Artist’s impression of some possible evolutionary paths for stars of different initial masses. Some protostars, brown dwarfs, never get hot enough to ignite into full-fledged stars, and simply cool and fade away. Red dwarfs, the most common type of star, continue to burn until they have transformed all their hydrogen into helium, becoming a white dwarf. Sun-like stars swell into red giants before shedding their outer shells into a colorful nebula as their cores collapse into a white dwarf. The most massive stars collapse abruptly after burning through their fuel, causing a supernova or gamma-ray burst and leaving behind a neutron star or black hole. Credit: ESA
We all sometimes wish we could see the future. Now, thanks to the latest data from ESA’s Gaia star mapping mission, astronomers can do just that for the sun. By precisely identifying stars of similar mass and composition, they can see how our sun will evolve in the future. And this work extends far beyond a little astrophysical clairvoyance.
Gaia’s third big data release (DR3) was made public on June 13, 2022. One of the major products that came out of this release was a database of the intrinsic properties of hundreds of millions of stars . These parameters include how hot they are, how big they are, and what masses they contain.
Gaia takes exceptionally accurate readings of a star’s apparent brightness, as seen from Earth, and its color. Converting these basic observational features into intrinsic properties of a star is painstaking work.
Orlagh Creevey, Observatoire de la Côte d’Azur, France, and collaborators at Gaia Coordination Unit 8, are responsible for extracting these astrophysical parameters from the Gaia observations. In doing so, the team is building on the pioneering work of astronomers working at Harvard College Observatory in Massachusetts in the late 19th and early 20th centuries.
At that time, astronomers’ efforts were focused on classifying the appearance of “spectral lines”. They are dark lines that appear in the rainbow of colors produced when light from a star is split by a prism. Annie Jump Cannon devised a spectral classification sequence that ordered stars according to the strength of these spectral lines. This order was later found to be directly related to the temperature of the stars. Antonia Maury made a separate classification based on the width of certain spectral lines. This was later found to be related to the luminosity and age of a star.
The correlation of these two properties allows each star in the Universe to be represented in a single diagram. Known as the Hertzsprung-Russell (HR) diagram, it has become one of the cornerstones of astrophysics. Devised independently in 1911 by Ejnar Hertzsprung and in 1913 by Henry Norris Russell, an HR diagram plots the intrinsic luminosity of a star as a function of its effective surface temperature. In doing so, it reveals how stars evolve over their long life cycles.
The life of a star. Credit: European Space Agency
Although the star’s mass changes relatively little during its lifetime, the star’s temperature and size vary greatly as it ages. These changes are driven by the type of nuclear fusion reactions taking place inside the star at the time.
With an age of about 4.57 billion years, our sun is currently in its comfortable middle age, fusing hydrogen into helium and is generally quite stable; stayed even. It won’t always be like that. As the hydrogen fuel in their core runs out and changes in the fusion process begin, we expect them to swell into a red giant star, reducing its surface temperature in the process. How exactly this happens depends on the mass a star contains and its chemical composition. This is where DR3 comes in.
Orlagh and his colleagues combed through the data looking for the most precise stellar observations the spacecraft could provide. “We wanted to have a really pure sample of stars with high-precision measurements,” says Orlagh.
They concentrated their efforts on stars that have surface temperatures between 3000K and 10000K because they are the longest-lived stars in the Galaxy and can therefore reveal the history of the Milky Way. They are also promising candidates for finding exoplanets because they are very similar to the sun, which has a surface temperature of 6000K.
Orlagh and his colleagues then filtered the sample to show only those stars that had the same mass and chemical composition as the sun. Because they allowed the ages to vary, the stars they selected ended up drawing a line through the FC diagram that represents our sun’s evolution from its past to its future. It revealed how our star will vary in temperature and luminosity as it ages.
From this work, it is clear that our sun will reach a maximum temperature at about 8 billion years of age, then cool and increase in size, becoming a red giant star between 10 and 11 thousand millions of years The sun will reach the end of its life after this phase, when it eventually becomes a dim white dwarf.
The evolution of a sun-like star, derived from data released by the ESA 3 Gaia mission, in the so-called Hertzsprung-Russell diagram. The sun is illustrated at its current age of about 4.6 billion years, and the evolutionary path it will follow as a star’s temperature and luminosity vary with age as it burns its fuel . Our sun will reach a maximum temperature at about eight billion years, then cool and move along this diagram while slowly increasing in size. It becomes a red giant around 10-11 billion years, and then rapidly increases in size significantly. The end of the sun’s life happens soon after, where it will end up as a dim white dwarf. Credit: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO
Finding sun-like stars is essential to understanding how we fit into the wider Universe. “If we don’t understand our own sun, and there’s a lot we don’t know about it, how can we hope to understand all the other stars that make up our wonderful galaxy,” says Orlagh.
It is a source of irony that the sun is our closest and most studied star, but its proximity forces us to study it with completely different telescopes and instruments than we use to look at the rest of the stars. This is because the sun is much brighter than other stars. If we identify stars similar to the sun, but this time with similar ages, we can bridge this observational gap.
To identify these “solar analogues” in the Gaia data, Orlagh and colleagues looked for stars with temperatures, surface gravities, compositions, masses and radii similar to the present-day Sun. They found 5863 stars that match their criteria.
Now that Gaia has drawn up the list of targets, others can begin to seriously investigate them. Some of the questions they want answered include: Do all solar analogs have planetary systems similar to our own? Do all solar analogs rotate at a similar speed to the sun?
With Data Release 3, Gaia’s extremely precise instrumentation has made it possible to determine the stellar parameters of more stars with greater precision than ever before. And this precision will affect many other studies, for example, knowing the stars more precisely can help the study of galaxies, whose light is the fusion of billions of individual stars.
“The Gaia mission has touched everything in astrophysics,” says Orlagh.
Video: Gaia, the surveyor of a billion stars More information: Gaia data release 3: www.cosmos.esa.int/web/gaia/data-release-3 Provided by the European Space Agency
Citation: Gaia mission reveals sun’s past and future (2022, August 11) Retrieved August 12, 2022, from
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