22-Nov-19 : "Come on, Betelgeuse... Come on..."
Winter heralds the arrival of another strange and beautiful object to the Eastern skies and, every time I see it, I begin to chant a strange and unusual Mantra : "Come on, Betelgeuse. Come on Betelgeuse".
So what's this odd thing called Betelgeuse and why do I find myself repeating a frankly rather childish (and perhaps a little ghoulish) incantation in a graveyard at the front of my house around midnight so close to Hallowe'en?
For those of you not already familiar with this particular celestial phenomena, Betelgeuse is a star. You'll find it in the constellation Orion, which is a particularly easy constellation to locate.
The constellation Orion represents Orion the Hunter in Greek mythology. It's big and covers a substantial area of the winter sky. It's also readily identifiable, framed, as it is, by a rectangle of four really bright stars. To find Orion, just wait until shortly after midnight and look towards the east - Orion should be rising over the eastern horizon.
The name 'Betelgeuse' is Arabic and pronounced Beetle-Juice. This isn't unusual. Lots of stars have Arabic names because, way back in the Golden Age of Islamic Science, Arabic astronomers obtained star catalogues produced by Greek, Babylonian and Indian astronomers, and translated them into Arabic. These volumes then spread through the Islamic Empire where they were picked up by European astronomers, and the names stuck.
Betelgeuse itself sits at Orion's right shoulder - that's Orion's right and our left - and, even with an unaided eye, you should notice that it's an odd colour. To my eyes, it's yellowish red. You may see it differently though.
What's special about Betelgeuse? Betelgeuse is what astronomers call a Red Super Giant, which, in layman's terms, means that it's very big and very red. That might sound astonishingly obvious and it is. "You actually get paid for this sort of guff?" I might hear you ask and, again, you'd be right - I do - but… Betelgeuse is interesting for all sorts of reasons.
Firstly, we're pretty confident that Betelgeuse is rapidly approaching the end of its life. That's not unusual. Stars do that all the time. What makes Betelgeuse special is that it's not very old at all and, in stellar terms, it's just a youngster.
Not very old? How old is Betelgeuse?
Stars like our Sun live for quite a long time. We think that the Sun is around four and a half billion years old, give or take, and our current theories suggest that it will last for another five or six billion years before it too yields to the ravages of old age.
The Sun is an unremarkable star in many ways. It's not particularly massive for a start. Actually, it's a little on the small size. As a consequence of it's diminutive size, the Sun burns its fuel at a relatively slow rate. This means that it's not particularly hot when compared to other stars.
Compare and contrast our Sun with Betelgeuse.
According to current theories, Betelgeuse was originally a huge star - many, many thousands of times more massive than our Sun.
Now, this may seem completely counter-intuitive but big stars burn faster than small stars. Surely, if you make a bigger bonfire then it takes longer to burn. Not so with stars. The more mass there is then the greater the number of nuclear reactions that can take place at a particular moment in time and the faster the star's fuel is converted to energy. Consequently, big stars burn hotter than little stars, which means that they also consume their available fuel at a greater rate.
If this is the case (and it seems highly likely) then Betelgeuse may only be a few tens of millions of years old and, more so, when we look at Betelgeuse with a telescope, when we examine it's chemical and physical make-up, when we compare it with other stars then we're forced to conclude that Betelgeuse maybe very close to the end of its life, and that might just have some interesting consequences for us here on Earth.
Betelgeuse is a remarkable star and astronomers have puzzled over its behaviour for centuries. Back in the 1800's, Sir John Herschel noted that the star was variable, and then it wasn't, and then it was again, which was puzzling. Albert Michelson, an American astronomer, set out to do something remarkable - he attempted to measure the actual size of the star. He succeeded but he didn't get the answer he was expecting. The value he obtained (using a device of his own devising called the Michelson Interferometer) was far larger than expected and implied that Betelgeuse had a diameter which was roughly the size of Jupiter's orbit. In other words, the star's outer atmosphere had expanded massively, consuming all of the star's inner planets.
If that's the case then how do we account for the changes in brightness? Why is Betelgeuse variable?
We think that Betelgeuse has a least one outer shell of hot gas, which is pushed outwards through space by Betelgeuse's equivalent of our solar wind and lots of evidence from our space telescopes seems to support this view.
The star's outer atmosphere is pushed away by some kind of cataclysmic explosion and expands quickly into space. This expansion causes the shell to cool off, and so the outer shell falls back towards the star, where it heats up again. Hence, we see a jump in the star's brightness as it heats up followed by a period of cooling where the star is not as bright as it was. Okay, so this is a rather simplistic explanation but will serve our purposes for the time being.
Here's in the interesting bit… This cyclic behaviour can't go on forever. Eventually Betelgeuse is going to run out of fuel and the solar wind which pushed those outer shells further and further away from the star will eventually fall off to nothing and if there's nothing to push those shells away then gravity will take over and pull them back to the point where they fall into the star and… the star goes BOOM!
Betelgeuse is, or was, a big star and when that amount of matter collapses back in on itself, the result is what astronomers call a Supernova. When this happens, a huge proportion of the star's mass is converted into energy and the star's brightness jumps enormously, to the extent that the star's energy output is more than every other star in the galaxy combined, albeit very, very briefly. How briefly? Probably a few months, maybe a little more or a little less, which doesn't sound particularly brief but, in stellar terms, it's a mere instant in the star's life.
What does this mean for life on Earth?
Well, very little actually. Betelgeuse is a long way off, at around six hundred and forty two light years distant. What that means that it takes the light from Betelgeuse roughly six hundred and forty two years to reach us so if Betelgeuse did go Supernova tomorrow, we wouldn't know for another six hundred and forty two years. That said, if Betelgeuse did go Supernova six hundred and forty two years ago then we might see the consequences tomorrow. Or the next day. Or the day after that.
What would happen here on Earth? Well, we'd suddenly see a very bright star in the sky. We reckon that it would be about as bright as the full moon and therefore visible in daylight. At night, it would shine incredibly brightly. Astronomers would have to wait until Betelgeuse had set before we could do any meaningful observations of the sky.
What about the region of space around Betelgeuse? What would happen there?
That's a really interesting question. We do know that when a star goes nova or Supernova, it sends a shockwave moving through space and that shock wave can bump into pockets of interstellar gas and that collision can trigger new stars to form. Okay, so that would take a long, long time to happen but it's probably that we'd later see a series of other stars all burst into life at roughly the same time, astronomically speaking. When a star dies, it usually causes other stars to be born, and that's happened many, many times in the past, a phenomena which I'll talk about in a forthcoming addition to the blog.
So, to answer the question at the top of this blog, that's why you'll find me in a graveyard at midnight around Hallowe'en, egging Betelgeuse on towards its final messy demise.
"Come on, Betelgeuse. Come on Betelgeuse"
"Come on, Betelgeuse. Come on Betelgeuse".