What will happen when Alpha Centauri dies?

Because Alpha Centauri is also a star nearly identical in type and age to the Sun, it will evolve into a red giant at about the same time the Sun does. When that happens, we will have far more to worry about from our sun's expansion than anything that Alpha Centauri can do to us.

The lumininosity of Alpha Centauri as a red giant star will increase over 2000 times, and its magnitude as a star in the sky will be about -7.0. It will be brighter than Venus, and a deep crimson red like Betelgeuse and Antares.

Aside from this it will have no affect upon the earth. Once it 'dies' and sheds its outer layers as a planetary nebula, this material will come our way at a speed of 10-20 kilometers/sec and get here within 100,000 years or so and produce a new kind of faint background glow perhaps as bright as the zodiacal light we now see from dust inside our solar system. However, our own sun will also be a red giant star about the same time so we may not have an earth upon which to watch all of this happen in the first place!!