7 Betelgeuse
The explosion visible from Earth
Famed for its size, changeable magnitude, pulsating shape and a mispronounced name, the red supergiant Betelgeuse may have already gone supernova. It lies 642 light years away, so we might not know about it for centuries, but to our descendents it will greatly outshine the Moon in the night sky and will remain visible for months before gradually fading away.
Betelgeuse forms the right shoulder of the constellation Orion and is under 10 million years old; it’s a toddler in stellar terms. But the cool, slowly rotating Betelgeuse started life at 15 to 20 solar masses and evolved rapidly.
Hundreds of times younger and larger than the Sun, it has probably already exhausted the hydrogen in its core, and in 2014 it was suggested that it might be consuming its carbon and oxygen reserves. It will then burn higher elements and could explode within 100,000 years, ending its life as a feeble neutron star.
The key to understanding Betelgeuse’s fate is to establish why it loses so much mass. As it fuses higher elements, its bloated atmosphere expands and its surface gravity weakens, shedding a million times more mass per year than the Sun. Rather than a solar wind, Betelgeuse pumps out a hurricane of giant plumes. A multi-layered pulsating ‘shell’ of ejected material lingers around the star and might be responsible for a 15 per cent contraction in its apparent size. Astronomically speaking, Betelgeuse’s doomsday is close. And the effect on our descendents? Comfortingly, it is too far away to cause Earth any harm.