Why do stars eventually eject their outer layers and become white dwarfs?

Question

My understanding of stellar life cycles is that they eventually run out of core fusion fuel, so they begin fusing fuel in the other layers of the star, causing them to swell into red giants. As they consume their fuel, they eject their outer layers, which form a planetary nebula surrounding the cooler white dwarf. Finally, it cools into a black dwarf.

I don't understand what causes them to lose their mass. Is fusion actually consuming mass, losing it as radiated energy? In that case, does a loss of mass cause a loss of gravity, allowing the material to escape?

Also, are black dwarfs permanent structures, or do they decay further?

Answer 1

You have it right, mostly. As a star like our sun slowly burns its Hydrogen fuel, it gradually grows hotter and hotter. This is because the Helium that is so produced is denser than the lighter Hydrogen, and the more Helium there is, the greater gravity density that can exist in the core, which makes the core hotter and denser, which causes more efficient fusion, making the star grow hotter. Eventually the star grows so hot and so dense in the core that the Helium core "pops" which means the star all of a sudden starts making carbon from Helium, which is an added energy input, which causes the star to semi-explode into a red giant which causes the outer layers to achieve escape velocity and form a planetary nebula, leaving the remainder to slowly cool and contract into a white dwarf, which eventually burns completely out and ultimately assumes galactic ambient temperature which is around 2.6 degrees Kelvin, I believe. Black dwarves are permanent.

Answer 2

Betelgeuse and Antares are the closest crimson great sizeable stars, the two certainly one of that are going to pass off as a center cave in supernovae finally. even nevertheless, they are no longer the closest celeb which could explode as a supernova, IK Pegasi is at a distance of a hundred and fifty mild year the closet celeb which will explode as a supernova. It consists of a great a million.2 image voltaic mass white dwarf purely 19 million miles from an A-type significant sequence celeb. while that stat expands right into a crimson sizeable, it rather is going to push the white dwarf's mass upwards till electron degeneracy can no longer oppose gravity. The celeb will cave in, runaway nuclear reactions start up in the middle, then they eat the full white dwarf which will then explode as a variety 1A supernova. For a supernova to do extreme harm to us, it might could desire to pass off interior 30 mild years, maybe 50 mild years at maximum. Farther away, we'd be bombarded by potential of plenty extra x-rays, gamma rays and cosmic rays than ordinary which will have an result upon the climate. Betelgeuse and Antares will pose no threat to us while they explode, yet they're going to do away with darkness from the sky brighter than an entire moon while they do go supernova.

Answer 3

You've got it right.

Fusion of hdrogen, helium, etc. converts mass into energy; loss of mass reduces pull of gravity; planetary nebulae released because outward pressure of fusion-energy released is greater than mass can contain by gravity; cooling continues, resulting in dark star.

No change likely then unless contact with other mass or energy causes it.

Answer 4

There is no predicted state beyond a Black Dwarf and the Universe is not old enough for the time expected for a star to cool to this point.

Answer 5

i thinkl your crazy