White dwarfs, bodies of stars similar to the Sun, are known to host planets despite a particularly violent transition phase. However, the nature of these objects renders the most commonly used exoplanet detection techniques ineffective. So how do you find them? A team of astronomers suggests relying on the James Webb Telescope (JWT).
Planets around white dwarfs
Of the more than 5,000 exoplanets identified to date, most evolve around Sun-like stars. This can be explained by several points. First of all, earthly life is the only example of life we know of. In the context of extraterrestrial research, we therefore tend to focus on systems comparable to our own. Then sun stars are also very common. Finally, although small red dwarf stars are the most common in our galaxy, they are much fainter, making it not impossible, but more difficult to detect planets.
That said, all Sun-like stars end their lives as white dwarfs. Imagine carbon and oxygen cores the size of Earth. Almost all the stars around which we have found planets will therefore end up transforming in this way.
We also know that these objects can host planets, despite a a particularly violent transition process. In fact, toward the end of their lives, stars similar to the Sun begin to swell and become red giants. In addition to swelling in size, these stars also undergo violent spasms that lift large plumes of material into the surrounding system. The planets that are a little too close are then charred before being engulfed.
But even after all this violence, it is still possible for planets far enough away to survive. Interactions between these planets and any newly ejected material from the star can then push them together. New planets can also form from the wreckage of old ones, creating a new planetary system.
JWT to discover them
Discovering these planets is a challenge nonetheless. In fact, these objects are very small and relatively dark transit method commonly used for detecting exoplanets does not work. On the other hand, white dwarfs do not have many notable features in their spectra. Thus, the second popular method is that radial velocity which is to observe the redshift and blueshift of spectral features when an orbiting planet pulls on its parent star does not work either.
However, identifying Earth-like planets around white dwarfs would be very interesting. This can actually help us to understand the ultimate fate of our own solar system. Incidentally, it could also multiply goals in the hunt for extraterrestrial life.
But if current methods don’t work, what to do? A few days ago, a team of astronomers published a roadmap suggesting that we could uncover these potential worlds thanks to the James Webb Telescope (JWT). According to them, looking at them would be sufficient.
If white dwarfs are relatively cool, any orbiting planet would be relatively hotter. This means that the infrared light coming from a white dwarf would also contain some of the infrared light from the orbiting planet. By comparing this light combined with the light of a white dwarf, which we know has no planets, we could thus suggest the presence of an exoplanet.
In their paper, the astronomers note that JWT could observe the fifteen closest white dwarfs and potentially find planets in their habitable zones, provided the planets are the right size and temperature. The light from worlds too small and too cold was actually indistinguishable from that of their white dwarf.