Mysterious crosses

By Elf Eldridge 16/05/2012


Continuing from my last post, where I mentioned a few of the crosses in our southern skies, I’m going to take a closer look at some of the weird and wonderful objects located near them, namely the Carina and Keyhole nebulae, the ‘Southern Pleiades’,  one of the few naked eye Wolf-Rayet stars and NGC2516.

Keyhole Nebula

Keyhole Nebula

I’ve mentioned the glorious Carina nebula before (it’s visible as the pink cloud above the diamond cross in the last image of my previous post), sitting halfway between the southern and false cross. However, buried within the bigger and brighter Carina nebula, lies the Keyhole nebula — a cool, dim cloud of dust and gas only visible as it blocks the light from the bright nebula behind.

Southern Pleiades

IC2602

This wondrous open cluster (actually it’s what appears to be the ‘top’ star of the diamond cross to the naked eye). Like many open clusters, these stars are young and hot, but are a lot dimmer than the actual Pleiades that lie within Taurus. Regardless — they’re quite stunning even with a pair of binoculars.

NGC2516*

NGC2516

Below tip of false cross, lies this open cluster that contains 2 bright ‘red giant’ stars (large cool stars nearing the end of their lives) and several ‘binary’ stars (systems of 2 stars that orbit each other). Unfortunately you need a small telescope to resolve the individual stars of the binaries, but the varied colour of these close by stars make this cluster well worth a look!

Gamma Velorum

Artist's impression of a Wolf-Rayet star

Gamma Velorum, a group of bright stars in a direct line between the two middle stars on the false cross, is included here because of the rarity and strage-ness of a star it contains. The brightest star in the cluster is an example of a ‘Wolf-Rayet’ star, a type of massive star that shines with a very strange light. Typically, stars are hottest in their centre where fusion reactions are occurring, but are cloaked in a shell of cooler gas (which, incidentally) is what we actually see when we look at our sun — a shell of material at about 6000 degrees whereas the inside is several million degrees). Wolf-Rayet stars, are stars whose inner fusion reactions are so violent, that they have blown off this outer shell and so we are able to ‘see’ in inner heart of the star itself. This only happens when a star is reaching the end of its life as they hurtle inexorably toward their deaths as spectacularly violent supernovae. The Wolf-Rayet in Gamma Velorum is one of the few visible to the naked eye, and whilst at first glimpse it may not appear too different to other stars, is undoubtedly one of the most mysterious stellar forms we know of!