Power output of red dwarfs turning yellow and blue?

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Summary:

In latter stages of a red dwarf's life it will start to glow yellow and then eventually blue. What happens to the habitable zones of these objects then?

Main Question or Discussion Point

Although the universe is not old enough to experience these yet, but near the end of the lives of red dwarf stars, they will go from red to yellow, to blue eventually. Does this result in additional heat being given off of the surface of those stars? And if so, then does the habitable zone of these stars migrate outwards, and by how much?

The reason I'm asking is because if the habitable zones of red dwarf stars are currently so nearby that it results in tidally locked planets. So once the red dwarfs become yellow and then blue, will their habitable zones migrate out to locations where the planets that might exist in those locations be non-tidally-locked?
 

Answers and Replies

  • #2
stefan r
Science Advisor
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Yes the habitable zone moves outward.

The planets have more time for tidal forces to lock the planet. The rate of slow down varies greatly depending on the composition of the planet. Planets do not start with the same rotation rate.
 
  • #3
stefan r
Science Advisor
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Wikipedia has the equation for time to tidal lock.

The angular momentum that the planet loses will be added to the orbit.

And if so, then does the habitable zone of these stars migrate outwards, and by how much?

This paper gives you details on how much. The range increases with increasing mass. At 0.25 solar mass the final stage is basically like a red giant. Between 0.16 and 0.2 solar mass the stars end with close to solar luminosity. Increases by several hundred over the luminosity at start of the main sequence.

The radius of the habitable zone increases by the square root of luminosity.
 

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