James Webb discovered two exoplanets that survived the death of their stars

Space Observatory named after. James Webb made two rare observations — directly saw two exoplanets in systems with white dwarfs. This is exoticism squared — receiving light from planets outside the solar system that have still survived the death of their star.

Artist's representation of a giant exoplanet in a white dwarf system. Image source: Robert Lea

The article about the discovery has not yet been peer-reviewed and is on the arXiv website. The exoplanet candidates were discovered by MIRI's Webb instrument in the mid-infrared, when the white dwarfs WD 1202-232 and WD 2105-82 came into view of the telescope. One of the potential exoplanets is located at a distance from the star about 11.5 times further than the Earth is from the Sun. The second candidate is even further from its star — at a distance of 34.5 times further than the distance between our planet and the Sun.

The masses of both exoplanets are still unknown. New observations are needed to determine them. According to rough estimates, each of the exoplanets can be from 1 to 7 times heavier than Jupiter, the largest planet in the solar system. Until the mass of these objects is determined, they will be considered exoplanet candidates.. Their previous orbits were apparently much closer to the stars. Probably approximately where the orbits of Saturn and Jupiter are now. When the stars in these systems died and turned into red giants, their overgrown shells burned out and pushed everything into the orbit of Mars, and this could also lead to changes in the orbits of the giant exoplanets.

Looking at the systems WD 1202-232 and WD 2105-82, we are actually observing a cast from the Solar system in about 5 billion years, when the Sun will go through the red giant stage and shed its outer shell, leaving a cooling core — a white dwarf — in the center of the system.

Image source: Mulaney, et al, 2024

By the way, from 25% to 50% of observed white dwarfs show an increased content of metals according to the astronomy classification — chemical substances heavier than hydrogen and helium. Using the example of observed systems with surviving giant planets, it can be assumed that they drop asteroids and comets onto the cores of stars, being sources of contamination of stellar remains with metals. Thus, giant planets can be considered common bodies in stellar systems.

Another interesting observation of exoplanet candidates was that they were much hotter in a certain range of the infrared spectrum than would be expected. This allows us to hope that additional heat may come, for example, from their satellites. This gives us a chance to discover an exomoon for the first time.. In a word, objects that are very promising for observation have been discovered, and Webb will certainly pay attention to them.