Our sun is fractionally smaller than it seems, which could change our understanding of its internal structure and behaviour.
Historically, astronomers have estimated the sun鈥檚 size by measuring the part that emits light, called the photosphere. This is done during a solar eclipse.
A different estimate of the sun鈥檚 radius can be found by measuring sound waves travelling through it. In the 1990s, astronomers did this using sound waves near the sun鈥檚 surface, called f-waves.
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By using a model of the sun鈥檚 interior and the circulation of its plasma 鈥� a hot gas stripped of electrons 鈥� beneath the surface, these researchers found the photospheric radius to be slightly smaller than the directly measured photosphere, which suggested that our understanding of the sun鈥檚 interior was incomplete.
Now, at the University of Cambridge and at the University of Tokyo have calculated the solar radius using a different kind of sound wave, called p-waves, which are created by the movement of material inside the sun and can pass easily through its core. Their calculation also gives a smaller result than the measured photosphere, by a few hundredths of a per cent.
That difference is big enough to alter what properties we infer the sun has based on the vibrations picked up from its seismology, says Gough. 鈥淪eismological inferences are saying things that relate to the nuclear reactions, the chemical composition and the basic structure of the sun,鈥� he says.
Gough and Takata say a different radius would also mean different depths for the layers of the sun鈥檚 plasma.
鈥淭here鈥檚 the potential to reach misleading conclusions about the subtle elements of the sun鈥檚 internal structure鈥� if we have the wrong radius, says at the聽University of Birmingham, UK.
Figuring out how the sun鈥檚 radius and its internal structure relate could also be useful for understanding other stars, he says.
However, working out how to change our model of the sun鈥檚 internal structure to fit with the radius is no easy task, says at the University of York, UK. 鈥淭o understand the reason for their difference is tricky, because there鈥檚 just a lot of things going on,鈥� she says.
arXiv
