A star runs out of juice? Explodes?

The bushfire smoke has pretty well cleared,  and sometimes we're even getting clear night skies. It was time to take a look at poor old Betelgeuse.



Betelgeuse, nowadays usually pronounced 'Beetle Juice' for some reason, is in trouble. It's well known to be a variable star, with its magnitude fluctuating typically between 0.0 and 1.3. It's an orange-red colour, and it's usually the second brightest star in Orion, the Hunter.

Top left is my picture from last night. Betelgeuse is not even a first magnitude star.

Here's a picture I took in March 2016. That's the Betelgeuse we knew and loved!

It's known that this sort of behaviour in a variable star can be indicative of an imminent supernova explosion. Watch out for this. It would be the brightest thing in the sky apart from the sun. It's fortunately about 700 light years distant. If it was one of the closer stars it could fry us along with all other life on the planet!

'Imminent' in this context means any time in the next 100,000 years, but you never know. It could be tomorrow! Here's a piece from Forbes magazine about a Betelgeuse explosion: Forbes Betelgeuse explosion article

We are stardust (billion year old carbon)

So said Joni Mitchell in her classic 1970 song 'Woodstock' ( https://www.youtube.com/watch?v=cRjQCvfcXn0 ) and of course she was right. Here's a 2014 interview with a somewhat older Joni Mitchell, in case you're a fan: https://www.youtube.com/watch?v=HajWhhXkfYQ

Joni was taken ill a few weeks ago and the reporting suggested she was about to leave us. Thankfully she came good again.

But this wasn't supposed to be a post about Joni Mitchell. It was supposed to be about a current astronomical phenomenon I've been following: the nova ('new star') in Sagittarius. Here's my picture, as of early morning on 14 April. There's a star there that wasn't visible before, and it's been fluctuating noticeably in brightness for a few weeks now. Sure, it's not all that bright, but there was nothing at all to see there before!

Novas are thought to be massive nuclear ignitions of material pulled out of red giants by their white dwarf companion stars. The star consequently becomes tens of thousands of times brighter for a while. It'll probably fizzle out again soon. It's actually supernovas, which are vastly brighter still, which blow themselves to bits and spread their stardust around. Only extremely massive stars become supernovas, and there's only one in our galaxy every few hundred years. (I remember seeing the 1987 one in a neighbouring galaxy though.) All matter, other than hydrogen, is made in stars, and it's mainly through supernovas that all this stuff gets spread around. So 93% of the matter inside us is stardust from supernovas, as I understand it. More on this at: http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/supernovae.htm