Star profile: Betelgeuse
All About Space|Issue 109
Star profile: Betelgeuse
The famous red giant will soon be coming to an explosive end
Betelgeuse, or Alpha Orionis, has had an eventful 8.5 million years, and astronomers predict it has less than a million years left. If you were to go outside and stare out at the night sky, you’d recognise Betelgeuse quite easily within Orion, shining with an apparent magnitude of +0.5. However, this figure has been known to vary due to the star’s instability, which causes pulsations in the star’s outer layers and in turn expells material into its surrounding environment.

The star is relatively nearby at just 642 light-years away, and exists as an enormous red supergiant star. If it were placed in the centre of our Solar System, its outer surface could stretch to around the orbit of Jupiter. This Herculean size is due to an imbalance within the star’s interior. Towards the end of any star’s life, a lifetime of nuclear fusion – the process in which hydrogen fuses into helium within a stellar core and releases energy – has inevitably depleted the hydrogen fuel source that keeps the fire burning. This results in overpowering gravity putting strain on the core, which is experiencing a depleting radiation pressure output. This ignites nuclear fusion in the outer layers of the star, and the core then begins to convert helium into heavier elements such as carbon, oxygen and so on. The resultant radiation pressure within Betelgeuse’s outer layers has pushed the surface of the star outwards, bloating it into its current supergiant status.

Betelgeuse – like any star – began as a cloud of gas and dust, and was able to gravitationally accrete 15 times the mass of our Sun at a time when Earth was already almost 4 billion years old. Based on microfossil evidence, life in its simplest form had already been around for approximately a billion years. This shows how rapid Betelgeuse’s birth and evolution have been. However, this is the usual trend when it comes to stars with significantly more mass than our Sun: the biggest and brightest stars always burn out the fastest.

In the next 100,000 years or so, Betelgeuse will explode in an extraordinary fashion, visible throughout the cosmos. This is known as a supernova, and it starts when the star’s core begins to form iron. As nuclear fusion creates elements heavier than helium, there comes a point when iron is formed. If you want to create a heavier element than iron, the process requires energy from its environment, instead of emitting it. This is referred to as an ‘endothermic reaction’. This will lead the interior of Betelgeuse to collapse in on itself and ricochet off the iron core, resulting in a supernova explosion. This explosion will light up the sky on Earth, even in broad daylight. This is not a cause for concern, however, as astronomers predict that the resulting shock wave would have to travel for about 6 million years before it came close to Earth. At this point it will have slowed down to be nothing more than a light breeze on the Solar System’s protective bubble.

NEWS FROM Betelgeuse

Mysterious dimming

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Issue 109