Is there a hole in the sun?
How a strange finding has left us questioning our star
It may be the brightest object in our sky, but the Sun is a dark horse. The more we study it, the more quirks it reveals and recently we have found quite a fundamental one. A new way of modelling the Sun's atmosphere has further widened a gap in our knowledge of its core. This could have implications for the whole of astrophysics, not just the Sun, and it may mean having to rethink a whole century of solar physics. The age, mass and luminosity of billions of stars would have to be recalculated.
Scientists from the Max Planck Institute of Astrophysics (Aldo Serenelli and Martin Asplund), Yale University (Sarbani Basu) and Wichita State University (Jason Ferguson) formulated a new
model of the Sun's surface, its photosphere, that was dynamic and three dimensional. Previous models had been static and one dimensional. In stars, elements heavier than helium are called 'metals' by astrophysicists whether they're metallic or not. The 1D models had a higher proportion of these than the 3D one found was required. Some have put forward the idea that this means that a certain amount of mass has 'gone missing' from the Sun; up to 1,500 Earths' worth.
However, one of the scientists involved in the work, Dr Tiago Pereira of Oslo University has poured cold water on this notion. “I find the idea of missing mass in the Sun to be ridiculous. Some people have made models of the solar interior. Those models are incomplete and lead to more mass than observed. This doesn't mean anything is missing, only our knowledge is incomplete.“
Until the early 20th century no one really knew what powered the Sun's interior. British scientist Lord Kelvin and the German scientist Hermann von Helmholtz both proposed that a ball of gas of the Sun’s size could efficiently generate heat by contracting under its own gravity. The figure calculated by Kelvin in 1862 came to 100 million years; far shorter than the 300 million year-estimate of Earth's age by geologists of the time. But Kelvin also knew the limits of knowledge of the Sun's processes at that time, saying in March's Popular Lectures and Addresses, volume 1, 2nd edition: “Mutual gravitation between the different parts of the Sun’s contracting mass must do an amount of work, which cannot be calculated with certainty, only because the law of the Sun’s interior density is not known.“So this couldn't be the way the Sun powered itself.
It wasn't until Einstein published his work on special relativity in 1905 that the true mechanism was discovered. Deriving the equation E=mc2 from his work, Einstein showed that mass and energy were two sides of the same coin, and that a small amount of mass could be converted into enormous amounts of energy. This was the foundation on which scientists from the 1920s to the 1950s formulated stellar nuclear fusion equations. They showed the Sun is powered by hydrogen nuclei
(74.9 per cent of its mass) fusing into a heavier element, helium (23.8 per cent of its mass), and releasing energy in the process. The other 1.3 per cent is heavier elements – the 'metals' – such as oxygen, carbon and magnesium. 4.25 million tonnes of mass are converted directly into energy every second in the core, making the Sun shine. That may sound like a lot, but it only amounts to 0.15 per cent of Earth's mass since dinosaurs died out around 66 million years ago.
But that isn't the end of the story. The 3D model was tested against the latest spectroscopic observations from the Swedish Solar Telescope in La Palma. The results were good, and also in agreement with other spectroscopic data suggesting the scientists were on the right track. But when
“The problem is most likely with our incomplete knowledge of processes in the core of the Sun”
Charged particles from the Sun trapped in the magnetosphere result in aurorae