In about three and a half billion years, our sun will begin to cool at the surface, ballooning into a red giant star that will eventually engulf all of the inner planets, including Earth.
This scenario is not new, but astronomers have now determined the time and course of this catastrophe more precisely than ever before, as reported by the European Space Agency ESA. To do this, the researchers used recently published data from the Gaia satellite, which has been observing billions of stars with several telescopes since 2014.
“Only when we understand our Sun – and there is still a lot we don’t know about it – can we expect to understand all the other stars in our Milky Way,” explains Orlagh Creevey from the Observatory Côte d’Azur in France the extensive data analysis that she and her colleagues have carried out.
In order to gain new insights into our sun, researchers are studying similar stars. Because we only see our sun at the present time of its development, 4.57 billion years after its formation. Astronomers can only predict the development of the sun by observing many sun-like stars of different ages.
The Gaia data offer this possibility, because in addition to the movement, they also record the size, temperature, mass and chemical composition of the stars. And a close analysis of this data enables astronomers to estimate the type of star and its age, as well as its resemblance to the Sun.
In a first step, Creevey and her colleagues filtered out the stars with the most accurate values from the gigantic amount of data. “We wanted to have the cleanest possible data set with high-precision measurements at our disposal,” says the researcher.
In a second step, the team filtered out all those stars from this selection that resemble our sun in terms of their mass and chemical composition. The bottom line is that although all of these stars are similar to the sun, they are very different in age. Because as long as the stars fuse hydrogen into helium inside and thus generate their radiation, their mass and composition change only slightly. The situation is different, however, with the size and temperature of the stars: both are slowly increasing.
Since the selected Sun-like stars are of different ages, Creevey and her colleagues were able to determine their evolution over time and transfer the results to those of the Sun.
When the Sun is 8 billion years old, its surface will reach a maximum temperature – but only about 20 degrees higher than today’s 6045 degrees Celsius. Then it begins to cool and expand into a red giant.
Only when no more nuclear fusion takes place inside the sun at an age of ten to eleven billion years will the red giant collapse into a white dwarf star just about the size of the earth, which will slowly cool down over billions of years.
Creevey and her colleagues went one step further: From their data, they picked out all those stars that are also similar to the sun in terms of temperature and size and are therefore roughly the same age. They found a total of 5883 “solar analogues” in this way. This list is of great value to astronomers around the world.
Because precise observations of these stars can answer the question of how “normal” our sun is. Or whether the emergence of life on Earth depended on the fact that the sun has special properties that distinguish it from other stars.