One day our sun will die.
Since we happen to be inhabitants of the solar planetary system, we are very interested in when and how this happens.
Of course, we’re unlikely to see it anywhere near…but, you know, it’s our home. We wondered what it would end up being. Curiosity aside, models of stellar evolution can help us understand the universe and our own place in it.
“If we don’t understand our own sun — and there are so many things we don’t — how can we expect to understand all the other stars that make up our wonderful galaxy,” said astronomer Orlagh Creevey of the Observatory de la Côte d’Azur in France .
We’ve got a detailed look at what’s going to happen to the sun’s future. It will continue to get hotter over the next billions of years, eventually running out of hydrogen to fuse to its core.
The core will begin to shrink, a process that brings more hydrogen into the area around the core, forming a hydrogen shell. This hydrogen then begins to fuse, dumping helium into the core, a process called shell burning.
During this time, the Sun’s outer atmosphere expands a lot, possibly even extending into Mars’ orbit, turning it into a red giant star. Eventually, it will run out of hydrogen and helium, ejecting all the outer material to form a planetary nebula, and the core will collapse into a white dwarf, which may take trillions of years to cool completely.
But when the main sequence stars end depends on the individual characteristics of each star. As far as our own sun is concerned, the rough figure of when things will go south can always use more evidence.
The best way to find this out is to look for sun-like stars in the Milky Way at various stages of life, and then weave them into a timeline that simulates the past and future of our own stars.
With the release of the latest data from the European Space Agency’s Gaia Galaxy Mapping Project, we now have the most detailed timeline of the Sun’s life to date.
Gaia’s primary mission is to map the Milky Way with the highest precision, and it is equipped with a suite of instruments for that mission.It tracks the positions and motions of stars in the sky while observing each star’s brightness and Spectral classification.
These values can be used to determine factors such as chemical composition and temperature. They can also be plotted on a graph called a Hertzsprung-Russell diagram, which gives an estimate of a star’s age.
You see, the mass of a star doesn’t really change with age. But it does have a very significant temperature, which is observed as a change in brightness based on the nuclear fusion that takes place in the core of the star.
Classified as a G-type main sequence star or yellow dwarf (although it’s not actually yellow), our sun is a fairly typical example of its kind.
It is about 4.57 billion years old, or about half the life of its main sequence star. It is also capable of core thermonuclear fusion, producing a surface temperature of 5,772 Kelvin. This means that looking at other G-type stars should give us a good idea of how our sun continues to burn fuel, and when it will eventually die.
Creevey and her team initially began combing through the Gaia data because they wanted to make precise observations of relatively “cold” stars with temperatures between 3,000 and 10,000 Kelvin. That’s because cooler stars tend to be smaller and live longer than their warmer counterparts; therefore, observing cooler stars may reveal more about the history and stellar evolution of the Milky Way and the wider universe.
Because this temperature range includes stars like the Sun, the data can be used to zero in on stars with a similar mass and chemical composition to the Sun. This results in 5,863 Sun-like stars, ranging from very young to very old, across the Hertzsprung-Russell map.
By identifying only the most Sun-like star, Creevey and her colleagues were able to determine when it died.
Roughly consistent with previous predictions of the Sun’s lifespan, its temperature will peak around 8 billion years old. It will become a red giant star at an age of about 10 billion to 11 billion years.
For the record, life on Earth only has about a billion years left, unless we do something catastrophically stupid, or something catastrophic happens to us. This is because the brightness of the sun increases by about 10% every billion years. This means that its temperature is also rising. This change sounds small, but it would render Earth unsuitable for life as we know it.
So it’s enjoyable. But there is still work to be done. The new Gaia catalog of sun-like stars could tell us more about how and why we got started here. For example, we can learn whether Sun-like stars all behave the same. And, more importantly, look for more planetary systems that look like our solar system.
Currently, we have not discovered any systems that appear to be capable of hosting technologically advanced life as we know it. But the answer is there. If we can find them.