What is causing the supergiant star Betelgeuse to dim and change its shape?

News: Using the European Space Organisation’s (ESO) Very Large Telescope (VLT), astronomers have noticed the unprecedented dimming of Betelgeuse.

Facts:

• Betelgeuse is a red supergiant star (over 20 times bigger than the Sun) in the constellation Orion.
• Instead of appearing round, the star Betelgeuse, at present, appears to be “squashed into an ova”.

Additional Information:

Red supergiant Stars:

• These are stars with a supergiant luminosity class (Yerkes class I) of spectral type K or M. 
• They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous