The sun is smaller than we thought it was

Measurements of sound waves passing through the sun seem to confirm that it isn’t as big as we thought and we don’t fully understand its interior

The sun is smaller than we thought it was
The Sun is not quite as big as we thought, so may release solar flares differently to how we expect
 (Credit: NASA)

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’s size by measuring the part that emits light, called the photosphere. This is done during a solar eclipse.

A different estimate of the sun’s radius can be found by measuring sound waves travelling through it. In the 1990s, astronomers did this using sound waves near the sun’s surface, called f-waves.

By using a model of the sun’s interior and the circulation of its plasma – a hot gas stripped of electrons – 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’s interior was incomplete.

Now, Douglas Gough at the University of Cambridge and Masao Takata 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. “Seismological inferences are saying things that relate to the nuclear reactions, the chemical composition and the basic structure of the sun,” he says.

Gough and Takata say a different radius would also mean different depths for the layers of the sun’s plasma.

“There’s the potential to reach misleading conclusions about the subtle elements of the sun’s internal structure” if we have the wrong radius, says William Chaplin at the University of Birmingham, UK.

Figuring out how the sun’s 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’s internal structure to fit with the radius is no easy task, says Emily Brunsden at the University of York, UK. “To understand the reason for their difference is tricky, because there’s just a lot of things going on,” she says.


arXiv DOI: 10.48550/arXiv.2310.11299

Post a Comment

Last Article Next Article