Friday, 15 April 2016

Betelgeuse's Ring

Betelgeuse, Orion's right shoulder, is a most fascinating star. Not only is it the 8th brightest star in the sky but also its strong, red colour has inspired all cultures around the world since the dawn of civilisation. As I've explained before, a red colour means that a star's actually quite cold. The temperature on its surface is barely 3.000°C, which is 2.500°C cooler than our Sun. But... Betelgeuse's also one of the largest stars that we know. It's so large that if it were at the position of our Sun, its surface would extend beyond Jupiter's orbit. Or to give you a better idea of its size... imagine that the Earth is a grain of sand with a diameter of 1mm. In comparison, our Sun would be the size of a grapefruit. And Betelgeuse would be... Wembley Stadium! That's how big it is! Then again, although Betelgeuse could contain 1,6 billion suns, its mass is estimated to be only 20 solar masses, making it an extremely low-density star. What's more, Betelgeuse is rapidly losing a lot of its mass. Observations with our most powerful telescopes revealed that it's ejecting enormous plumes of gas. Its surface is also terribly unstable and scientists believe that the star's contracted more than 15% over the last 20 years. Also its brightness shows big variations; the biggest of any bright star in our sky. In 1927 it only appeared to be the 20th brightest star but sometimes it outshone Rigel and Procyon to become the 6th brightest. 

The reason for all of these spectacular figures is that Betelgeuse's arrived at the end of its very short life. Also this is hard to believe if you consider that our Sun's 4,6 billion years old and only halfway its lifecycle, but Betelgeuse's only 10 million years old! It was born long after the age of the dinosaurs, in the period that the big apes appeared and the flora and fauna on Earth started to take their present shape. The greater the mass of a star, the faster it consumes its energy source and eventually dies. We believe that Betelgeuse was born in the Orion Nebula complex as a star with a very large mass which burnt up very quickly. When its core ran out of hydrogen, it started to fuse helium into oxygen and carbon, greatly expanding the star's radius and causing the star to cool down. Claudius Ptolemy described Betelgeuse as ruddy in the 1st century AD, but interestingly, Chinese astronomers who observed the star 3 centuries earlier, said it was yellow. So we could conclude that the cooldown from a yellow to red supergiant star occured very recently. 

Another interesting fact is that Betelgeuse's shooting through our universe at a speed of 30km/s, more than 3 times the speed a rocket needs to escape Earth's gravity or 90 times the speed of sound! As such, it's creating a shockwave that distorts space around it. Gas and dust are blown away and ripple in its wake and this is exactly what I wanted to show you on my sketch. I know, it's very difficult to see. Believe me, I had a hard time seeing it through my binoculars but eventually I did notice a kind of weird, dark triangle surrounding the star. This triangle's known as Betelgeuse's Ring and they are clouds of dust blown away by the quickly approaching giant star. So indeed, these clouds are dark because they're closer to us than the star and so they partly block its light. 

But as I said, Betelgeuse's fast life of rock 'n roll will soon come to an end. It's already terribly unstable. Cooldown's reached a critical point. Iron's building up in its core. And then... it will explode in a gigantic supernova explosion, probably within the next 100.000 years already. It will be brighter than a full Moon and last for several months! But don't worry, there's no need for panic. Betelgeuse's between 500 and 600 lightyears away and although some lunatics have predicted doom or even judgement day, the radiation from this explosion will be far less than the radiation we receive from our Sun, so we'll be quite safe.


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