The future of the Sun it is written. Like any star its size, it is expected that there will come a time when it runs out of fuel, swelling and becoming a red giant. Then, later on, it will expel its outermost layers and its core will collapse under the effect of gravity, becoming a cold and dense white dwarf. It will be a process that will take about 5,000 million years to occur and that, logically, will influence the planets that revolve around it. Including Earth. That’s why scientists are so interested in studying exoplanets around white dwarfs. They want to “travel to the future” and see what will become of our own planet and its neighbors.
The problem is that, while many of these exoplanets have been found, it is generally very difficult to delve into their atmosphere and study their history. Until now, it had been impossible, but the James Webb Space Telescope has arrived to change that trend.
Colder than expected. A team of scientists from several American universities has used the James Webb to enter the atmosphere of WD 1856bsimilar to Jupiter in orbit and size, which is currently orbiting a white dwarf. James Webb is not capable of solving the reasons why it is so complicated to study these exoplanets. However, thanks to the development of new analysis models, these researchers have been able to analyze its atmosphere.
The composition, in reality, has not caught their attention too much. On the other hand, its temperature has. If we compare it with Jupiter, a temperature of -113ºC would be expected. However, 126ºC was measured. It is too hot, both for an exoplanet around a white dwarf, and for an exoplanet with the characteristics of Jupiter.
Chronicle of a death foretold. In its early stages of life, a star remains “on” while It fuses hydrogen nuclei and transforms them into helium. While this happens in the core, there are two forces that remain in balance. On the one hand, gravity, which pushes all the material inward. And, on the other hand, the radiation pressure, which is generated by the effect of fusion in the stellar core and pushes outward. So far so good. The problem is that hydrogen is not infinite. When spent in the core, the forces are no longer in balance. Gravity overcomes radiation pressure, so the core is pushed inward and compressed. It heats up so much that the helium that remained in the core acquires the ability to fuse, becoming a new fuel, which will be transformed into carbon and oxygen.
All this heating also “ignites” the hydrogen in the outer layers, which until now remained inactive. It begins to merge as well and the star grows outward. We have a big, hot red giant. The process repeats itself, but there comes a time when these new layers that form are expelled by the stellar winds and only the core remains, now cold and very dense. We have a white dwarf. Logically, it is a process that has consequences on the planets that orbit the star. In the case of the solar system, it is known that Mercury and Venus would perish. With the Earth things are not so clear, but it does not look good.
What exoplanets around a white dwarf tell us. Numerous cases of exoplanets have been detected around white dwarfs. Studying them is opening a window to the future of the Earth and its neighbors. However, it is not something easy to study. Generally, the atmosphere of exoplanets is studied during transits. That is, when the planet passes between its star and our telescopes. At this time, light from the star is filtered through the planet’s atmosphere, so the resulting spectra can be analyzed and its chemical composition understood.
The problem is that, normally, exoplanets are much smaller than their star, but that is not the case with those that orbit a white dwarf. This exoplanet, for example, is seven times larger than its star. Therefore, if normally the atmosphere of a transiting planet is completely on the disk of its star, in this case only a small part is. It was necessary to refine the analysis methods with the James Webb to be able to analyze the atmosphere of WD 1856b.
too hot. The wavelength at which objects emit light can also give us clues about their temperature. Therefore, this procedure was used to calculate the temperature of the exoplanet. As we have already seen, it turned out to be too hot.
The hypothesis. It is not known for sure what causes these inconsistencies, but the study authors have some hypotheses. They consider that the planet possibly reached its maximum temperature billions of years after its star became a white dwarf. Then, far from cooling as it would normally have, it was affected by a nearby binary star, whose tidal influence not only warmed it. It also moved it away from its orbit. All this took him away from what was expected, but above all it kept him alive.
As explained in Science Alert one of the authors of the studyRyan MacDonald, this planet, like all exoplanets around a white dwarf, demonstrates that the death of the star is not the end of the planet, but a new chapter. Earth may not be influenced by a binary star, but there are many factors that can keep it alive. There may no longer be humans to see it, but perhaps there will be a new form of life. If humanity has not destroyed the planet beforeneither may the collapse of the Sun. That’s good news. More or less.
Image | NASA, ESA, CSA, R. Crawford (STScI)
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