“Just So Science” – The Star that Couldn’t Make up its Mind

By Elf Eldridge 31/05/2011

Eta Carina Nebula
Eta Carina Nebula

Whilst at the top of Mount Holesworth during the weekend I was fortunate enough to take a stroll and get a great look at the spectacular Wairarapa stars from 1000m above sea level. I’ve become so used to viewing from sea level (and through the Wellington light pollution no less!) that I had completely forgotten just how easy it can be to find ‘nebulosity’ on a really clear night.

What really took my breath away though was the Large and Small Magellanic clouds as well as the nebula above, within the constellation of Carina. If you want to find the Carina Nebula, it’s almost exactly halfway between the Southern Cross and the False Cross, but what it contains is what’s really fantastic – it’s home to Eta Carina and the Homunculus and Keyhole Nebulae.

Eta Carina
Eta Carina surrounded by the Homunculous Nebula
Keyhole Nebula
Keyhole Nebula (zoomed in)

Eta Carina is a truly bizarre star – although the technical term is ‘peculiar’, meaning that its brightness has changed dramatically over the past 200 years. It has an interesting history too – with Aboriginal and European observers recording it as being the second brightest star in the night sky during the 1840s even though it’s only dim now. Now we think that it underwent a ‘false’ supernova, shedding it’s outer layers in a violent outburst (that we see as the red ‘ring’ of dust around it which is actually a shock wave hitting cosmic gas, remnants of yet another explosion about 1000 years ago), but not quite reaching the point of gravitational collapse required to descend right down to a neutron star, hence it survives to this day. The Keyhole nebulae is a ‘Dark Nebula’ that blocks gas as is names after its distinctive shape. In the night sky they look more like the image below than either of the two above due to false colouring from Space Telescope images.

Eta Carina within the Carina Nebula with the Keyhole Nebula to its right
Eta Carina (brightest object in image) within the Carina Nebula with the Keyhole Nebula (dark patch) to its right

“Such wondrous, fine fantastic tales,

Of dragons, gypsies, queens and whales…

…And once they start – oh boy, oh boy!

You watch the slowly growing joy

That fills their hearts. They’ll grow so keen,

They’ll wonder what they’d ever seen

In that ridiculous machine…”

– Roald Dahl Charlie and the Chocolate Factory