Superwind phase in stellar evolution

In summary, during the superwind phase, there is a very rapid mass loss in stars due to the envelope attaining positive binding energy. This is caused by the formation of molecules and dust during the AGB phase, which trap outgoing flux and drive a strong wind. This mechanism is not fully understood, but it is believed to be a consequence of the star pulsating and the radiation pressure overcoming gravity.
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why is there very rapid mass loss in the superwind phase. my notes simply say "because the envelope attains positive binding energy".

Firstly, how can binding energy be positive by definition?!

Secondly, I am not entirely sure what the lecturer is talking about? what makes the envelope "attain positive binding energy" in the first place? Can't find anything relavent in Carroll and Ostlie:(

thanks in advance:)
 
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  • #2
bump this one too:)
 
  • #3
I'm not sure this mechanism is fully known, however during the AGB phase we observe that some stars begin to pulsate (Mira variables). The systematic compression and expansion causes material to "bunch up" making the formation of molecules (and dust etc.) easier. These trap the outgoing flux and essentially drive a strong wind.
 
  • #4
vertices said:
why is there very rapid mass loss in the superwind phase. my notes simply say "because the envelope attains positive binding energy".
thanks in advance:)

I think it just means that the bound system becomes energetically unfavourable in favour of the unbound? That is to say, the envelope would prefer to be ejected..
 
  • #5
so the mass loss is simply a consequence of the star pulsating.

thanks again astrorob.
 
  • #6
Mass loss is due to radiation pressure (outward) overcoming gravitation (inward).

In very massive stars, the gravity at the surface is weak and the radiation strong, so the matter gets blown away.

As astrorob says, in AGB stars molecules form as the star pulsates. This is due to the dredge-up of carbon and/or oxygen from inside the star. The molecules form into grains which are easily blown outwards by the stellar radiation.
 

1. What is a superwind phase in stellar evolution?

A superwind phase in stellar evolution refers to a period in the life of a massive star where it experiences a rapid loss of mass due to strong stellar winds. These winds are caused by the intense radiation and high temperatures of the star, which push out and carry away its outer layers.

2. How long does a superwind phase last?

The duration of a superwind phase can vary depending on the mass and type of star, but it typically lasts for a few hundred thousand to a few million years. This is a relatively short period in the overall lifespan of a star, which can last for billions of years.

3. What triggers a superwind phase?

A superwind phase is triggered when a massive star runs out of fuel for nuclear fusion in its core. As the core collapses under its own gravity, the outer layers of the star expand and cool, leading to the formation of strong stellar winds.

4. What are the effects of a superwind phase on a star?

The intense mass loss during a superwind phase can significantly alter the structure and evolution of a star. It can cause the star to lose a significant amount of its mass, which can affect its brightness, temperature, and lifespan. The ejected material can also enrich the surrounding interstellar medium with heavy elements.

5. Can we observe superwind phases in other galaxies?

Yes, superwind phases have been observed in other galaxies through various techniques, including spectroscopy and imaging. These observations have provided valuable insights into the evolution of massive stars and their role in shaping galactic ecosystems.

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