Is it a good idea to search for traces of life on planets near dying stars? New research suggests no: it is unlikely that we will find life near such stars.
Researchers from the University of Washington state this. During their studies, they focused on white dwarfs: the hot cores of dead stars. They also looked at brown dwarfs, or failed stars. Although nuclear reactions no longer take place in both stars and the stars are therefore not nearly as bright as our sun, they can in theory still be clear enough to create a habitable zone: orbit around the star in which it is not too cold, so that water on planets in this zone does not freeze, but is also not too hot, so that water on planets in this zone does not evaporate either.
So far it sounds like a habitable planet around a dying or failed star is possible. But white and brown dwarfs may be a bit clear; they gradually cool down. In concrete terms, this means that the habitable zone is shifting. The star is cooling down, so planets must now be closer to the star so that it is not too cold, but also not too hot.
It follows that a planet that is now in the habitable zone some time ago (when the star gave off more heat) may have been too close to the star, causing all the water on the planet to evaporate. So it is very likely that planets that are now in the habitable zone around a dying or failed star have become unlivable long before they landed in that zone. "These planets that we find today in the livable zone have previously gone through phases that they have sterilized forever," says researcher Barnes. "So even if they are in living sin today, they are dead."
When we observe planets around failed or dying stars, we will therefore have to be critical and not only look at the current location of the planet, but also what it has been dealing with in the past. In many cases it will then appear that planets have an unpredictable history to make life possible.