Scientists have discovered that potentially habitable planets exist in an unexpected location.

When astronomers discovered new planets beyond our Solar System, they were quite astonished to find that some of them orbit white dwarf stars. These stars are sometimes referred to as dead stars, as they are remnants of sun-like stars that have reached the end of their life cycle and transformed into small, dense objects roughly the size of Earth after the red giant phase. Considering that the planets orbiting white dwarfs are known to lack atmospheres, they were thought to be lifeless worlds. Consequently, the search for potentially habitable planets has focused on exploring the vicinity of ordinary stars. The authors of a new study published on the preprint server arXiv believe that there may still be planets near a small number of white dwarfs capable of supporting life, according to Universe Today.

Observations of white dwarfs have revealed that some planets orbiting these stars may indeed possess atmospheres. It is possible that these planets were located far from the star, which expanded into a red giant at the end of its life, thus sparing their atmospheres from damage.

Previous studies have indicated that a small percentage of planets orbiting white dwarfs retain their atmospheres. It is also known that such planets can migrate closer to white dwarfs to enter their habitable zones. This is the region of space where conditions allow for the existence of a key component for life – liquid water – on the planet's surface.

However, there is another issue. In the cores of white dwarfs, nuclear fusion does not occur, meaning these stars cannot generate heat over billions of years and instead gradually cool down. This implies that over time, the habitable zone of a white dwarf shrinks.

Thus, any planet within the habitable zone eventually finds itself outside of it and becomes a cold world. This suggests that such planets cannot be potentially habitable. However, the authors of the study hold a different view, at least concerning certain white dwarfs.

Modeling shows that about 6% of white dwarfs slow down their cooling rates. Although nuclear fusion does not take place in a white dwarf's core, processes like radioactive decay and other nuclear interactions still occur. As neutron-rich isotopes move, the interior of the white dwarf shifts, releasing a significant amount of gravitational energy. This continues to heat the star, allowing it to generate warmth.

Scientists have found that some white dwarfs can pause their cooling process for up to 10 billion years. This means that the habitable zone of the star will remain stable during this time.

10 billion years is roughly the lifespan of our Sun, which has about 5.5 billion years left before it becomes a red giant and then a white dwarf.

Researchers believe that such a timeframe is sufficient for life to potentially emerge and evolve on a planet orbiting a white dwarf. Therefore, the search for potentially habitable planets should also include those near white dwarfs that have halted their cooling processes, say the study's authors.