An international team of astronomers, led by Dr Thavisha Dharmawardena from the Max Planck Institute for Astronomy, have demonstrated that the dimming was most probably caused by giant star spots covering up to 70% of Betelgeuse's surface.

Astronomers had suspected that a collection of this dust was absorbing the light from Betelgeuse - but no such dust was showing up even when the light from the star was studied at different wavelengths.

Dr Dharmawardena and her collaborators measured light from Betelgeuse at a terahertz wavelength - at frequencies thousands of times greater than in visible light.

This was not consistent with what should have been found if the light from the star was being absorbed by dust.

Using high-resolution images of the star captured in December 2019 the team found areas of varying brightness - indicating the presence of huge star spots covering up to 70% of its surface.