The Earth meets several of the fundamental conditions for life as we know it. Whether in our size, as well as our distance from the Sun. Despite this, a common theme in science fiction is humanity’s colonization of other planets. Despite still being a matter of fiction, this is getting closer to reality, between advances and setbacks. Urgent challenges posed to our species, such as global warming, also make us question whether everything here would be lost. That is, if it wouldn’t be better for us to focus our efforts on getting off Earth.
Science has pointed out that there is hope on our planet if we change things around here. What not everyone imagines, however, is that we will actually have to leave Earth at one time or another. And it is the evolution of the Sun itself that will force us to do this. There is no reason to panic, however. At least not now, but probably in about 1 billion years.
the sun between life and death
The evolution of a low- or medium-mass star, like the Sun, follows a stable life at its inception. After its birth, in an agglomeration of dust and gas called a molecular cloud, it spends most of its life burning hydrogen at its core to generate energy. After extinguishing its initial fuel, the star grows and starts to burn other elements. After a certain moment, however, this is no longer possible, depending on the mass of the star. A collapse occurs, as it can no longer produce energy to compensate for its own gravity. Unlike a supernova process, however, the star in question does not explode. Instead, it releases its external material into a cloud of gas. Its core becomes a white dwarf, a dense, tiny star on its way to death, surrounded by the cloud we call a planetary nebula.
Planetary nebulae are widely studied by astrophysicists. They can provide important information about what life is like for a star and even about the galaxy. They are common objects throughout the universe and true spectacles for our eyes. But the result of this whole beautiful process is not so beautiful for us. The Sun is expected to increase its brightness every billion years by about 10%. It may not sound like much, but that percentage would already represent catastrophic changes on our planet. Furthermore, its transformation into a red giant would devour the Earth and the entire Solar System to Mars.
This entire process is well known to scientists. The observations also support theories of stellar evolution. This is not to say, however, that there are no more questions to be asked. Indeed, new theoretical models have shed light on some hitherto unanswered questions about the Sun’s death.
The enigma of planetary nebulae
A few decades ago, astronomers noticed that the brightest planetary nebulae in other galaxies had similar brightness. Time had shown the data to be correct and quite useful even for calculating object distances, but the models made no sense. That’s because, in theory at least, older, less massive stars should produce weaker-bright nebulae. The reverse would happen for younger and more massive stars. That is, observations showed that even stars like the Sun could have bright nebulae. The models, however, said that this would only happen for at least twice the mass of our star.
A 2018 paper published in the journal Nature Astronomy has something different to say. Scientists, with new theoretical models in hand, were able to predict a new lower limit for the formation of a planetary nebula. A star with a mass close to solar would produce a faintly glowing nebula. Stars above 3 solar masses, in turn, would produce the brightest. Between the two limits, the predictions are in great agreement with the data.
With the new works, we can have more information about the history of low and medium mass stars. But we can also learn more about the future of our own star. And, consequently, that of Earth.