using logic, the red giant has expanded over its lifetime because its no longer fusing just hydrogen or helium but something else higher on the periodic table like oxygen or neon or carbon-or fusing hyrogen or helium in a shell around the core if it doesnt have enough mass to fuse higher in the periodic table in the core- type and location of fusion all depends on the mass .
The higher up on the periodic table the fusing is occurring the hotter the internal temperature required for such fusion and the extra forces resulting from that push back pushes the outer boundaries of the star farther out,thus reducing the density/gravity of the outer parts of the giant,which makes it easier for the more subcompact white dwarf with its greater density/gravity, to feed off the giant-

pairs in which one is a neutron star also does same thing but a white dwarf is not near as dense as neutron star- white dwarfs electron field is still intact whereas the neutron star has stripped all electrons away from the atoms and even merged the protons into the slightly larger neutrons


a more long winded explanation from wikipedia:
This image tracks the life of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years.
Red giants are evolved from main-sequence stars with masses in the range from about 0.3 M☉ to around 8 M☉.[5] When a star initially forms from a collapsing molecular cloud in the interstellar medium, it contains primarily hydrogen and helium, with trace amounts of "metals" (in stellar structure, this simply refers to any element that is not hydrogen or helium i.e. atomic number greater than 2). These elements are all uniformly mixed throughout the star. The star reaches the main sequence when the core reaches a temperature high enough to begin fusing hydrogen (a few million kelvin) and establishes hydrostatic equilibrium. Over its main sequence life, the star slowly converts the hydrogen in the core into helium; its main-sequence life ends when nearly all the hydrogen in the core has been fused. For the Sun, the main-sequence lifetime is approximately 10 billion years. More-massive stars burn disproportionately faster and so have a shorter lifetime than less massive stars.[6]

When the star exhausts the hydrogen fuel in its core, nuclear reactions can no longer continue and so the core begins to contract due to its own gravity. This brings additional hydrogen into a zone where the temperature and pressure are adequate to cause fusion to resume in a shell around the core. The outer layers of the star then expand greatly, thus beginning the red-giant phase of the star's life. As the star expands, the energy produced in the burning shell of the star is spread over a much larger surface area, resulting in a lower surface temperature and a shift in the star's visible light output towards the red – hence it becomes a red giant. At this time, the star is said to be ascending the red-giant branch of the Hertzsprung–Russell (H–R) diagram.[6]


Mira A is an old star, already shedding its outer layers into space.
The evolutionary path the star takes as it moves along the red-giant branch, that ends finally with the complete collapse of the core, depends on the mass of the star . For the Sun and stars of less than about 2 M☉[7] the core will become dense enough that electron degeneracy pressure will prevent it from collapsing further. Once the core is degenerate, it will continue to heat until it reaches a temperature of roughly 108 K, hot enough to begin fusing helium to carbon via the triple-alpha process . Once the degenerate core reaches this temperature, the entire core will begin helium fusion nearly simultaneously in a so-called helium flash. In more-massive stars, the collapsing core will reach 108 K before it is dense enough to be degenerate, so helium fusion will begin much more smoothly, and produce no helium flash.[6] The core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the H–R diagram of many star clusters. Metal-rich helium-fusing stars instead lie on the so-called red clump in the H–R diagram.[8]

An analogous process occurs when the central helium is exhausted and the star collapses once again, causing helium in a shell to begin fusing. At the same time hydrogen may begin fusion in a shell just outside the burning helium shell. This puts the star onto the asymptotic giant branch, a second red-giant phase.[9] The helium fusion results in the build up of a carbon–oxygen core. A star below about 8 M☉ will never start fusion in its degenerate carbon–oxygen core .[7] Instead, at the end of the asymptotic-giant-branch phase the star will eject its outer layers, forming a planetary nebula with the core of the star exposed, ultimately becoming a white dwarf. The ejection of the outer mass and the creation of a planetary nebula finally ends the red-giant phase of the star's evolution.[6] The red-giant phase typically lasts only around a billion years in total for a solar mass star, almost all of which is spent on the red-giant branch. The horizontal-branch and asymptotic-giant-branch phases proceed tens of times faster.
If the star has about 0.2 to 0.5 M☉,[7] it is massive enough to become a red giant but does not have enough mass to initiate the fusion of helium.[5] These "intermediate" stars cool somewhat and increase their luminosity but never achieve the tip of the red-giant branch and helium core flash. When the ascent of the red-giant branch ends they puff off their outer layers much like a post-asymptotic-giant-branch star and then become a white dwarf.




http://blogs.discovermagazine.com/badastronom...XIDE4Tyu1s